Sample size

Definition

The number of independent observations, individuals, or replicates included in a statistical sample, chosen to achieve adequate precision and statistical power for estimating population parameters or detecting effects.

Etymology

From 'sample' (a subset of a population) and 'size' (extent or amount)

Example

In a mark–recapture study of tiger beetles (Cicindelinae), researchers calculated that a sample size of at least 200 marked individuals was needed to estimate population size with 95% confidence and a margin of error of ±10%.

Synonyms

• n
• sample number
• replicate number

Related Terms

• statistical power
• confidence interval
• effect size
• replication
• mark-recapture
• sample bias
• Type I error
• Type II error

Usage Notes

In arthropod ecology, sample size refers to the count of specimens, traps, or survey units, not the physical dimensions of a specimen. Distinct from 'sampling effort,' which combines sample size with intensity or duration. Small sample sizes are common in rare species studies and may require non-parametric methods. In morphometric studies, sample size must account for intraspecific variation and measurement error.