A major concern associated with these procedures is the accuracy and precision of the survey results. Accuracy refers to the magnitude of systematic errors or degree of bias associated with an estimation procedure. This affects how well the estimated value represents the true value. Systematic errors may or may not be measurable and can cause estimates to consistently under or over-estimate the true value. In contrast, precision refers to the variability in estimates.
High precision means that random variation associated with the collection procedure is minimized.
Generally larger numbers of samples provide greater precision than small numbers. Acceptable levels of accuracy and precision should be determined prior to conducting a survey. Confidence limits are a derivative of these standard measures of variability. They delineate an upper and lower limit around an estimate and provide a probability that the true value is contained within this range. As variability increases, it widens the confidence intervals at a given probability and erodes the confidence with which population parameters may be estimated.