Year-on-year differences between income before tax estimates have been tested for statistical significance at a 95 per cent confidence level. An increase or decrease in estimates that is statistically significant is likely to be a genuine change, rather than resulting from chance, and means that users can have greater confidence that any apparent differences are applicable to the entire population in question.
Statistical significance in this report relates only to the fact of an increase or decrease in average income before tax and does not consider the size of the change; in some cases, apparently large changes may not be statistically significant and vice versa.
Average gross earnings, total expenses and median income before tax figures have not been tested, as standard errors were not available. Throughout the rest of the report, results and comparisons have not been tested for statistical significance unless otherwise stated.
Standard errors to support the statistical significance of the income before tax results are available in the CSV files which supplement this report. In the accompanying interactive report, margins of error, which are calculated from the standard errors, are presented. The margin of error shows the maximum expected difference between the true average income before tax and the estimate presented, with a confidence level of 95 per cent.