Concerned about graffiti, mayors of nine suburban communities instituted a citizen community watch program. community monthly incidents after monthly incidents before burr oak 2 7 elgin corners 3 2 elm grove 6 2 greenburg 4 3 huntley 5 11 north lyman 3 9 south lyman 3 5 pin oak 5 7 victorville 2 3 click here for the excel data file (a) choose the appropriate hypotheses to see whether the number of graffiti incidents declined. assume μd is the mean difference in graffiti incidents before and after.

Just to be clear, the data are reported in the picture attached.

We set the difference in graffiti incidents between before (B) and after (A) as:
d = A - B
If the number of incidents has indeed reduced, then d will be negative.

In order to choose the hypothesis, we need to recall that the null hypothesis H₀ represents the statement that we want to prove wrong, while the alternative hypothesis H₁ represents the statement that we want to prove right.
Therefore, we want μd to be strictly negative (= 0 would mean that the number of incidents stayed constant).

Hence:
H₀ : μd  ≥ 0
H₁ : μd < 0