Three different sections of the same Interstate highway, with almost equal traffic volumes, have been patrolled by the State Police at different levels of intensity for the past six months. The posted speed limit is 55 and the speeds of random samples of motorists have been registered for each of the three sections. Are the differences in the average speed among the three highway sections (statistically) significant? Was more intensive patrolling effective? Use the SPSS output below.

One way

1. State the null hypothesis (in words)

2. State the research hypothesis (in words)

3. Find F critical

4. Calculate Fobtained using the intermediate results from ANOVA Table. (Hint: SPSS uses the same formula for calculation of F obtained as you have in the book).

5. Make Decision, Interpret Result (Step 5) and answer the problem questions.

Speed Lightly Patrolled Moderately Patrolled Heavilly Patrolled Total Speed Between Groups Within Groups Total N 8 8 8 24 Sum of Squares 158.333 557.000 715.333 Mean 60.50 56.75 54.25 57.17 ANOVA df Std. Deviation 8.018 1.832 3.454 5.577 2 Descriptives 21 23 Std. Error 2.835 .648 1.221 1.138 Mean Square 95% Confidence interval for Mean Lower Bound 53.80 F 55.22 51.36 54.81 Upper Bound 67.20 58.28 57.14 59.52 Sig. .072 Minimum 48 54 50 48 Maximum 72 59 60 72