How could I justify the sample size of my research?

Hossein Ghaderi-Zefrehi @Hossein-Ghaderi-Zefrehi

25 August 2023 6 626 Report

I have performed a double-blind, placebo-controlled, randomized clinical trial with N=63 (32 in the placebo group and 31 in the intervention group). After submitting my manuscript, I received major revisions. In one of the comments, the reviewer asked me to justify the sample size. The reviewer's comment was: "Sample size justification required proper drafting"

I do not know how to justify the sample size of my research

Sample size calculation

For the calculation of sample size, the significance level and statistical power were considered as 5% and 80%, respectively. According to the study of Mesri Alamdari N and colleagues, we used 0.23 nmol/L as the change in mean (d) and 0.29 nmol/L as the standard deviation of MDA as a primary outcome. Based on the formula, we needed a minimum number of 25 participants for each group. Considering the dropout rate of 20% during the clinical trial, 30 subjects in each group will be considered.

Thanks in advance

Kind regards

Ma'Mon Abu Hammad

Justifying the sample size in your research is crucial to ensure that your study's results are reliable and applicable to the broader population or phenomenon you're investigating. The sample size determination should be based on statistical principles and the specific goals of your research. Here's a step-by-step guide on how to justify the sample size of your research:

Research Objectives and Hypotheses: Clearly state your research objectives and hypotheses. What are you trying to investigate or prove with your research?

Population Definition: Define the population that your research aims to make inferences about. This could be a specific group, a geographical area, or any other defined entity.

Level of Confidence: Determine the level of confidence (often denoted as the confidence level, e.g., 95%) you want for your results. This relates to the probability that your sample's findings accurately represent the population.

Margin of Error: Decide on an acceptable margin of error. This is the maximum amount by which you're willing for your estimate to deviate from the true population parameter.

Variability: Assess the variability of the characteristic you're measuring within the population. If the variability is high, you might need a larger sample size to achieve a certain level of precision.

Statistical Method: Choose the appropriate statistical method for your analysis. Different types of analyses (e.g., t-tests, regression, ANOVA) might have different requirements for sample size.

Calculate Sample Size: Use a sample size calculator or statistical software to calculate the sample size needed to achieve your desired confidence level, margin of error, and account for the variability in the population. There are various formulas available depending on your research design (simple random sampling, stratified sampling, etc.).

Consider Practical Constraints: Take into account any practical constraints that might affect your ability to collect and analyze data. These could include time, budget, and availability of participants.

Expected Response Rate: If your research involves surveys or questionnaires, consider the expected response rate. You might need to oversample to compensate for non-responses.

Ethical Considerations: Ensure that your sample size is large enough to respect ethical considerations, such as minimizing harm to participants and avoiding overburdening a specific group.

Comparison Groups (if applicable): If your research involves comparing different groups, ensure that each group's sample size is sufficient for meaningful comparisons.

Previous Studies: If there are similar studies in your field, consider their sample sizes and justifications. This can provide a benchmark for your own research.

Pilot Studies: If possible, conduct a pilot study to test your research methods and get an initial estimate of the required sample size. This can help refine your approach before the main study.

Justification in Research Proposal/Paper: In your research proposal or paper, provide a clear rationale for the chosen sample size. Explain how you arrived at the specific number and how it addresses the research objectives and statistical requirements.

Remember that sample size justification is not a one-size-fits-all process; it should be tailored to your specific research context. Consulting with a statistician or a mentor with expertise in your field can greatly enhance the validity of your sample size determination.

Bruce Weaver

Ma'Mon Abu Hammad, I noticed that in another thread (https://www.researchgate.net/post/MANCOVA-some_assumptions_not_met_Where_next) you stated explicitly that your response was generated by ChatGPT. Thank you for doing that. The response you posted above looks (to me, at least) like it was also generated via ChatGPT. If so, please label it as such (as you did in that other thread). Thanks for considering.

Sal Mangiafico

Hossein Ghaderi-Zefrehi , What you wrote under "sample size calculation" - Was this included in your manuscript submission ? Or what you propose adding to the manuscript after review ?

Hossein Ghaderi-Zefrehi

Sal Mangiafico ,This was included in my manuscript submission, and this should be corrected

Rainer Duesing

If this was already included in the original draft, could you please share the paragraph? Maybe the wording is unclear or ambiguous.

Sal Mangiafico

Well, honesty, I have no idea what "Sample size justification required proper drafting" means. It would nice if reviewers would actually say what they think the manuscript needs.

I think what you wrote is good. The only thing that comes to mind is that you might mention what formula or software you used.

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