These calculations are quite complicated and rely on various assumptions. Use of mean lengths is not as useful as length distributions and is not used widely. Because of its limited use, we do not expect the absence of the PSE to cause any problems or lead to incorrect conclusions about a fishery. The PSE, or proportional standard error, expresses the standard error of an estimate as a percentage of the estimate and is a measure of precision. Precision refers to the dispersion of sample measurements used to calculate an estimate and the resulting variability in the estimate.
Large PSEs indicate high variability around estimates and therefore low precision.
It is desirable to have small PSE's and more precise estimates. There is a direct relationship between precision and sample size. When we group year, state, wave, or mode estimates, sample size increases and so does precision. Catch estimates for commonly caught species that show up in the marine recreational fishery often are more precise than for rare event or pulse fisheries. Data users should consider the width of confidence intervals surrounding estimates before drawing any far-reaching conclusions from point estimates.