What type of data is represented by categories such as male or female?
a) Nominal
b) Ordinal
c) Interval
d) Ratio
Answer: a) Nominal
Explanation: Nominal data are categories without a logical order, such as gender or race.

Which measure of central tendency is preferred for normally distributed continuous data?
a) Mean
b) Median
c) Mode
d) Range
Answer: a) Mean
Explanation: The mean is the average and best represents normally distributed continuous data.

What is the median of the following scores: 75, 82, 90, 92, 67, 95, 110, 80, 82, 86?
a) 82
b) 84
c) 90
d) 110
Answer: b) 84
Explanation: Arrange the scores in order: 67, 75, 80, 82, 82, 86, 90, 92, 95, 110. The median is the average of the 5th and 6th values: (82+86)/2 = 84.

Which statistical test is appropriate for comparing means between two independent groups?
a) Chi-square test
b) T-test
c) ANOVA
d) Correlation
Answer: b) T-test
Explanation: The t-test compares means between two groups when data are continuous and normally distributed.

What does a p-value less than 0.05 indicate?
a) The null hypothesis is accepted
b) The results are statistically significant
c) The sample size is too small
d) The results are due to chance
Answer: b) The results are statistically significant
Explanation: A p-value < 0.05 suggests that the observed effect is unlikely due to chance.

If the incidence of heart attack is 2% in the treatment group and 7% in the control group, what is the Absolute Risk Reduction (ARR)?
a) 5%
b) 9%
c) 2%
d) 7%
Answer: a) 5%
Explanation: ARR = Control event rate – Treatment event rate = 7% – 2% = 5%.

What is the Number Needed to Treat (NNT) if the ARR is 5%?
a) 5
b) 10
c) 20
d) 25
Answer: c) 20
Explanation: NNT = 1 / ARR = 1 / 0.05 = 20.

Which data transformation is most commonly used in medical research?
a) Logarithmic
b) Square root
c) Reciprocal
d) Ratio
Answer: a) Logarithmic
Explanation: Log transformation is frequently used to normalize skewed data.

What type of variable is a pain scale with categories like mild, moderate, and severe?
a) Nominal
b) Ordinal
c) Interval
d) Ratio
Answer: b) Ordinal
Explanation: Ordinal data have a logical order but unequal intervals between categories.

Which of the following best describes the standard deviation (SD)?
a) The average value of the data
b) The spread of data around the mean
c) The middle value of the data set
d) The difference between highest and lowest values
Answer: b) The spread of data around the mean
Explanation: SD measures variability or dispersion of data points from the mean.

What does a hazard ratio (HR) of 1 indicate?
a) Treatment is harmful
b) No difference between treatment and control
c) Treatment is beneficial
d) Data is invalid
Answer: b) No difference between treatment and control
Explanation: HR = 1 means equal risk in both groups.

Which test is used to assess the association between two categorical variables?
a) T-test
b) Chi-square test
c) ANOVA
d) Correlation
Answer: b) Chi-square test
Explanation: Chi-square tests for independence between categorical variables.

What is the mode of the following data: 75, 82, 90, 92, 67, 95, 110, 80, 82, 86?
a) 75
b) 82
c) 90
d) 86
Answer: b) 82
Explanation: Mode is the most frequently occurring value.

Which measure is preferred for skewed continuous data?
a) Mean
b) Median
c) Mode
d) Range
Answer: b) Median
Explanation: Median is less affected by outliers and skewed data.

What does a confidence interval (CI) represent?
a) The range of values within which the true population parameter lies with a certain level of confidence
b) The probability that the null hypothesis is true
c) The average of the sample data
d) The p-value of a test
Answer: a) The range of values within which the true population parameter lies with a certain level of confidence
Explanation: CI provides an estimated range likely to include the true parameter.

If the odds ratio (OR) is less than 1, what does it indicate?
a) Increased odds of outcome with exposure
b) Decreased odds of outcome with exposure
c) No association
d) Invalid data
Answer: b) Decreased odds of outcome with exposure
Explanation: OR < 1 suggests the exposure reduces the odds of the outcome.

Which of the following is NOT a measure of variability?
a) Range
b) Variance
c) Standard deviation
d) Mean
Answer: d) Mean
Explanation: Mean is a measure of central tendency, not variability.

What does a p-value of 0.20 indicate about the study results?
a) Statistically significant
b) Not statistically significant
c) Strong evidence against the null hypothesis
d) Data error
Answer: b) Not statistically significant
Explanation: p-value > 0.05 generally means insufficient evidence to reject the null hypothesis.

Which of the following best describes interval data?
a) Data with categories only
b) Data with meaningful zero point
c) Data with ordered categories but unequal intervals
d) Data with equal intervals but no true zero
Answer: d) Data with equal intervals but no true zero
Explanation: Interval data have equal spacing but lack an absolute zero (e.g., temperature in Celsius).

How is relative risk reduction (RRR) calculated?
a) (Control event rate – Treatment event rate) / Control event rate
b) Treatment event rate – Control event rate
c) Control event rate / Treatment event rate
d) Treatment event rate / Control event rate
Answer: a) (Control event rate – Treatment event rate) / Control event rate
Explanation: RRR expresses the proportional reduction in risk between groups.

What is the primary purpose of a randomized controlled trial (RCT)?
a) To observe natural disease progression
b) To eliminate bias by randomly assigning participants to groups
c) To collect qualitative data
d) To analyze retrospective data
Answer: b) To eliminate bias by randomly assigning participants to groups
Explanation: RCTs use randomization to evenly distribute confounding factors and reduce selection bias.

Which of the following is an example of a continuous variable?
a) Blood type
b) Number of hospital visits
c) Body temperature
d) Smoking status
Answer: c) Body temperature
Explanation: Continuous variables can take any value within a range, like temperature.

What does a specificity of 90% mean in a diagnostic test?
a) 90% of diseased patients test positive
b) 90% of healthy patients test negative
c) 10% of diseased patients test negative
d) 10% of healthy patients test positive
Answer: b) 90% of healthy patients test negative
Explanation: Specificity is the ability of a test to correctly identify those without the disease.

If a study reports a Relative Risk (RR) of 2.0, what does this mean?
a) The risk in the treatment group is twice that of the control group
b) The risk in the control group is twice that of the treatment group
c) No difference in risk between groups
d) The treatment reduces risk by 50%
Answer: a) The risk in the treatment group is twice that of the control group
Explanation: RR > 1 indicates increased risk in the exposed group compared to control.

Which of the following best describes a Type I error?
a) Failing to reject a false null hypothesis
b) Rejecting a true null hypothesis
c) Incorrectly accepting the alternative hypothesis
d) None of the above
Answer: b) Rejecting a true null hypothesis
Explanation: Type I error is a false positive, concluding an effect exists when it does not.

What does a confidence interval (CI) that includes 1 mean for an odds ratio (OR)?
a) The result is statistically significant
b) The result is not statistically significant
c) The OR is exactly 1
d) The sample size is large
Answer: b) The result is not statistically significant
Explanation: If the CI includes 1, the effect could be null, indicating no significant association.

Which statistical test would you use to compare the means of three or more groups?
a) T-test
b) Chi-square test
c) ANOVA
d) Correlation
Answer: c) ANOVA
Explanation: ANOVA tests for differences among three or more group means.

What is the purpose of blinding in clinical trials?
a) To increase sample size
b) To reduce bias by preventing participants or researchers from knowing group assignments
c) To randomize participants
d) To improve statistical power
Answer: b) To reduce bias by preventing participants or researchers from knowing group assignments
Explanation: Blinding minimizes placebo effects and observer bias.

Which of the following is NOT a measure of central tendency?
a) Mean
b) Median
c) Mode
d) Variance
Answer: d) Variance
Explanation: Variance measures variability, not central tendency.

What does a correlation coefficient (r) of -0.8 indicate?
a) Strong positive correlation
b) Strong negative correlation
c) Weak positive correlation
d) No correlation
Answer: b) Strong negative correlation
Explanation: Negative values indicate inverse relationships; -0.8 is a strong negative correlation.

Which of the following is an example of a nominal variable?
a) Blood pressure
b) Eye color
c) Weight
d) Temperature
Answer: b) Eye color
Explanation: Nominal variables are categories without order.

What is the difference between prevalence and incidence?
a) Prevalence measures new cases; incidence measures total cases
b) Prevalence measures total cases; incidence measures new cases
c) Both measure new cases
d) Both measure total cases
Answer: b) Prevalence measures total cases; incidence measures new cases
Explanation: Prevalence is the proportion of existing cases; incidence is the rate of new cases over time.

Which of the following best describes a Type II error?
a) Rejecting a true null hypothesis
b) Failing to reject a false null hypothesis
c) Accepting a false alternative hypothesis
d) None of the above
Answer: b) Failing to reject a false null hypothesis
Explanation: Type II error is a false negative, missing a real effect.

What does the term “power” of a study refer to?
a) Probability of making a Type I error
b) Probability of correctly rejecting a false null hypothesis
c) Probability of making a Type II error
d) Sample size
Answer: b) Probability of correctly rejecting a false null hypothesis
Explanation: Power reflects the study’s ability to detect a true effect.

Which of the following is the best measure to use when the outcome is rare?
a) Relative risk
b) Odds ratio
c) Absolute risk reduction
d) Number needed to treat
Answer: b) Odds ratio
Explanation: Odds ratios are often used in case-control studies and rare outcomes.

What is the formula for calculating relative risk (RR)?
a) (Risk in treatment group) / (Risk in control group)
b) (Risk in control group) / (Risk in treatment group)
c) (Risk in treatment group) – (Risk in control group)
d) (Risk in control group) – (Risk in treatment group)
Answer: a) (Risk in treatment group) / (Risk in control group)
Explanation: RR compares the probability of an event between two groups.

Which of the following biases occurs when participants drop out of a study?
a) Selection bias
b) Attrition bias
c) Recall bias
d) Observer bias
Answer: b) Attrition bias
Explanation: Attrition bias arises from systematic differences due to loss of participants.

What does a wide confidence interval indicate?
a) High precision
b) Low precision
c) Statistically significant result
d) Large sample size
Answer: b) Low precision
Explanation: Wide CIs suggest more uncertainty about the estimate.

Which of the following is an example of interval data?
a) Temperature in Celsius
b) Number of hospital visits
c) Blood type
d) Pain scale (mild, moderate, severe)
Answer: a) Temperature in Celsius
Explanation: Interval data have equal intervals but no true zero.

What does an odds ratio (OR) of 1.5 mean?
a) 50% increased odds of outcome with exposure
b) 50% decreased odds of outcome with exposure
c) No association
d) Outcome is twice as likely in control group
Answer: a) 50% increased odds of outcome with exposure
Explanation: OR > 1 indicates higher odds of the outcome in the exposed group.

What does the term “bias” refer to in clinical research?
a) Random error in data collection
b) Systematic error that leads to incorrect conclusions
c) Variation due to chance
d) Large sample size
Answer: b) Systematic error that leads to incorrect conclusions
Explanation: Bias is a systematic deviation from the truth, affecting validity.

Which study design is best suited to determine the cause of a rare disease?
a) Randomized controlled trial
b) Cohort study
c) Case-control study
d) Cross-sectional study
Answer: c) Case-control study
Explanation: Case-control studies are efficient for studying rare diseases by comparing cases and matched controls.

What is the primary advantage of a double-blind study?
a) Larger sample size
b) Reduced selection bias
c) Reduced placebo and observer bias
d) Faster data collection
Answer: c) Reduced placebo and observer bias
Explanation: Double-blinding prevents both participants and researchers from knowing group assignments, minimizing bias.

Which of the following is NOT a characteristic of a cohort study?
a) Observational design
b) Participants selected based on exposure status
c) Randomization of participants
d) Can measure incidence
Answer: c) Randomization of participants
Explanation: Cohort studies are observational and do not involve randomization.

What does a p-value of 0.001 imply?
a) There is a 0.1% chance the null hypothesis is true
b) The results are highly statistically significant
c) The sample size is too small
d) The null hypothesis is accepted
Answer: b) The results are highly statistically significant
Explanation: A very low p-value indicates strong evidence against the null hypothesis.

Which measure of central tendency is most affected by outliers?
a) Mean
b) Median
c) Mode
d) Range
Answer: a) Mean
Explanation: The mean is sensitive to extreme values, unlike the median or mode.

What is the purpose of stratification in clinical trials?
a) To increase sample size
b) To control for confounding variables
c) To randomize participants
d) To reduce measurement error
Answer: b) To control for confounding variables
Explanation: Stratification ensures balanced distribution of confounders across groups.

Which of the following best describes a cross-sectional study?
a) Follows participants over time to assess outcomes
b) Assesses exposure and outcome at a single point in time
c) Randomly assigns participants to interventions
d) Compares cases with controls retrospectively
Answer: b) Assesses exposure and outcome at a single point in time
Explanation: Cross-sectional studies provide a snapshot of data at one time.

What does the term “intention-to-treat” analysis mean?
a) Only participants who complete the study are analyzed
b) Participants are analyzed according to the group they were originally assigned
c) Participants who drop out are excluded from analysis
d) Only participants who respond to treatment are analyzed
Answer: b) Participants are analyzed according to the group they were originally assigned
Explanation: Intention-to-treat preserves randomization and reduces bias.

Which of the following is true about the null hypothesis?
a) It states there is an effect or difference
b) It is accepted when p < 0.05
c) It is a statement of no effect or no difference
d) It is only used in observational studies
Answer: c) It is a statement of no effect or no difference
Explanation: The null hypothesis assumes no relationship between variables.