A city planner claims that a traffic light at a particular intersection was necessary, and installing it decreased the wait time for right turns.

At each of the hours during a 24 hour period, she records the wait time in seconds before and after the traffic light was installed.

1. Construct the appropriate null and alternative hypotheses by hand.

2. Use Excel to enter “time headings” in cell a1, “seconds before” in cell b1, “seconds after” in cell c1, “difference: before - after” in cell d1, and “increase/decrease” in cell e1.

3. Starting with cell a2, enter the times of day (12 am, and so on) consecutively.  

4. Starting with cell b2, enter the wait in seconds (10, and so on) before the traffic light.

5. Starting with cell c2, enter the wait in seconds (23, and so on) after the traffic light.

6. Starting with cell d2, enter the difference in seconds, after - before (13, and so on).  To do this, construct a formula for after – before, recalling that = should precede all excel formulas.

7. Starting with cell e2, enter whether there is an increase or decrease (increase, and so on).

8. Use data >> data analysis >> t-test: paired differences for two means.  Place this information in cell g2.  (If the data analysis package needs to be loaded, then file>>options>>add-ins>>go>>analysis toolpak)

9. List the test statistic TS=t=______________.

10. List the critical value CV=______________.

11. List the appropriate P-value = ___________.

12. Determine whether to support or reject the claim at the   significance level.

13. If some commuters stated that their wait time has increased, what information would be relevant to ask them?

                Time Before              Time After 

12 am             10                                23                   

1 am               9                                  22

2 am               8                                  21

3 am               10                                27

4 am               15                                24

5 am               19                                28

6 am               23                                27

7 am               67                                38

8 am               56                                37

9 am               42                                34

10 am             34                                23

11 am             39                                27

12 pm             48                                31

1 pm               45                                29

2 pm               32                                28

3 pm               23                                21

4 pm               60                                47

5 pm               78                                42

6 pm               51                                39

7 pm               49                                23

8 pm               26                                22

9 pm               17                                23

10 pm             9                                  22

11 pm             8                                  21