**Question:** Most important factor which decides the results of a randomized controlled trial is: March 2005

A. Sample Size
B. Randomization Technique
C. Blinding Method
D. Follow-up Rate

**Core Concept:**
A randomized controlled trial (RCT) is a study design where participants are randomly assigned to receive either the experimental treatment or a control treatment. The results of an RCT are influenced by several factors, one of the most crucial being the quality of the study design. The question focuses on the initial phase of the trial, which is the selection of participants and the factors that determine the validity of the trial.

**Why the Correct Answer is Right:**
The correct answer, **D. Follow-up Rate**, is significant because it directly affects the validity of the trial's results. A high follow-up rate ensures that the data collected from participants remains unbiased and representative of the study population. Without a high follow-up rate, missing data may lead to selection bias, which could distort the results and render the trial's findings unreliable.

**Why Each Wrong Option is Incorrect:**

A. **Sample Size** (Option A) is crucial but not as essential as the correct answer. A larger sample size offers greater statistical power, but a low follow-up rate could still compromise the trial's results.

B. **Randomization Technique** (Option B) and **Blinding Method** (Option C) are important aspects of RCT design, ensuring allocation balance and reducing bias. However, they do not guarantee the accuracy of the study results if a high follow-up rate is not maintained.

**Clinical Pearl:**
A high follow-up rate in a randomized controlled trial is essential for accurate results. The trial should aim for 100% follow-up rate to minimize bias. However, it is not feasible to achieve 100% follow-up rate. Therefore, employing strategies to maximize follow-up rate, such as regular reminders, phone calls, or home visits, should be considered. Additionally, ensuring participant satisfaction, addressing harms and benefits, and providing informed consent are crucial for maintaining high follow-up rates in clinical trials.