How many patients should we include in our study?
This is one of the most frequently asked questions — and one of the most critical. The answer should never be based on intuition or comparison with previous “similar” studies. Every study is unique and requires an individual sample size calculation.
In practice, many sponsors rely on shortcuts: quick literature reviews, outdated data or non-expert opinions. This often leads to incorrect sample size, which can seriously harm the study.
Too few patients → insufficient power, no statistical significance, inconclusive results.
Too many patients → unnecessarily high costs, prolonged recruitment and operational burden.
The optimal solution is a professional sample size calculation performed by experienced biostatisticians. At Biostat®, we prepare such calculations — usually within 2–3 business days.
We provide several scenario variants:
• conservative (highest statistical safety),
• baseline (recommended),
• ambitious (maximising the chance to detect effects).
Each variant comes with methodological justification and transparent input parameters.
For the calculation we need only basic information:
• expected effect size,
• number of study arms,
• expected drop-out rate,
• study design (parallel, crossover, non-inferiority, superiority),
• planned interim and final analyses,
• information on stratification if applicable.
If you don’t have all these details — we help you determine them. We can conduct a literature screening or prepare simulation scenarios to estimate key parameters and select the best direction for your scientific and budgetary goals.
The result is a reliable, transparent and data-based calculation you can use in the protocol and in grant applications (e.g., ABM, NCBR).
