Biostatistics: Study Design & Analysis

What is a Type I error in hypothesis testing?

A Type I error (alpha) occurs when the null hypothesis is rejected when it is actually true, resulting in a false positive conclusion.

Define a double-blind study design.

A study where neither the participants nor the researchers interacting with them know which treatment group the participants are assigned to, minimizing observer and participant bias.

What does a p-value of < 0.05 typically indicate in biostatistics?

It indicates that the observed result is statistically significant, meaning there is less than a 5% probability the result occurred by chance alone under the null hypothesis.

What is the primary measure of association used in case-control studies?

The Odds Ratio (OR), which compares the odds of exposure in cases (those with the disease) to the odds of exposure in controls (those without).

In the hierarchy of evidence, which study design is considered the 'gold standard' for clinical interventions?

Randomized Controlled Trials (RCTs), as they minimize confounding and bias through random assignment.

What is the formula for Relative Risk (RR)?

RR = [Incidence in exposed group] / [Incidence in unexposed group].

Explain the difference between retrospective and prospective cohort studies.

Prospective cohorts follow a group forward in time from exposure to outcome, while retrospective cohorts use existing records to look back from a past exposure to the present outcome.

What is the purpose of Intention-to-Treat (ITT) analysis in an RCT?

ITT analyzes participants based on their initial group assignment regardless of whether they completed the treatment, preserving the benefits of randomization and preventing attrition bias.

How do you calculate the Number Needed to Treat (NNT)?

NNT = 1 / Absolute Risk Reduction (ARR), where ARR is the absolute difference in risk between the control and treatment groups.

When should a researcher use a Chi-square test instead of a t-test?

A Chi-square test is used for comparing categorical variables (proportions), whereas a t-test is used for comparing the means of continuous variables between two groups.