What should I consider when deciding on sample size?

The Wise son:

This is definitely an important issue for research since it forces you to think about your study design. I call the sample size consideration a sanity check of the study plan. Good planning will result in an efficient study and will protect from scientific pitfalls. Example of issues you are likely to encounter; What are you testing? proportions, survival group comparison or demonstrating some dose-response association. Will there be repetitions in the study or follow-up over time? What are the key co-factors to consider? What is the sampling scheme? Any possible biases to avoid? And are there sub-groups analyses? I usually follow this paper (and the Hebrew link is here).

The Simple son:

Stop asking so many questions, Wise. It is just about plugging parameters into a formula. The main parameters are statistical significance (α), statistical power (1-β), clinical effect size, and degree of the outcome dispersion (σ²). There are plenty of sample size calculators on the web to help you with that.
KISS - keep it simple and short.

The Wicked son:

Sorry to ruin the party guys, but you are aware of the budget limits, right? You can calculate all you want till tomorrow, but who can afford the perfect study? Well, let me tell you. No one. And when you start trying to fit in the budget limits, you need to give up being wise and start being smart. Take it easy guys.

The Simple son:

Hey Wicked, I thought you were about to warn us against large sample size and how it leads to finding statistically significant effect but with no clinical importance…

The Wicked son:

Oh, don’t get me started! When researchers get into a gold mine, which is nowadays called “big data”, they think they can find any effect size they want because it all comes out significant! Be careful with that guys, you may end up finding that the number of grandmas has a statistically significant effect on the amount of money spent on chocolate.

He who couldn’t ask:

Oh man, and I thought this would be easy… I once tried those web calculators and got nowhere. Then you started with those Greek letters and I’ve lost you. I have here a medium-size apple pie with a small-size vanilla ice-cream ball, and I’m willing to share it with N study participants due to my big-sized heart.

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Tal has over 5 years of experience of consulting researchers on a variety of biomedical research including cardiology, internal medicine and infectious disease.  As a biostatistician, she is engaged in study life cycle from planning throughout the statistical analysis and up to publication.  She also took part in big-data analysis as part of evaluating Hospital databases.  Tal has served as a clinical trials’ statistician for number of studies.  She is an R programmer and has been teaching short courses of applied biostatistics with R in Tel-Aviv university and Ono Academic College.

Dina has a strong background in statistics and a high level of data analytics abilities.  She has over 5 years of experience in applied biostatistics.  Dina holds an M.A. in Biostatistics and a B.A in statistics both from the Hebrew University.

Ronit manages all of IntegiStat's administrative affairs. She has experience in office management in general and specifically in the health sciences, and is certified in accounting and law.

Diklah founded and heads IntegriStat. She has extensive experience in managing diverse data projects of all sizes. Diklah has extensive experience in providing support to companies running clinical trials to validate their product for regulatory clearance including FDA and EMA.

Her professional experience also includes: statistician at West Pennsylvania Psychiatric Institute; establishment of a statistical service at Wolfson Medical Center, Holon; lead biostatistician at a number of biotech startups.

Diklah is the author or coauthor of more than 50 scientific publications. Diklah has a B.Sc. in Statistics from University of Haifa; an M.Sc. in Biostatistics from the Graduate School of Public Health, University of Pittsburgh; a Master of Entrepreneurship and Innovation degree from ISEMI, Swinburne University of Technology; and Ph.D. in Biostatistics from Ben Gurion University of the Negev.