Sampling Error
Definition
The difference between a sample statistic and the true population value, arising from the randomness of selection. It can be estimated from the sample itself, decreases with larger samples, and is quantified through standard errors and confidence intervals.
- Cause
- Randomness of selection, not systematic skew
- Behaviour vs sample size
- Decreases as sample size increases
- Quantifiable?
- Yes, from the sample itself
- Measured via
- Standard errors, confidence intervals
Common questions
Why is sampling error considered a normal and expected part of any sampled estimate?+
Any time a subset rather than the full population is measured, chance variation in which units happened to be drawn will make the sample statistic differ somewhat from the true value, and this is expected even when selection is perfectly random.
How does an analyst reduce sampling error in a forensic dataset?+
Increasing the sample size is the standard lever, since the standard error typically shrinks with the square root of sample size, tightening the confidence interval around the estimate without needing to change how units are selected.
Why is it important to distinguish sampling error from sampling bias in a report?+
Reporting a confidence interval only addresses random sampling error; if the underlying selection process was also biased, the true value can still fall well outside that interval, so conflating the two overstates how precise the estimate really is.
Related terms
- Cluster Sampling
- A design in which the population is divided into naturally occurring groups called clusters, a random sample of clusters is selected, and...
- Sampling Bias
- A systematic distortion in an estimate caused by a selection process that does not give all units a known probability of inclusion....
- Sampling Frame
- The list or description of all units from which the sample can be drawn. Any unit not on the frame cannot be...
- Simple Random Sampling
- A design in which every possible subset of a given size has an equal probability of being selected. It requires a complete...
- Stratified Sampling
- A sampling design that divides the population into homogeneous subgroups (strata) and samples each stratum separately. Allows the auditor to apply higher...