Sample Size Section
STROBE asks observational-study reports to explain how the study size was arrived at, supporting transparent reporting of the reasoning behind the number of participants, cases, records, or other units studied. This is not the same as a Sampling section, which primarily explains how units were selected or recruited. Required calculations and terminology vary by design; do not invent a power analysis when none was used.
A Sample Size section explains how the study size was determined or justified and gives readers the reasoning needed to interpret that choice.
Key details
Important caveats
Scope Boundary
This is not the same as a Sampling section, which primarily explains how units were selected or recruited. Required calculations and terminology vary by design; do not invent a power analysis when none was used.
Further guidance
Content
State the target or achieved study size as appropriate and explain the design, precision, power, feasibility, convention, available population, or other rationale actually used to arrive at it.
Practical Application
State the target or achieved sample size and explain the actual basis used to determine or justify it—such as power, precision, feasibility, convention, or the available population.
Purpose
A Sample Size section explains how the study size was determined or justified and gives readers the reasoning needed to interpret that choice.
Reader Check
Can a reader tell both what the study size was and why that size was chosen, without inventing a power calculation that was never performed?
Worked Example
Example structure: “We enrolled 240 participants. The target was based on the precision required for the primary estimate and an anticipated 10% loss to follow-up.”
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): Explanation and Elaboration (opens in a new tab)PLOS Medicine / STROBE Initiative · Primary reporting-guideline evidence for observational-study setting, study size, bias, participant flow, and statistical handling including missing data and confounding.