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• #### Question 1 - A new treatment reduces blood pressure for hypertensive patients by 10 mmHg more...

Incorrect

• A new treatment reduces blood pressure for hypertensive patients by 10 mmHg more than the current standard treatment (95% confidence interval minus 2 to 22).Which of the following statements is most accurate?

Your Answer: If the results are from a randomised controlled trial they can be believed to be accurate

Correct Answer: The difference is not statistically significant

Explanation:

If the 95% confidence interval contains zero (more precisely, the parameter value specified in the null hypothesis), then the effect will not be significant at the 0.05 level.If the 95% CI for the DIFFERENCE between the 2 groups contains the value 0, this means that the p-value will be greater than 0.05. Conversely, if the 95% CI does not contain the value 0, then the p-value will be strictly less than 0.05. The same applies when comparing groups using a ratio, such as an odds ratio or risk ratio. When using a RATIO instead of a DIFFERENCE, the situation of no difference between the 2 groups will be indicated by a value of 1 instead of 0. If the ratio equals to 1, the 2 groups are equal. Hence, if the 95% CI of the ratio contains the value 1, the p-value will be greater than 0.05. Alternatively, if the 95% CI does not contain the value 1, the p-value is strictly less than 0.05.

• This question is part of the following fields:

• Epidemiology And Statistics
80.9
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• #### Question 2 - Which of the following is true of randomisation in a clinical trial? ...

Correct

• Which of the following is true of randomisation in a clinical trial?

Explanation:

The main aim of randomisation in a clinical trial is to remove the bias and avoid any potential confounding variables. While in double blind studies both the investigators and the patients are not aware of which group they belong in, being blind is not essential in carrying out a randomized study, nor is it essential that the randomisation be done away from the study centre. A placebo also does not facilitate randomisation, which can be done in single centre and multi-centre trials.

• This question is part of the following fields:

• Epidemiology And Statistics
23.2
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• #### Question 3 - According to a cross-sectional survey of >500 subjects, an estimated 10% of a...

Incorrect

• According to a cross-sectional survey of >500 subjects, an estimated 10% of a group of children that have a sibling with severe eczema, have asthma. On the other hand, only 0.5% without a sibling with severe eczema have asthma. You want to test the difference of 9.5% for significance. Which of the following tests would you use?

Explanation:

To quantify differences between percentages you can use Fisher’s exact test.Odds ratios, relative risks and number needed to treat are ways of quantifying differences between percentages in two groups, however are not in themselves significance tests.

• This question is part of the following fields:

• Epidemiology And Statistics
14.6
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• #### Question 4 - Which of the following statements is true regarding box plots? ...

Correct

• Which of the following statements is true regarding box plots?

Your Answer: Show distributionally outlying values and provide data summaries that are not unduly influenced by those outliers

Explanation:

Box plots can be used to display numerical outcomes and give valid summaries (median and interquartile range or IQR) for any distributional form that the outcomes might take. Additionally, they show outlying values and provide data summaries that are not unduly influenced by those outliersOther options:- The box itself represents the interquartile range, with the two whiskers representing the variability outside the upper and lower quartiles.- Variability is represented with whiskers and feathers are used in fan charts.They are not as informative as showing the actual values but can be used to make comparisons of medians and IQRs between subgroups.

• This question is part of the following fields:

• Epidemiology And Statistics
20.3
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• #### Question 5 - Regarding crossover trials, which of the following statements is true? ...

Correct

• Regarding crossover trials, which of the following statements is true?

Your Answer: Are best for assessing the efficacy of different treatments in giving short-term relief of chronic conditions

Explanation:

Crossover trials are characterized by the switching of study participants throughout the treatment groups, keeping a random order of switching. This randomization is important to determine any carry-over effect of different treatment modalities. The benefit of this study is the evaluation of the efficacy of various short-term treatment options for the relief of chronic conditions. The washout period is small in this type of study. Crossover studies are more efficient than the parallel studies, but they should be used according to the treatment options and outcomes.

• This question is part of the following fields:

• Epidemiology And Statistics
20
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• #### Question 6 - A screening test correctly identifies 90 of 100 individuals with disease and falsely...

Correct

• A screening test correctly identifies 90 of 100 individuals with disease and falsely identifies a further 15 of 300 individuals without disease. Which one of the following statements is true?

Explanation:

The sensitivity of a screening test can be described in a variety of ways, typically such as sensitivity being the ability of a screening test to detect a true positive, being based on the true positive rate, reflecting a test’s ability to correctly identify all people who have a condition, or, if 100%, identifying all people with a condition of interest by those people testing positive on the test.The specificity of a test is defined in a variety of ways, typically such as specificity is the ability of a screening test to detect a true negative, being based on the true negative rate, correctly identifying people who do not have a condition, or, if 100%, identifying all patients who do not have the condition of interest by those people testing negative on the test.Sensitivity=[a/(a+c)]×100Specificity=[d/(b+d)]×100a: True positiveb: False Positivec: False negatived: True negative

• This question is part of the following fields:

• Epidemiology And Statistics
16.1
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• #### Question 7 - Consider the following study:Healthy individuals are assessed according to their current body mass...

Correct

• Consider the following study:Healthy individuals are assessed according to their current body mass index (BMI). Two years later, their health status is reassessed, and the relationships with their earlier BMI were determined.What is the type of epidemiological study described above?

Explanation:

The study described in the question is a ‘cohort’ study.Other options:A prospective observational study – When groups are classified according to one or more factors at a given time and followed forward to determine outcomes (usually some health status)- Although there is in one sense a control group (those who do not develop the health problem), this is not generally called a ‘controlled’ trial. – An ecological study would look at outcomes in different groups (countries or regions usually) who follow different practices.

• This question is part of the following fields:

• Epidemiology And Statistics
14.3
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• #### Question 8 - A two-sample t-test comparing weight loss after two different diet regimes yield a...

Correct

• A two-sample t-test comparing weight loss after two different diet regimes yield a P-value of 0.001.Which one of the following statements can be deducted from this finding?

Your Answer: The difference would have occurred by chance for a study of this size only once in 1000 times if the two regimes did not differ in their effect

Explanation:

The P value is defined as the probability under the assumption of no effect or no difference (null hypothesis), of obtaining a result equal to or more extreme than what was actually observed. The P stands for probability and measures how likely it is that any observed difference between groups is due to chance. Being a probability, P can take any value between 0 and 1. Values close to 0 indicate that the observed difference is unlikely to be due to chance, whereas a P value close to 1 suggests no difference between the groups other than due to chance. Thus, it is common in medical journals to see adjectives such as “highly significant” or “very significant” after quoting the P value depending on how close to zero the value is.A lower p-value is sometimes interpreted as meaning there is a stronger relationship between two variables. However, statistical significance means that it is unlikely that the null hypothesis is true (less than 5%).To understand the strength of the difference between two groups (control vs. experimental) a researcher needs to calculate the effect size.

• This question is part of the following fields:

• Epidemiology And Statistics
191.2
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• #### Question 9 - In a trial for a new treatment of lung disease, a traditional regime...

Correct

• In a trial for a new treatment of lung disease, a traditional regime was given to 130 patients, 30 of whom died, while the new treatment was given to 125 patients, 20 of whom died.   Which of the following tools will be useful in calculating whether the above results are due to chance?

Explanation:

The Chi squared test is used to find the relationship between two variables, determining whether they are not independent of each other. This test of statistical significance allows you to determine the degree of confidence with which you can accept or reject the null hypothesis. The student t test compares the significant differences in data means, while rank correlation, linear regression and the correlation coefficient all help to measure the linear relationship between variables.

• This question is part of the following fields:

• Epidemiology And Statistics
106
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• #### Question 10 - The following is true of power calculations for comparison of a numerical measurement...

Correct

• The following is true of power calculations for comparison of a numerical measurement between the two groups:

Explanation:

Power calculations are a important step in study design and preparation, but do not directly help with the interpretation of the results. They are used to determine how many subjects are needed in order to avoid errors in accepting or rejecting the null hypothesis. These calculations are not usually complex and for the best results, the power of the test should be set to above 80%.

• This question is part of the following fields:

• Epidemiology And Statistics
80.4
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• #### Question 11 - The correlation coefficient is used to determine whether there is a mathematical linear...

Incorrect

• The correlation coefficient is used to determine whether there is a mathematical linear relationship between diastolic blood pressure and serum cholesterol levels in a group of patients with hypertension (both variables have a normal distribution).Which of the following five coefficients is described?

Correct Answer: Parametric Pearson’s correlation coefficient

Explanation:

Correlation is a bivariate analysis that measures the strength of association between two variables and the direction of the relationship.Pearson r correlation: Pearson r correlation is the most widely used correlation statistic to measure the degree of the relationship between linearly related variables. Pearson’s correlation coefficient is the test that measures the statistical relationship, or association, between two continuous variables. It is known as the best method of measuring the association between variables of interest because it is based on the method of covariance. It gives information about the magnitude of the association, or correlation, as well as the direction of the relationship.The non-parametric Spearman or Kendall rank correlation coefficient is used if neither variable has a normal distribution or the sample size is small (i.e. <20).

• This question is part of the following fields:

• Epidemiology And Statistics
18.5
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• #### Question 12 - Choose the standard method for comparing distributions in data sets (such as between...

Correct

• Choose the standard method for comparing distributions in data sets (such as between the expected frequency of an event and the observed frequency of an event) from the list of options.

Explanation:

The Chi-squared test evaluates if two variables are related. The other statistical tests mentioned do not perform this function.

• This question is part of the following fields:

• Epidemiology And Statistics
76.6
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• #### Question 13 - A paired t-test of blood measurements pre- and post-treatment yields a P-value of...

Incorrect

• A paired t-test of blood measurements pre- and post-treatment yields a P-value of 0.256.Which of the following statements is true?

Correct Answer: The paired differences are not significantly different from zero on average

Explanation:

The paired sample t-test, sometimes called the dependent sample t-test, is a statistical procedure used to determine whether the mean difference between two sets of observations is zero. In a paired sample t-test, each subject or entity is measured twice, resulting in pairs of observations. Common applications of the paired sample t-test include case-control studies or repeated-measures designs.Statistical significance is determined by looking at the p-value. The p-value gives the probability of observing the test results under the null hypothesis. The lower the p-value, the lower the probability of obtaining a result like the one that was observed if the null hypothesis was true. Thus, a low p-value indicates decreased support for the null hypothesis. However, the possibility that the null hypothesis is true and that we simply obtained a very rare result can never be ruled out completely. The cut-off value for determining statistical significance is ultimately decided on by the researcher, but usually a value of .05 or less is chosen. This corresponds to a 5% (or less) chance of obtaining a result like the one that was observed if the null hypothesis was true.

• This question is part of the following fields:

• Epidemiology And Statistics
27
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• #### Question 14 - Out of 30 children who are exposed to a chemical, 15 develop a...

Correct

• Out of 30 children who are exposed to a chemical, 15 develop a disorder, compared to only 1 child out of 10 developing the same disorder who were not exposed.The following can be deduced from this information:

Your Answer: The relative risk of exposure to the chemical is 5

Explanation:

Relative risk is the probability of an outcome occurring in an exposed group as compared to the probability of that outcome in an unexposed group. In the scenario given, 50% of the children exposed developed the disease while only 10% of the children who were unexposed developed the disease. The relative risk was therefore 50/10=5. There is no further information about whether the study was controlled, the confidence interval, or the type of study. It therefore cannot be confirmed whether the chemical is causative and if it should be avoided.

• This question is part of the following fields:

• Epidemiology And Statistics
29.2
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• #### Question 15 - A case-control study is developed to assess passive smoking as a risk factor...

Incorrect

• A case-control study is developed to assess passive smoking as a risk factor for the development of asthma in children. The total number of patients recruited for this study is 200. 40 out of the 200 patients report at least one parent smoking in the house when they were younger. 200 more people without asthma are recruited and 20 out of them report that at least one parent smoked in the house when they were younger. What is the odds ratio of patients with asthma having been exposed to passive smoking during their childhood?

Explanation:

An odds ratio (OR) is a measure of association between an exposure and an outcome. The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. Odds ratios are most commonly used in case-control studies, however they can also be used in cross-sectional and cohort study designs as well (with some modifications and/or assumptions). Wherea = Number of exposed casesb = Number of exposed non-casesc = Number of unexposed casesd = Number of unexposed non-casesOR=(a/c) / (b/d) = ad/bc

• This question is part of the following fields:

• Epidemiology And Statistics
178.3
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• #### Question 16 - One of the main disadvantages of case control studies is: ...

Correct

• One of the main disadvantages of case control studies is:

Explanation:

Case control studies are observational studies which retrospectively determine whether a patient might have been exposed to a risk factor for a certain disease, as compared to a control group from the general population. They can be used for a range of outcomes as well as rare diseases. One of the biggest problems with this type of study is recall bias. Research subjects may selectively remember factors that are more predictive of the disease outcome when compared to the control group. All studies should have prior power calculations before the study commences.

• This question is part of the following fields:

• Epidemiology And Statistics
12.4
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• #### Question 17 - In a study, 50 out of 100 smokers developed lung cancers and 50...

Correct

• In a study, 50 out of 100 smokers developed lung cancers and 50 out of 200 non-smokers developed lung cancers. Which of the following is accurate?

Explanation:

Relative risk = (Incidence in exposed group)/incidence in unexposed group). So in this case RR = (50/100)/(50/200) = 2.

• This question is part of the following fields:

• Epidemiology And Statistics
40.2
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• #### Question 18 - A case-control study is being designed to look at the relationship between eczema...

Correct

• A case-control study is being designed to look at the relationship between eczema and a new vaccine for yellow fever. What is the usual outcome measure in a case-control study?

Explanation:

A case–control study (also known as case–referent study) is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case–control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have that condition/disease (the cases) with patients who do not have the condition/disease but are otherwise similar (the controls).
An odds ratio (OR) is a statistic that quantifies the strength of the association between two events, A and B. The odds ratio is defined as the ratio of the odds of A in the presence of B and the odds of A in the absence of B or vice versa.

• This question is part of the following fields:

• Epidemiology And Statistics
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• #### Question 19 - A study done on a group of epileptics records the numbers of...

Incorrect

• A study done on a group of epileptics records the numbers of seizures in the weeks before and after a dietary intervention. The decrease in seizures is on average 20. (95% CI=15 to 25| P=0.0024)Which of the following options is true?

Your Answer: The difference is statistically significant and so the treatment works

Correct Answer: This is a before and after study with no control group and so the results should be viewed with great caution

Explanation:

While the results of this before and after study can provide some preliminary insight into the effects of the dietary intervention, the results should be viewed with great caution as they may be considered merely anecdotal. The lack of a control group contributes to confounding the data. Therefore, while the difference may be statistically significant and the confidence interval is compatible with a fall in the number of seizures after therapy, the results cannot be introduced as the standard without a control group to compare with.

• This question is part of the following fields:

• Epidemiology And Statistics
13.9
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• #### Question 20 - The following best describes non parametric tests: ...

Incorrect

• The following best describes non parametric tests:

Correct Answer: Are less powerful than parametric tests

Explanation:

Compared to parametric tests, non parametric tests are seen to be less powerful as they often contend with fewer assumptions, and may use less information from the data. Sample sizes can be smaller. The samples do not have to follow a normal distribution as in parametric tests, and data may be ordinal, ranked or contain outliers that cannot be removed. Therefore nonparametric tests are well suited for these instances and do not need to be used as a last resort. They are not any more complex than parametric tests.

• This question is part of the following fields:

• Epidemiology And Statistics
13.1
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• #### Question 21 - The positive likelihood ratio for a diagnostic test is 3. A patient, whose...

Incorrect

• The positive likelihood ratio for a diagnostic test is 3. A patient, whose pre-test odds were 2 tests positiveThe following is most accurate:

Your Answer: The likelihood that they have the disease is decreased after the test

Correct Answer: Their prior odds of having the disease are now 6

Explanation:

Before the test, the patient was likely to have the disease being tested for. Their pre test odds were 2, making them twice as likely to have the disease. After testing positive, their pretest odds of 2 and the likelihood ratio of 3 are multiplied to produce 6 as the post test odds. The patient is now 6 times as likely to have the disease after the test. Likelihood ratios above 10 or below 0.1 are strong evidence to rule in and rule out a diagnosis. The negative likelihood ratio is not known here, but does not subtract from the interpretation of the outcomes in this patient.

• This question is part of the following fields:

• Epidemiology And Statistics
62.9
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• #### Question 22 - We want to compare body mass index (BMI) values between children from several...

Incorrect

• We want to compare body mass index (BMI) values between children from several ethnic groups, taking into account differences in the age distributions of the groups.The appropriate analysis is:

Correct Answer: Linear regression analysis with age and ethnicity as predictors

Explanation:

Linear regression is a basic and commonly used type of predictive analysis. The overall idea of regression is to examine two things: (1) do a set of predictor variables do a good job in predicting an outcome (dependent) variable? (2) Which variables, in particular, are significant predictors of the outcome variable, and in what way do they–indicated by the magnitude and sign of the beta estimates–impact the outcome variable.These regression estimates are used to explain the relationship between one dependent variable and one or more independent variables. Three major uses for regression analysis are (1) determining the strength of predictors, (2) forecasting an effect, and (3) trend forecasting

• This question is part of the following fields:

• Epidemiology And Statistics
11.2
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• #### Question 23 - This equation links lung function measurement to height: Lung function = 2.3 +...

Correct

• This equation links lung function measurement to height: Lung function = 2.3 + (1.5 × height), R = 0.75Which of the following statements is true?

Explanation:

The equation, lung function = 3.2 + (1.7 x height) is linear, but this does not necessarily mean that the relationship itself is linear. The equation is able to predict that taller individuals are more likely to have greater lung functions. No information is given on whether the coefficients and the R value are statistically significant.

• This question is part of the following fields:

• Epidemiology And Statistics
18.7
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• #### Question 24 - In a new drug trial, 1 out of 27 individuals who were given...

Incorrect

• In a new drug trial, 1 out of 27 individuals who were given the treatment experienced a side effect, compared to 0 out of the 25 patients given the placebo. Which of the following is true?

Correct Answer: Fisher’s exact test should be used to compare the significance of the difference

Explanation:

The Chi-squared test would have been a useful test to compare the proportions in the scenario. However, due to the small sample size, Fisher’s exact test can be applied to analyse the significance of the difference. Adequate information is not given to determine what sample sizes were used to test the efficacy of the treatment, and to tell whether the treatment should be discontinued without further analysis on the data.

• This question is part of the following fields:

• Epidemiology And Statistics
150.5
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• #### Question 25 - A cohort study is being designed to look at the relationship between smoking...

Correct

• A cohort study is being designed to look at the relationship between smoking and prostate cancer. What is the usual outcome measure in a cohort study?

Explanation:

A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing a cross-section at intervals through time.
The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Relative risk is used in the statistical analysis of the data of experimental, cohort and cross-sectional studies, to estimate the strength of the association between treatments or risk factors, and outcomes.

• This question is part of the following fields:

• Epidemiology And Statistics
11.5
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• #### Question 26 - Which of the following is true in logistic regression analysis? ...

Incorrect

• Which of the following is true in logistic regression analysis?

Your Answer: Should be used to compare proportions of people who test positive between two populations

Explanation:

Logistic regression analysis is an easy to use regression that can serve to estimate how a binary or dichotomous dependent variable, for example whether or not a student passes or fails a medical exam, is related to the number of hours the student studies for the exam. This regression is able to yield an odds ratio, i.e. the probability of passing the exam based on each additional hour of study. As stated, the outcome does not need to be normally distributed but is usually binary. This type of analysis is not complex and does not need to be avoided as it is available most statistical packages.

• This question is part of the following fields:

• Epidemiology And Statistics
59.1
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• #### Question 27 - What is the best study design to use when trying to determine a...

Incorrect

• What is the best study design to use when trying to determine a causal relationship between a certain factor and the onset of a rare disease?

Explanation:

Case control studies are used to determine the relationship between exposure to a risk factor and the resultant outcomes. It finds patients in the general population who have a certain condition and retrospectively searches for past exposure to possible risk factors for the disease. Controls are people who do not have the disease found in the general population. This type of study is useful for rare diseases, and is less time consuming to conduct. While cohort studies can be used to study rare diseases they measure the relative risk of developing the disease over time based on exposure. Ecological or cross-sectional studies attempt take a snapshot of a whole population, and thus are inappropriate for rare diseases as larger sample numbers are needed. A randomised control trial is better suited to determine the effect of an intervention.

• This question is part of the following fields:

• Epidemiology And Statistics
31.7
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• #### Question 28 - What is the primary reason for a written protocol? ...

Correct

• What is the primary reason for a written protocol?

Explanation:

A written protocol is important in clinical research as it helps to decrease bias with early findings as the process of the trial has been documented in advance. To show that the study has been properly undertaken before commencing, the investigators must document their names| they must describe the process, detail the analysis that will be undertaken, and provide a power calculation. The ethics committee does not always need to see the protocol.

• This question is part of the following fields:

• Epidemiology And Statistics
7
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• #### Question 29 - A screening test is found to have a sensitivity of 90% and a...

Correct

• A screening test is found to have a sensitivity of 90% and a specificity of 95%.Which of the following is the best answer?

Your Answer: An individual without disease is more likely to be correctly diagnosed via the test than someone with the disease

Explanation:

The sensitivity of a screening test can be described in a variety of ways, typically such as sensitivity being the ability of a screening test to detect a true positive, being based on the true positive rate, reflecting a test’s ability to correctly identify all people who have a condition, or, if 100%, identifying all people with a condition of interest by those people testing positive on the test.The specificity of a test is defined in a variety of ways, typically such as specificity is the ability of a screening test to detect a true negative, being based on the true negative rate, correctly identifying people who do not have a condition, or, if 100%, identifying all patients who do not have the condition of interest by those people testing negative on the test.

• This question is part of the following fields:

• Epidemiology And Statistics
15.1
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• #### Question 30 - For a given condition, disease or attribute, there will be a proportion of...

Incorrect

• For a given condition, disease or attribute, there will be a proportion of people in a population who have the given condition, disease or attribute at a specified point in time or over a specified period of time. Which of following is the best term which can describe the above?

Explanation:

Prevalence, sometimes referred to as prevalence rate, is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.

• This question is part of the following fields:

• Epidemiology And Statistics
36.1
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• #### Question 31 - A study of 500 men shows a significant correlation between their blood pressures...

Correct

• A study of 500 men shows a significant correlation between their blood pressures and weights (r = 0.45, P = 0.0014).Which one of the following is true?

Your Answer: There is a linear tendency for heavier men to have higher blood pressures

Explanation:

The main result of a correlation is called the correlation coefficient (or r). It ranges from -1.0 to +1.0. The closer r is to +1 or -1, the more closely the two variables are related.If r is close to 0, it means there is no relationship between the variables. If r is positive, it means that as one variable gets larger the other gets larger. If r is negative it means that as one gets larger, the other gets smaller (often called an inverse correlation).

• This question is part of the following fields:

• Epidemiology And Statistics
137.3
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• #### Question 32 - There is a measure of dispersion of a set of data from its...

Correct

• There is a measure of dispersion of a set of data from its mean. Which of following is the best term which can describe the above?

Explanation:

Standard deviation is defined as the measure of dispersion of a set of data from its mean. It measures the absolute variability of a distribution| the higher the dispersion or variability, the greater is the standard deviation and greater will be the magnitude of the deviation of the value from their mean.

• This question is part of the following fields:

• Epidemiology And Statistics
98
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• #### Question 33 - A clinical trial is conducted to study the benefits of a new oral...

Correct

• A clinical trial is conducted to study the benefits of a new oral medication to improve the symptoms of patients with asthma. In the trial 400 patients with asthma, half were given the new medication and half a placebo. Three months later they are asked to rate their symptoms using the following scale: much improved, slight improvement, no change, slight worsening, significantly worse. What is the most appropriate statistical test to see whether the new medication is beneficial?

Explanation:

The type of significance test used depends on whether the data is parametric (can be measured, usually normally distributed) or non-parametric.
Parametric tests:
Student’s t-test – paired or unpaired*
Pearson’s product-moment coefficient – correlation

Non-parametric tests:
Mann-Whitney U test – unpaired data
Wilcoxon signed-rank test – compares two sets of observations on a single sample
chi-squared test – used to compare proportions or percentages
Spearman, Kendall rank – correlation.

The outcome measured is not normally distributed, i.e. it is non-parametric. This excludes the Student’s t-tests. We are not comparing percentages/proportions so the chi-squared test is excluded. The Mann–Whitney U test is a nonparametric test of the null hypothesis that it is equally likely that a randomly selected value from one sample will be less than or greater than a randomly selected value from a second sample.
This test can be used to investigate whether two independent samples were selected from populations having the same distribution.

• This question is part of the following fields:

• Epidemiology And Statistics
73.6
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• #### Question 34 - In an age and sex matched case control study, 30 adolescents with high...

Correct

• In an age and sex matched case control study, 30 adolescents with high blood pressure were compared to 30 controls from the same clinic. The mean birth weights of the two groups were compared using a paired t-test. The results indicated that the control group was 150 g heavier with a standard error of 100 g.Which one of these is the most appropriate conclusion?

Your Answer: There is insufficient evidence to conclude whether or not birthweight affects the development of hypertension in adolescence

Explanation:

In case control studies, observational studies are made to compare two groups, individuals with a certain condition, to those without the condition, with all other factors being equal. In the situation presented by the question, the study was to determine whether a prior risk factor, a low birth weight, was associated with later developing adolescent hypertension, using a paired t-test to statistically determine whether there was indeed a significant association between the two conditions. Case control studies only help to draw associations between two groups and therefore cannot indicate causation. In this scenario we are also not given the p value to determine whether the association is statistically significant. Therefore there is not enough evidence to conclude whether or not birthweight affects the development of adolescent hypertension.

• This question is part of the following fields:

• Epidemiology And Statistics
157.1
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• #### Question 35 - In a double blind trial of a new diabetes medication, 25% more in...

Correct

• In a double blind trial of a new diabetes medication, 25% more in the treated group responded positively than those in the control group (95% CI 10% to 50%| P=0.004)

Explanation:

In the final result of this double blind study, 25% or one in four of patients who received the treatment responded positively. Though the difference is significant at P<0.05, it is better to present this as a significant difference at 0.4%. The number needed to treat (NNT) is defined as the inverse of the absolute risk reduction. Taking this as 0.25 (25%), the NNT is 1/0.25 = 4. However given the 95% confidence interval is between 10-50% for absolute risk reduction, the NNT with 95% CI is between 2 and 10. Therefore we cannot say with certainty that the NNT is at least 4.

• This question is part of the following fields:

• Epidemiology And Statistics
68.4
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• #### Question 36 - When sampling patients for a clinical trial the most important thing is that:...

Correct

• When sampling patients for a clinical trial the most important thing is that:

Explanation:

The selection process is based on five requirements and essentially aims to select a random representative cohort through:1.Isolating a group for which there is a greater or lesser chance of detecting a possible difference between the treatments compared|2.Establishing a homogeneous group in order to reduce the variability of response, thus making statistical comparison more sensitive and decreasing the risk of bias due to the constitution of non-homogeneous groups|3.Obtaining representative samples of the affection studied|4.Defining the rules corresponding to realistic recruitment|5.Respecting ethical obligations.

• This question is part of the following fields:

• Epidemiology And Statistics
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• #### Question 37 - A cohort study is developed to assess the correlation between blood pressure and...

Incorrect

• A cohort study is developed to assess the correlation between blood pressure and working long hours. After 10 years of follow-up and for the 1050 individuals working less than 40 hours per week, 1000 patients had normal blood pressure and 50 patients were diagnosed with hypertension. For the 660 patients working more than 40 hours per week, 600 patients had normal blood pressure and 60 patients were diagnosed with hypertension. If you work more than 40 hours per week, what is the odds ratio of developing hypertension compared to the individuals working less than 40 hours per week?

Explanation:

An odds ratio (OR) is a measure of the association between an exposure and an outcome. The OR represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure. Odds ratios are most commonly used in case-control studies, however they can also be used in cross-sectional and cohort study designs as well (with some modifications and/or assumptions). Wherea = Number of exposed casesb = Number of exposed non-casesc = Number of unexposed casesd = Number of unexposed non-casesOR=(a/c) / (b/d) = ad/bc

• This question is part of the following fields:

• Epidemiology And Statistics
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• #### Question 38 - Which of the following best describes odds ratios? ...

Correct

• Which of the following best describes odds ratios?

Your Answer: The odds of an event in one group divided by the odds of the event in another

Explanation:

Odds ratios are best described as the odds of an event in one group divided by the odds of the event in another. They form an alternative to the relative risk in case–control studies and are close to the relative risk when events are rare. The odds are the number of the event divided by the number without the event, which is less intuitive than the risk, which is the number with the event divided by the total. Odds ratios are therefore less intuitive than relative risks. Logistic regression analysis outputs variable coefficients which are the log of the odds ratio.

• This question is part of the following fields:

• Epidemiology And Statistics
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• #### Question 39 - Regarding consent to randomisation, which of the given statements is true? ...

Correct

• Regarding consent to randomisation, which of the given statements is true?

Your Answer: Should be obtained as part of the overall consent to the study

Explanation:

Randomization is one of the ethical protocols for research work, involving unbiased sample selection. Consent is required before undertaking any research and is taken for the complete research work at once. No separate consent is required for the process of randomization. The consent should explain each and every aspect of the study, including details about the process of randomization. Only particular study designs, like Zelen design, permit the avoidance of consent to randomization but these studies have their setbacks.

• This question is part of the following fields:

• Epidemiology And Statistics
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• #### Question 40 - A randomised controlled trial of a new treatment for hypertension yields a P-value...

Incorrect

• A randomised controlled trial of a new treatment for hypertension yields a P-value of 0.00036.Which one of the following gives the best interpretation of this information?

Correct Answer: To understand the clinical importance of the treatment we should also consider the confidence interval for the difference

Explanation:

The level of statistical significance is often expressed as a p-value between 0 and 1. The smaller the p-value, the stronger the evidence that you should reject the null hypothesis.A p-value less than 0.05 (typically ≤ 0.05) is statistically significant. It indicates strong evidence against the null hypothesis, as there is less than a 5% probability the null is correct (and the results are random). Therefore, we reject the null hypothesis, and accept the alternative hypothesis.However, this does not mean that there is a 95% probability that the research hypothesis is true. The p-value is conditional upon the null hypothesis being true is unrelated to the truth or falsity of the research hypothesis.A lower p-value is sometimes interpreted as meaning there is a stronger relationship between two variables. However, statistical significance means that it is unlikely that the null hypothesis is true (less than 5%).To understand the strength of the difference between two groups (control vs. experimental) a researcher needs to calculate the effect size.

• This question is part of the following fields:

• Epidemiology And Statistics
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