Biostatistics Flashcards

In a pharmacoeconomic study, incremental cost-effectiveness ratio (ICER) is calculated as $80,000 per QALY. Using the commonly cited US willingness-to-pay threshold, how should this be classified?

Answer: Borderline cost-effective

The conventional US WTP threshold is approximately $50,000–$150,000 per QALY; $80,000/QALY falls within this range, making it borderline or acceptable.

In a cohort study, person-years are used as the denominator for incidence rates. Why is this approach used?

Answer: It accounts for varying lengths of follow-up among participants

Person-years of observation account for the fact that participants may enter or exit the study at different times, ensuring the denominator reflects actual time at risk.

A publication reports a forest plot in which most individual study confidence intervals overlap zero, but the pooled diamond does not touch zero. What is the most accurate interpretation?

Answer: The pooled analysis has sufficient power to detect a statistically significant overall effect

Pooling studies in meta-analysis increases effective sample size, giving the pooled estimate greater power to detect effects that individual underpowered studies could not.

A researcher wants to assess agreement between two pharmacists measuring pill-cutting accuracy using a continuous scale. Which statistical method is most appropriate?

Answer: Bland-Altman plot and limits of agreement

The Bland-Altman method assesses agreement between two measurement methods by plotting the difference against the mean, revealing systematic bias and variability.

Cox proportional hazards regression produces a hazard ratio (HR) of 0.60 for a new antifungal vs. placebo (95% CI: 0.40–0.89). How should this be interpreted?

Answer: The new drug reduces the instantaneous risk of the event by 40% at any given time

HR < 1 means the treatment group has a lower instantaneous hazard; HR = 0.60 means a 40% reduction in the hazard of the event at any point in time.

Which study design provides the strongest evidence for establishing causality between a drug exposure and an outcome?

Answer: Randomized controlled trial

The RCT, through random allocation, minimizes confounding and allows for direct causal inference — it sits at the top of the hierarchy for intervention evidence.

In logistic regression used to predict a binary outcome (adverse drug reaction: yes/no), the model output is best expressed as:

Answer: An odds ratio derived from the exponentiated regression coefficient (e^β)

In logistic regression, exponentiating the β coefficient (e^β) yields the odds ratio for each one-unit increase in the predictor variable.