Sample Size Calculator for MD Thesis & Clinical Research

Sample Size Calculator

Determine the optimal number of participants for your research study.

Enter Study Parameters

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Confidence Level (%) Usually 95%. Use 99% for high precision.

Power (%) Usually 80%. The ability to find a difference if it exists.

Expected Dropout Rate (%) Safety margin for lost participants (10-20%).

Required Sample Size: 0 Total Participants

Why Sample Size Matters?

Calculating the correct sample size is the most critical step in research methodology. If your sample is too small, you may miss a significant finding (Type II Error). If it is too large, you waste resources and time.

Choosing the Right Formula

This calculator automatically selects the correct formula based on your study design:

Study Design	Typical Formula Used	Key Input Required
Descriptive / Prevalence	Cochran's Formula (n = Z2pq / d2)	Prevalence (p), Precision (d)
Descriptive / Mean	Estimation of Mean (n = Z2σ2 / d2)	Standard Deviation (σ), Precision (d)
RCT / Case Control	Difference of Proportions	P1 (Control), P2 (Intervention), Power

Common Terms Explained

• Confidence Level (1-α): Usually set at 95%. It means you are 95% confident that the true population value lies within your interval.
• Power (1-β): Usually set at 80%. It is the probability of correctly rejecting the null hypothesis when it is false.
• Precision (d): Also called the margin of error. For prevalence studies, this is often set at 5% (0.05).

Application in Medical Research

Whether you are conducting a cross-sectional survey on diabetes prevalence or a randomized controlled trial (RCT) for a new drug, accurate sample size estimation ensures your study is scientifically valid and ethically sound.