An F-test checks if any additional predictor xj helps to improve the part of variance to be explained probabilistically. The final aim
is to reduce the number of independent variables xj to a minimum
and to use these to explain a maximum part of variance. For the
present study the defined explanatory independent variables and the corresponding values are shown in Table 1. The sample size varies from 58 to 62 educational buildings, because the buildings were only used if all analyzed characteristics were known.