In order to evaluate the effect of advertising on television, e.g. how long the inhabitants of a municipality watched television during a week. The municipality consists of three villages, Norrbyn, Centrum and Sydbyn. The survey used a stratified sample with results as shown in the table below.

Antal personer Urvalsstorlek Urvalsmedelvarde Urvalsvarians NK nk y k Norrbyn 155 20 16,2 34,2 Centrum 62 8 12,6 25,1 Sydbyn 93 12 9,1 19,0