People who diet can expect to lose an average of 3kg in a month. In a book, the authors claim that people who follow a new diet will lose an average of more than 3kg in a month. The weight losses of the 180 people in a random sample who had followed the new diet for a month were noted. The mean was 3.3 kg and the standard deviation was 2.8kg.
(i)Test the authors claim at the 5% significance level, stating your null and alternative hypothesis.
I didnt think I had problems but the example answer given divides the standard deviation by 179 when standardizing to the normal distribution. Why not 180. Is there some other technique requiring a loss of 1 degree of freedom???
It mentions that if 180 is used then the answer will be sligtly less.