1
A two-group experiment plans 128 analyzed participants based on the primary outcome, then recruits 150 to allow for attrition.
8 Sample Size Examples
Use these examples to study structure, specificity, tone, and variation. They are demonstrations—not claims about a real person or organization unless the example itself makes that explicit.
Before you copy
What to notice in the examples
A justified sample size follows from the study design and inferential goal, accounts for expected variability or information needs, anticipates attrition or unusable data, and distinguishes planned from achieved sample size.
- Unit of analysis and primary outcome or analytic purpose.
- Quantitative power/precision or qualitative information rationale.
- Design effects, subgroup needs, attrition, or nonresponse allowance.
- Planned, recruited, excluded, and analyzed counts.
2
A prevalence survey chooses a sample for a target margin of error and inflates it for expected nonresponse.
3
A cluster trial increases the individual-level estimate to account for correlation within sites.
4
A qualitative interview study begins with a planned range of 20–30 diverse participants and reviews whether new interviews continue to add relevant categories.
5
A document analysis includes every eligible annual report because the population is small enough for a census.
6
A usability study runs repeated small rounds because the goal is detecting interface problems, not estimating population prevalence.
7
A subgroup analysis requires sufficient participants in each age band, so the total sample is determined by the smallest planned subgroup.
8
A longitudinal study reports 420 enrolled, 366 retained, and 351 included in the final model after prespecified missing-data rules.
Keep the underlying decision or pattern, then replace the subject, evidence, relationship, constraints, and tone with details that belong to your situation. If your final line still works after swapping only one noun, it may be too close to the example.