A group of investigators seeks to compare the non-inferiority of a new angiotensin receptor blocker, salisartan, with losartan for reduction of blood pressure. 2,000 patients newly diagnosed with hypertension are recruited for the trial; the first 1,000 recruited patients are administered losartan, and the other half are administered salisartan. Patients with a baseline systolic blood pressure less than 100 mmHg are excluded from the study. Blood pressure is measured every week for four weeks, with the primary outcome being a reduction in systolic blood pressure by salisartan within 10% of that of the control. Secondary outcomes include incidence of subjective improvement in symptoms, improvement of ejection fraction, and incidence of cough. 500 patients withdraw from the study due to symptomatic side effects. In an intention-to-treat analysis, salisartan is deemed to be non-inferior to losartan for the primary outcome but inferior for all secondary outcomes. As the investigators launch a national advertising campaign for salisartan, independent groups report that the drug is inferior for its primary outcome compared to losartan and associated with respiratory failure among patients with pulmonary hypertension. How could this study have been improved?

Posthoc analysis of primary outcome among patients who withdrew from study

Retrial of primary outcome for clinical effectiveness instead of non-inferiority

A 57-year-old man presents to his oncologist to discuss management of small cell lung cancer. The patient is a lifelong smoker and was diagnosed with cancer 1 week ago. The patient states that the cancer was his fault for smoking and that there is "no hope now." He seems disinterested in discussing the treatment options and making a plan for treatment and followup. The patient says "he does not want any treatment" for his condition. Which of the following is the most appropriate response from the physician?

"It must be very challenging having received this diagnosis. I want to work with you to create a plan."

"You seem upset at the news of this diagnosis. I want you to go home and discuss this with your loved ones and come back when you feel ready to make a plan together for your care."

"It must be tough having received this diagnosis; however, new cancer therapies show increased efficacy and excellent outcomes."

"We are going to need to treat your lung cancer. I am here to help you throughout the process."

"I respect your decision and we will not administer any treatment. Let me know if I can help in any way."

You submit a paper to a prestigious journal about the effects of coffee consumption on mesothelioma risk. The first reviewer lauds your clinical and scientific acumen, but expresses concern that your study does not have adequate statistical power. Statistical power refers to which of the following?

The probability of detecting an association when an association does exist.

The probability of detecting an association when no association exists.

The probability of not detecting an association when an association does exist.

The square root of the variance.

In the study, all participants who were enrolled and randomly assigned to treatment with pulmharkimab were analyzed in the pulmharkimab group regardless of medication nonadherence or refusal of allocated treatment. A medical student reading the abstract is confused about why some participants assigned to pulmharkimab who did not adhere to the regimen were still analyzed as part of the pulmharkimab group. Which of the following best reflects the purpose of such an analysis strategy?

To assess treatment efficacy more accurately

To increase internal validity of study

Per-protocol analysis for USMLE Step 2 CK: High-Yield Biostatistics Lessons

Per-Protocol Analysis - The Perfect Patient Run

Per-protocol (PP) analysis, also known as on-treatment or efficacy analysis, evaluates only participants who strictly adhere to the clinical trial's rules. It aims to measure the treatment's effect under ideal conditions.
Core Principle: Includes only patients with high compliance (e.g., took >80% of doses). This is the opposite of Intention-to-Treat (ITT) analysis, which includes all randomized subjects regardless of adherence.

⭐ Per-protocol analysis estimates the effect of an intervention under ideal, or 'perfect', conditions, answering the question: 'What is the maximum potential benefit of this treatment?'

Bias: Tends to overestimate treatment efficacy due to selection bias, as compliant patients may differ from non-compliant ones (e.g., healthier, more motivated).

PP Analysis - Efficacy vs. Bias

Per-protocol (PP) analysis evaluates outcomes only for participants who strictly adhered to the trial's protocol. This creates a trade-off between measuring a treatment's ideal effect and introducing bias. It answers the question: "Does the treatment work under ideal conditions?"

Pros	Cons
Best estimate of efficacy	Breaks randomization
Measures true biological effect of a treatment if taken as prescribed.	Introduces selection bias & attrition bias.
	Groups may no longer be comparable, leading to confounding.
	Generally overestimates the treatment effect.
	Not reflective of real-world effectiveness.

PP vs. ITT - Ideal World vs. Real World

📌 Mnemonic: ITT = In The Real world; PP = Perfect Patients.

This table contrasts the two main approaches for analyzing data in Randomized Controlled Trials (RCTs).

Feature	Per-Protocol (PP) Analysis	Intention-to-Treat (ITT) Analysis
Question Answered	Efficacy: Does the treatment work under ideal conditions?	Effectiveness: How well does the treatment work in the real world?
Patient Group	Includes only patients who strictly adhered to the protocol.	Includes all randomized patients, regardless of adherence or withdrawal.
Preserves Randomization?	No, can break randomization.	Yes, preserves the original randomization balance.
Primary Bias	Attrition bias; non-adherent patients may differ systematically.	Conservative; may underestimate true effect (bias towards the null).
Interpretation	Measures treatment efficacy (Explanatory trials).	Measures treatment effectiveness (Pragmatic trials).

High‑Yield Points - ⚡ Biggest Takeaways

Per-protocol analysis only includes participants who strictly adhered to the clinical trial protocol.

It estimates a treatment's true efficacy under ideal conditions, not real-world effectiveness.

This approach is highly susceptible to selection bias, as reasons for non-adherence are often not random.

It frequently overestimates the treatment effect compared to an intention-to-treat (ITT) analysis.

Excluding non-adherent patients disrupts the initial randomization, compromising the study's validity.

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