Information by Design
Lifestyle Survey Toolkit

Precision and Bias

Increasing precision and reducing bias are the two primary objectives in conducting a reliable survey:
  • Precision is about how precise or accurate your results are; how narrow the confidence intervals are for estimates from your survey
  • Bias is about whether your survey really is representative of the population of residents.

For example, a survey might give an estimate of smoking prevalence in the adult population in an area as 15%. With 1,000 respondents this could be accurate to within +/- 3% (a precise estimate!). But, if the sample excludes younger adults, the estimate of smoking prevalence will be biased (even if it is accurate!).

This is an extreme case but more commonly seen where some sub-groups of the population have lower response rates than others.

For an excellent easy-to-read summary of sampling errors, precision, bias and confidence intervals, see Hoinville et al pages 56-60.

Further information on Non-response Bias, including research on it's effects is available by clicking here.