Interpreting Commercial Vehicle Survey Data

Abstract

Analytical rigour in statistical analysis is often taken for granted. Although every effort may be made in the initial phases, there may be several factors which influence the resulting accuracy of data. This paper describes some fundamental post-survey statistical analyses, with particular reference to commercial vehicle surveys. The greater Sydney region Commercial Vehicle Survey is used to illustrate how data can be misinterpreted if errors are not quoted or calculated properly. Stratification of samples, response rates, means, medians, data distribution and sampling errors using the relative standard error, are all discussed with emphasis on the role and calculation of each, and how easily the data and statistics can be misinterpreted.