81. Topic: Cross-Sectional Study
Correct Answer: C. It is quick and require only one interview of study participants
Explanation: Cross-sectional studies are designed to capture a snapshot of a population at a single point in time, making them quick and requiring only one interview of study participants (A). They are valuable for planning and designing healthcare services by providing data on disease prevalence and care priorities (B, D). These studies also allow for the development of associations, which can generate hypotheses for future research (E). However, the statement “It is quick and require only one interview of study participants” (C) is redundant and incorrectly framed, as it repeats point A without adding any new information.
82. Topic: Disease Prevalence Factors
Correct Answer: D. Increased duration of illness
Explanation: Prevalence of a disease is influenced by factors affecting the number of existing cases. Emigration of affected cases (A) and higher cure rates (B) reduce the number of existing cases, thus decreasing prevalence. Increasing mortality rates (C) also lower the number of people living with the disease, reducing prevalence. A shorter duration of illness (E) means cases resolve quickly, leading to lower prevalence. However, an increased duration of illness (D) means individuals remain ill for longer periods, increasing the number of existing cases and thus raising the disease prevalence. Therefore, this is the factor that does not decrease disease prevalence.
83. Topic: Measurement of Health Conditions
Correct Answer: A. The number of people who have the health condition or disease and the size of the population at risk
Explanation: To compare the health conditions of different groups at any given time, it is essential to know both the number of people who have the health condition or disease and the size of the population at risk (A). This allows for calculating prevalence, a measure that indicates how widespread the condition is within a population. Relative risk (B, C) compares the risk between groups, and attributable risk (D) measures the difference in risk due to a specific factor, but neither provides a direct measure of the extent of health conditions across different groups. The population at risk alone (E) does not give information about the current number of cases, making it insufficient for this purpose.
84. Topic: Measurement of Disease Occurrence
Correct Answer: A. Cumulative incidence
Explanation: Cumulative incidence refers to the proportion of a population that develops a health condition or disease over a specific period of time. It is calculated by considering the number of new cases (numerator) and the size of the population at risk at the beginning of the study period (denominator), which aligns with the requirement of knowing the number of people who have the health condition or disease and the size of the population at risk (previous question). Instantaneous prevalence rate (B) measures the number of cases at a particular point in time, not over a period. Incidence rate (C) considers the occurrence of new cases in a dynamic population over a specified period, while “loto of prevalence” (D) is not a recognized epidemiological term. Thus, cumulative incidence (A) is the correct term for this measure.
85. Topic: Case-Control Study
Correct Answer: C. It is a quick and inexpensive to make
Explanation: Case-control studies are particularly effective for studying less common or rare conditions (A) and tend to be quicker and less expensive than cohort studies, making them often perceived as a cost-effective method (C). However, the statement “quick and inexpensive to make” may oversimplify the complexity and resource requirements sometimes involved in case-control studies. They do have limitations, such as cases being selective survivors (B), and they tend to support but not prove causal hypotheses by establishing associations (D). The number of subjects required to test a hypothesis of association in a case-control study is smaller than cross-sectional or cohort studies (E). Thus, while case-control studies are relatively quicker and less expensive, this does not universally apply to all cases, making option C a less definitive advantage.
86. Subject: Cohort study on the association between stroke and stress
Correct answer: D. Stress and stroke condition
Explanation: In a cohort study, the controlled variables are those that the researchers select and collect data on to examine their effect on the study results. In this specific study, the controlled variables are stress status (exposure) and stroke status (outcome). The other options (A, B, C, E) are not directly controlled in this particular cohort study of the association between stroke and stress.
87. Topic: Incidence of stroke in the stressed group
Correct answer: E. None of the above
Explanation: The incidence of stroke among the stressed group is calculated by dividing the number of stressed people who developed a stroke (300) by the total number of stressed people (1000). This gives an incidence of 30%, which corresponds to option A. However, the question asks which of the choices is incorrect, making “None of the above” (E) the correct answer for this question.
88. Topic: Incidence of stroke in the non-stressed group
Correct answer: E. None of the above
Explanation: The incidence of stroke in the non-stressed group is calculated by dividing the number of non-stressed people who developed a stroke (100) by the total number of non-stressed people (1000). This gives an incidence of 10%, which is not represented among the choices offered, making “None of the above” (E) the correct answer.
89. Topic: Relative risk of stroke in stressed individuals
Correct answer: B. 3
Explanation: The relative risk (RR) is calculated by dividing the incidence of stroke in stressed people by the incidence in non-stressed people. The incidence in stressed people is 30% (300/1000) and in non-stressed people 10% (100/1000). RR = 30% / 10% = 3. This means that people under stress are 3 times more likely to develop a stroke than people not under stress.
90. Topic: Attributable risk of stroke in people under stress
Correct answer: C. 20
Explanation: The attributable risk (AR) is calculated by subtracting the incidence of stroke in non-stressed people from the incidence in stressed people. The incidence in stressed people is 30% (300/1000) and in non-stressed people 10% (100/1000). So, RA = 30% – 10% = 20%. This means that 20% of strokes in stressed people can be attributed to stress.
- Topic: Evaluation of Procedures
Correct Answer: A. The validity
Explanation: When evaluating a newly developed procedure against a standard procedure, the primary concern is the validity (A), which refers to how well the new procedure measures what it is intended to measure and its accuracy in comparison to the standard. Reliability (B) refers to the consistency of the procedure, not its comparative accuracy. While both validity and reliability (C) are important for overall assessment, the specific task of comparing a new procedure to a standard one is primarily focused on validity. Plausibility (D) is about the reasonableness or credibility of a procedure, which is not the focus in this context. Thus, the correct term for this comparison is validity.
- Topic: Evaluation of Questionnaire Responses
Correct Answer: B. Reliability
Explanation: Comparing responses to a new questionnaire obtained one month apart assesses the reliability (B) of the questionnaire. Reliability refers to the consistency and stability of the responses over time. If the responses are similar across the two occasions, the questionnaire is considered reliable. Validity (A) concerns whether the questionnaire measures what it is supposed to measure, which is not directly assessed by repeated administration. Precision (D) involves the exactness of the measurements, and is not the primary focus here. Therefore, the correct measure being assessed in this scenario is reliability.
- Topic: Sensitivity and Specificity
Correct Answer: E. Predictive value
Explanation: Sensitivity and specificity are critical parameters for assessing the performance of a diagnostic test. They contribute to the calculation of the predictive values (E), which determine the likelihood that a person with a positive test result actually has the disease (positive predictive value) or that a person with a negative test result is disease-free (negative predictive value). Validity (A) broadly refers to the accuracy of a test, which involves both sensitivity and specificity, but predictive values specifically express this accuracy in practical terms. Reliability (B) pertains to the consistency of test results, not to sensitivity and specificity. Thus, the term expressed in terms of sensitivity and specificity is predictive value.
- Topic: Bias in Cohort Studies
Correct Answer: A. The lost sight
Explanation: The most concerning common type of bias in cohort studies is “the lost sight” (A), also known as loss to follow-up bias. This occurs when participants drop out of the study over time, potentially leading to non-representative results if the reasons for dropout are related to the exposure or outcome. Random classification error (B) and confusion bias (D), often referred to as confounding, are important but typically less impactful in cohort studies compared to loss to follow-up. Thus, loss to follow-up is a primary concern due to its potential to significantly affect study validity.
- Topic: P-value in Statistical Testing
Correct Answer: D. The sample size of the study population can affect the size of the p-value
Explanation: The statement that is not true of a p-value is D. The sample size of the study population does affect the precision of estimates and the width of confidence intervals, but it does not directly affect the size of the p-value itself. P-values are primarily influenced by the magnitude of the difference observed between study groups (C) and indicate the strength of evidence against the null hypothesis. A lower p-value (typically < 0.05) suggests stronger evidence against the null hypothesis and that the observed result is unlikely to be due to chance. Therefore, the correct answer to the question is D.
- Topic: Restriction in Study Design
Correct Answer: C. The restriction does not establish the association between exposure and disease for different exposure factors
Explanation: Restriction is a technique used to control for confounding factors by limiting the study population to those who meet specific criteria related to the confounder. However, it does not directly establish the association between exposure and disease for different levels of exposure factors (C). Instead, restriction aims to reduce confounding by restricting the study population to a more homogeneous group regarding potential confounders. Option A correctly states that restriction may reduce the number of eligible subjects (A), and option B acknowledges that residual confounding can occur if the criteria for restriction are not narrow enough (B). Option D suggests that restriction improves validity by reducing bias from confounding factors (D). Therefore, the statement that is not true about restriction is C.
- Topic: Bradford Hill Criteria for Disease Causation
Correct Answer: E. The stability of the association
Explanation: The Bradford Hill criteria are used to assess the likelihood of a causal relationship between an exposure and a disease. The stability of the association (E) refers to whether the association between the exposure and the disease remains consistent over time or under varying conditions. While it is considered in evaluating causation, it is generally considered less crucial compared to other criteria such as the strength of association (B), biological gradient (A), specificity (C), and temporal relationship (D). These criteria provide more direct evidence of causality or the mechanisms involved in disease causation.
- Topic: Experimental Study vs. Observational Study
Correct Answer: E. Investigators determine who is and who is not exposed to the suspected causative factor
Explanation: The key difference between an experimental study and an observational study lies in how exposure to the suspected causative factor is determined. In an experimental study (E), investigators actively assign participants to either be exposed or not exposed to the factor of interest. This assignment allows for controlled testing of hypotheses and causal relationships. Conversely, in observational studies (A and C), researchers observe individuals who are already exposed or unexposed based on natural circumstances or historical data, without intervention. Experimental studies are typically prospective (A) in nature because they involve following participants forward in time from exposure to outcome, whereas retrospective studies (B and C) look backward at exposures and outcomes that have already occurred.
- Topic: Type of graph to illustrate the decline in gonorrhoea rates in the region over the last 10 years
Correct Answer: E. Line diagram
Explanation: A line diagram, also known as a line graph, is the most suitable choice for illustrating trends over time, such as the decline in gonorrhea rates for both men and women over the past 10 years. Line graphs effectively show changes and trends in data points connected by lines, making them ideal for visualizing how rates have changed over time. They allow for easy comparison between different groups (men and women in this case) and provide a clear representation of the trend in gonorrhea rates over the specified period. Therefore, option E, the line diagram, is the best choice to present this type of temporal data to the public health board.
- Topic: Disadvantages of a Crossover Trial
Correct Answer: D. All of the above answers
Explanation: In a crossover trial, subjects may experience disadvantages such as: Subjects who respond to the treatment being tested are removed from it and given a placebo or an alternative treatment, which can affect the continuity of treatment effects. The washout period with some drugs can be quite long during which patients are given a placebo, potentially prolonging the trial duration and introducing variability. It cannot be used if the treatment has permanent effects, limiting its applicability to treatments that can be withdrawn without lasting effects. Therefore, all the options provided in answer D highlight the potential disadvantages of crossover trials, making it the correct choice.