Welcome to your 📊 Epidemiology & Biostatistics Arena — 60 Integrated MCQs
1.
Twenty patients have serum sodium measured before and after an intervention. A paired t test is planned. What quantity is principally analyzed by this test?
2.
A trial compares mean recovery time between two treatments. The estimated mean difference is 2.2 days, with a 95% confidence interval from −1.2 to 5.6 days. Which interpretation is most appropriate?
3.
A population has a known mean serum value of 100 units and a standard deviation of 12 units. A sample of 36 patients has a mean of 104 units. What is the Z statistic?
4.
A researcher studies a small sample in which the population standard deviation is unknown. Compared with the standard normal distribution, why does the t distribution require more extreme critical values when degrees of freedom are low?
5.
A researcher reports only the range for a dataset containing 200 observations. A reviewer states that this gives limited information about overall variability. What is the main reason?
6.
A case-control study investigates an association between a dietary exposure and renal disease. Age is related to both dietary exposure and renal disease. The investigators want to reduce this distortion while selecting controls. Which method is most appropriate?
7.
A two-sided Z test is performed at α = 0.05. The calculated Z value is +2.30, and the critical values are approximately −1.96 and +1.96. What is the correct decision?
8.
Following one confirmed case of an infectious illness in a household, investigators assess how many susceptible household contacts subsequently develop the illness. Which measure best evaluates this spread?
9.
A preventive intervention is tested by randomly allocating eligible participants to intervention and control groups. What is the main epidemiological advantage of random allocation?
10.
A screening programme is designed so that individuals without the target disease are rarely classified as positive. Which characteristic of the test has been emphasized?
11.
A child's height lies at the 90th percentile of a reference distribution. Which interpretation is most appropriate?
12.
In a survey, headache severity scores are distributed as follows: score 1 in 4 students, score 2 in 6 students, score 3 in 10 students and score 4 in 5 students. Which approach is required to calculate the arithmetic mean correctly?
13.
Investigators studying a difficult-to-reach population recruit several initial participants and ask each participant to identify other eligible individuals. Which sampling technique is being used?
14.
A questionnaire categorizes some exposed participants as unexposed because the exposure questions are poorly defined. Which methodological problem is most directly illustrated?
15.
A dataset initially contains values tightly clustered around its mean. One extremely high value is then added. Which pair of statistics is likely to be most directly increased by this new observation?
16.
A community study finds a statistically significant chi-square association between a dietary habit and hypertension. Which conclusion is most appropriate?
17.
A researcher collects newly measured blood-pressure readings specifically for a community survey rather than using previously recorded hospital information. How should these measurements be classified?
18.
A survey conducted on 1 September identifies all adults who have chronic kidney disease on that particular day. Which epidemiological measure is being estimated?
19.
A researcher summarizes fasting glucose values using the mean and standard deviation. Inspection of the frequency graph shows a marked right-sided tail caused by several unusually high values. Which change would improve the descriptive summary?
20.
A district health team surveys adults during one week and records both current analgesic use and the presence of chronic kidney disease. An association is found between the two variables. Which limitation most restricts interpretation of this finding?
21.
Researchers classify pain severity as mild, moderate or severe before comparing two groups. Which description best fits this variable?
22.
Two wards have the same average duration of hospital stay. In Ward A, most patients stay close to the average, whereas Ward B includes many very short and very long admissions. Which statistical feature is expected to be greater in Ward B?
23.
A dataset contains 100 observations. After ordering the values, a researcher identifies the values corresponding to the 25th and 75th percentiles. What information is obtained directly from the difference between these two values?
24.
A researcher plots a perfectly symmetrical bell-shaped distribution. Most observations lie near the centre and progressively fewer observations occur toward either tail. Which interpretation best explains the importance of the graph?
25.
An equal-variance independent-samples t test compares 15 patients receiving treatment A with 17 separate patients receiving treatment B. What are the degrees of freedom?
26.
Participants in a cohort contribute different lengths of follow-up because some enter the study late and others leave early. The investigators want to relate new cases to the actual observation time contributed by participants. Which approach is most appropriate?
27.
A national survey first randomly selects districts, then health facilities within those districts, and finally patients within the selected facilities. Which sampling method best describes this process?
28.
Two districts report the same number of deaths from chronic kidney disease. District A has a much larger population than District B. Which measure is most appropriate for comparing the population burden of death from this disease?
29.
A frequency distribution is symmetrical and unimodal. Its mean is 50. Which additional finding would most strongly support that the distribution is normal?
30.
The same screening test is used in two populations. Disease is much more common in Population X than in Population Y. Sensitivity and specificity remain unchanged. Which result is most likely in Population X?
31.
A student uses SPSS to analyze a clinical dataset. Sex, smoking status and disease status are entered as numerical codes, and the student treats all three as continuous measurements because SPSS displays numbers. What is the most appropriate correction?
32.
Two normal distributions have the same standard deviation but different means. How will their graphs primarily differ?
33.
A health department reports that 18% of all deaths registered during one year were due to cardiovascular disease. What can be concluded from this figure?
34.
A community medicine researcher records systolic blood pressure in five adults as 110, 116, 120, 124 and 180 mmHg. The researcher wants a single value that best represents the typical blood pressure without being disproportionately influenced by the extreme observation. Which measure should be reported?
35.
A small clinical study finds no statistically significant difference between two rehabilitation methods. The investigators suspect that the study had inadequate power. Which interpretation is most appropriate?
36.
A two-sided Z test gives Z = 2.00. The corresponding P value is approximately 0.046. Which conclusion is most appropriate?
37.
A dataset contains the ordered values 8, 10, 12, 14, 16 and 18. Which value represents the median of this dataset?
38.
A research team changes its significance level from 0.05 to 0.01 without changing sample size or study design. Which effect is most likely?
39.
A researcher calculates variance for a set of body-weight measurements recorded in kilograms. Which feature makes standard deviation easier to interpret than variance?
40.
A researcher plans to increase the sample size from 100 to 400 participants while expecting a similar standard deviation. What will happen approximately to the standard error of the mean?
41.
A linear regression model relating age to systolic blood pressure is written as: predicted systolic blood pressure = 95 + 0.7 × age. How should the coefficient 0.7 be interpreted?
42.
Hospital length of stay has a long right tail because a small number of patients remain admitted for several weeks. The researcher wishes to select an analysis method that is less dependent on normal-distribution assumptions. Which approach is most appropriate?
43.
Two independent groups of patients rate postoperative discomfort on an ordered scale. The observations are markedly skewed and do not satisfy assumptions for a standard parametric comparison. Which statistical approach is most appropriate?
44.
A box-and-whisker plot shows Q1 at 22 and Q3 at 38. Which value represents the spread of the central half of the observations?
45.
A health survey reports median household expenditure together with Q1 and Q3 because the data are markedly skewed. Which additional statistic can be calculated directly from the reported quartiles?
46.
A laboratory screening test gives almost identical results when repeated on the same specimens, but comparison with the reference method shows that the values are consistently inaccurate. Which property best describes this test?
47.
In a study comparing two treatment groups, the assessor knows which treatment each participant received and unconsciously rates improvement more favourably in one group. Which measure would best reduce this source of error?
48.
Two countries have markedly different crude death rates. Country X has a substantially older population than Country Y. The health analyst wants a fairer comparison of mortality between the countries. Which epidemiological approach is most appropriate?
49.
A researcher wants to describe variability in an approximately symmetrical set of hemoglobin values. Which feature makes standard deviation preferable to range for this purpose?
50.
A research team compares variability in serum sodium and body weight. The measurements have different numerical scales and different means. Which statistic would provide the most appropriate comparison of their relative variability?
51.
A research team finds a difference in disease frequency between two groups and wants to determine whether the observed difference could reasonably reflect random variation rather than a true population difference. Which discipline provides the methods needed for this assessment?
52.
A normally distributed biological measurement has a mean of 100 units and a standard deviation of 10 units. Approximately what proportion of observations would be expected between 80 and 120 units?
53.
A researcher measures mean fasting blood glucose in a sample and obtains a mean of 80 mg/dL with a standard error of 2 mg/dL. Using 1.96 as the critical value, which is the approximate 95% confidence interval?
54.
Researchers compare average air-pollution levels and respiratory-disease mortality across several cities. Cities with greater pollution have higher mortality. Which interpretation is most appropriate?
55.
In a contingency table, one row contains 80 participants, one column contains 60 participants, and the grand total is 200. Under the null hypothesis of independence, what is the expected frequency for their intersecting cell?
56.
A dataset of waiting times is positively skewed. After several very long waiting times are removed, the distribution becomes much more symmetrical. Which relationship is now more likely?
57.
A researcher reports a strong Pearson correlation between two laboratory measurements. Inspection of the scatterplot shows that most observations have little relationship, but one extreme value strongly influences the fitted pattern. What should be concluded?
58.
A public-health officer compares two datasets with identical means. Dataset X has an SD of 3 units and Dataset Y has an SD of 12 units. Which graphical appearance is most consistent with Dataset Y if both are approximately normally distributed?
59.
A researcher applies a chi-square test to a small contingency table. Several expected cell frequencies are very low. What is the main statistical concern?
60.
A large hospital study finds that a new intervention reduces mean systolic blood pressure by 1 mmHg compared with standard care, with P = 0.001. Which conclusion is most appropriate?
