Primary Literature Evaluation - NAPLEX

1. What does it imply when a $95\%$ CI for a risk ratio includes $1$?

   Not statistically significant at $\alpha=0.05$. Inclusion of 1 in the $95\%$ CI for RR suggests no significant difference between groups, as it encompasses no effect.

2. What is the difference between intention-to-treat and per-protocol analyses?

   ITT analyzes as randomized; PP analyzes adherent completers. ITT preserves randomization by analyzing all participants in their assigned groups regardless of compliance, while PP focuses only on those who fully adhered to the protocol.

3. What is the definition of a confounder in primary literature evaluation?

   Factor associated with exposure and outcome, not on pathway. A confounder is an extraneous variable linked to both the exposure and outcome, potentially distorting the observed association if not controlled.

4. What is blinding (masking) primarily intended to reduce in clinical trials?

   Performance and detection (assessment) bias. Blinding minimizes biases where knowledge of treatment assignment could influence participant behavior or outcome evaluation by investigators.

5. Identify the NNH: CER $=0.05$ and EER $=0.10$ for an adverse event.

   $NNH=20$. With ARI as $0.10 - 0.05 = 0.05$, NNH is the reciprocal, meaning 20 patients treated to cause one extra adverse event.

6. What is a Type I error in hypothesis testing?

   Rejecting a true null hypothesis (false positive). A Type I error occurs when the null hypothesis is incorrectly rejected, leading to a false claim of a significant effect.

7. What is the formula for absolute risk reduction (ARR)?

   $ARR=\text{CER}-\text{EER}$. ARR measures the absolute difference in event rates between control and experimental groups, indicating the treatment's direct impact on risk.

8. Identify the ARR: CER $=0.30$ and EER $=0.24$ for the primary outcome.

   $ARR=0.06$. ARR is the difference in event rates, showing a $6\%$ absolute reduction in risk due to the intervention.

9. Identify the RR: CER $=0.25$ and EER $=0.20$ for the primary outcome.

   $RR=0.80$. RR is the ratio of event rates, indicating the experimental group has $80\%$ of the control group's risk.

10. What is a Type II error in hypothesis testing?

    Failing to reject a false null hypothesis (false negative). A Type II error happens when the null hypothesis is not rejected despite being false, missing a true effect.

11. What is the most appropriate analysis to preserve randomization benefits?

    Intention-to-treat analysis. ITT maintains the balance of confounders achieved through randomization by including all randomized participants in their original groups.

12. What is the formula for number needed to treat (NNT) when $ARR>0$?

    $NNT=\frac{1}{ARR}$. NNT represents the number of patients needing treatment to prevent one additional adverse outcome, based on the reciprocal of ARR.

13. Identify the NNT: CER $=0.20$ and EER $=0.10$ for the primary outcome.

    $NNT=10$. With ARR calculated as $0.20 - 0.10 = 0.10$, NNT is the reciprocal, indicating 10 patients treated to prevent one event.

14. What is the formula for number needed to harm (NNH) when $ARI>0$?

    $NNH=\frac{1}{ARI}$. NNH indicates the number of patients exposed to treatment to cause one additional harm, computed as the inverse of ARI.

15. What is the formula for absolute risk increase (ARI) for a harmful outcome?

    $ARI=\text{EER}-\text{CER}$. ARI quantifies the absolute increase in harmful event rate in the experimental group compared to control.

16. What is the primary purpose of randomization in a clinical trial?

    Balance known and unknown confounders between groups. Randomization distributes both measured and unmeasured confounding variables evenly across treatment groups to minimize bias in estimating treatment effects.

17. What is the formula for relative risk reduction (RRR)?

    $RRR=1-RR$. RRR expresses the proportional reduction in risk attributable to the treatment, derived from the relative risk.

18. What is the formula for relative risk (RR) in a parallel-group trial?

    $RR=\frac{\text{EER}}{\text{CER}}$. RR compares the probability of an event in the experimental group to the control group, providing a measure of relative effect size.

19. What is allocation concealment intended to prevent in randomized trials?

    Selection bias from predicting upcoming assignments. Allocation concealment ensures investigators cannot foresee treatment assignments, preventing selective enrollment that could introduce bias into group compositions.

20. What does it imply when a $95\%$ CI for a mean difference includes $0$?

    Not statistically significant at $\alpha=0.05$. Inclusion of 0 in the $95\%$ CI for mean difference indicates the possibility of no true difference, failing significance at $0.05$.

21. What is statistical power in a clinical study?

    $1-\beta$; probability of detecting a true effect. Power, denoted as $1-\beta$, represents the likelihood of correctly rejecting a false null hypothesis when a specific effect exists.

22. What does a $P$ value represent under the null hypothesis?

    Probability of results as or more extreme than observed. The $P$ value quantifies the probability of observing data at least as extreme as the actual results, assuming the null hypothesis is true.

23. What is the key limitation of subgroup analyses when not prespecified?

    High false-positive risk from multiple comparisons. Unplanned subgroup analyses increase the chance of Type I errors due to multiple testing without adjustments, leading to spurious findings.

24. What does a $95\%$ confidence interval represent in frequentist terms?

    $95\%$ of such intervals would contain the true value. In frequentist statistics, a $95\%$ CI means that if the experiment were repeated many times, $95\%$ of the calculated intervals would include the true population parameter.

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