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Question 1
Correct
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Which one of the following statements best describes a type II statistical error?
Your Answer: The null hypothesis is accepted when it is false
Explanation:In statistical hypothesis testing there are 2 types of errors:- type I: the null hypothesis is rejected when it is true – i.e. Showing a difference between two groups when it doesn’t exist, a false positive. – type II: the null hypothesis is accepted when it is false – i.e. Failing to spot a difference when one really exists, a false negative.
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 2
Correct
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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?
Your Answer: Mann-Whitney U test
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 – correlationNon-parametric tests:Mann-Whitney U test – unpaired dataWilcoxon signed-rank test – compares two sets of observations on a single samplechi-squared test – used to compare proportions or percentagesSpearman, 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.
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 3
Correct
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Which one of the following statements regarding epidemiological measures is correct?
Your Answer: Cross-sectional surveys can be used to estimate the prevalence of a condition in the population
Explanation:The incidence rate is the number of new cases per population at risk in a given time period. For example, if a population initially contains 1,000 non-diseased persons and 28 develop a condition over two years of observation, the incidence proportion is 28 cases per 1,000 persons per two years, i.e. 2.8% per two years.Prevalence is the proportion of a particular population found to be affected by a medical condition (typically a disease or a risk factor such as smoking or seat-belt use). It is derived by comparing the number of people found to have the condition with the total number of people studied, and is usually expressed as a fraction, as a percentage, or as the number of cases per 10,000 or 100,000 people.Incidence should not be confused with prevalence, which is the proportion of cases in the population at a given time rather than rate of occurrence of new cases. Thus, incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is.
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 4
Incorrect
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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?
Your Answer: 50/60
Correct Answer: 2
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
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 5
Correct
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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.
Your Answer: Chi squared (X²) test
Explanation:The Chi-squared test evaluates if two variables are related. The other statistical tests mentioned do not perform this function.
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 6
Incorrect
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A study is carried out to assess the efficacy of a rapid urine screening test developed to detect Chlamydia. The total number of people involved in the study were 200. The study compared the new test to the already existing NAAT techniques. The new test was positive in 20 patients that were Chlamydia positive and in 3 patients that were Chlamydia negative. For 5 patients that were Chlamydia positive and 172 patients that were Chlamydia negative the test turned out to be negative. Choose the correct value regarding the negative predictive value of the new test:
Your Answer: 20/23
Correct Answer: 172/177
Explanation:The definition of negative predictive value is the probability that the individuals with truly negative screening test don’t have Chlamydia. The equation is the following: Negative predictive value = Truly negative/(truly negative + false negative) = 172 / (172 + 5) = 172 / 177
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 7
Incorrect
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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?
Your Answer: 0.5
Correct Answer: 2.25
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
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 8
Incorrect
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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?
Your Answer: Probability
Correct Answer: Incidence
Explanation:Prevalence refers to the total number of cases of a particular disease or condition present in a population at a specific point in time or over a specified period. It provides a measure of how widespread the disease or condition is within the population.
Specificity and sensitivity are terms used to describe the accuracy of diagnostic tests.
Probability refers to the likelihood of an event occurring.
Incidence is a measure of how commonly or frequently a disease occurs in a specified population over a period by providing a quick measurement of new disease diagnoses.
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 9
Incorrect
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Which one of the following statements regarding the normal distribution is correct?
Your Answer: 99.7% of values lie within 2 standard deviations of the mean
Correct Answer: Mean = mode = median
Explanation:Normal distribution, also known as the Gaussian distribution, is a probability distribution that is symmetric about the mean. The normal distribution has the following properties:- It is symmetric around the mode, the median and the mean of the distribution.- It is unimodal- The area under the curve and over the x-axis is unity (i.e. equal to one).- Its density has two inflection points.- Its density is log-concave.The standard deviation (SD) is a measure of how much dispersion exists from the mean. SD = square root (variance)
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This question is part of the following fields:
- Medicine
- Research Skills
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Question 10
Incorrect
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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?
Your Answer:
Correct Answer: Standard deviation (root mean square deviation)
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.
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This question is part of the following fields:
- Medicine
- Research Skills
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SESSION STATS - PERFORMANCE PER SPECIALTY
