You run a pet-grooming business, Paws For Effect. Over the last few years, you have steadily built your business. The data set paws.xls contains sales data for the last 30 + 1 = 31 months. In the most recent month a competitor business, Furrtasic Felines, has set up nearby. Your task is to develop a linear model that can predict revenue based on month for the first 30 months' data. Subsequently, you want to evaluate if the revenue for month 31 is significantly lower than might be expected from natural variation.

Calculate your linear regression based on the data from months 1 to 30, i.e. do not include month 31 in the regression. Month Revenue 15 22 14 27 18 L OO V O UT A W N H 19 23 21 29 10 29 11 25 12 25 13 30 14 31 15 33 16 30 17 41 18 36 19 32 20 38 21 36 22 36 23 43 24 32 25 34 26 40 27 42 28 34 29 35 30 44 31 30