Fixed-sample size sampling plan

Definition

A sampling protocol in which the number of sampling units (e.g., quadrats, traps, transects, or time intervals) is predetermined and held constant across surveys, regardless of the variance or density of the target population encountered. This approach contrasts with sequential or variable-sample plans and is commonly employed when logistical constraints require standardized effort or when statistical power calculations have established a sufficient *n* for detecting a specified effect size.

Etymology

From statistical quality control and ecological sampling theory; "fixed" denotes the predetermined, non-negotiable sample size, distinguishing it from adaptive or sequential alternatives.

Example

An entomologist monitoring Colorado potato beetle (*Leptinotarsa decemlineata*) density in commercial fields uses a fixed-sample size sampling plan of 50 randomly selected potato plants per field, counted weekly, to ensure comparable precision across multiple farms and growing seasons without adjusting effort based on preliminary counts.

Synonyms

• constant-sample size design
• fixed-*n* sampling
• predetermined-sample plan

Related Terms

• sequential sampling plan
• binomial sampling
• Precision
• sampling unit
• quadrat sampling
• transect
• Type I error
• statistical power

Usage Notes

Fixed-sample plans sacrifice potential efficiency when populations are very sparse or abundant (where fewer or more samples might suffice, respectively) but provide unbiased variance estimates and straightforward comparability across studies. In entomology, they are standard for long-term monitoring programs, resistance documentation, and regulatory surveys where methodological consistency outweighs cost optimization. The term is often hyphenated as "fixed-sample-size" when used attributively.