Question

The British Department of Transportation studied to see if people avoid driving on Friday the 13th. They did a traffic count on a Friday and then again on a Friday the 13th at the same two locations ("Friday the 13th," 2013). The data for each location on the two different dates is in table #9.2.6. Estimate the mean difference in traffic count between the 6th and the 13th using a 90% level. Table #9.2.6: Traffic Count Dates 6th 13th 1990, July 139246 138548 1990, July 134012 132908 1991, September 137055 136018 1991, September 133732 131843 1991, December 123552 121641 1991, December 121139 118723 1992, March 128293 125532 1992, March 124631 120249 1992, November 124609 122770 1992, November 117584 117263

Answer 1

1= mean traffic count on Friday the 6th = 128385.3

2 = mean traffic count on Friday the 13th = 126549.5

the sample size is n = 10. For the score differences we have

D¯=1835.8

sD^--=1176.01

level of significance= 0.10

the degrees of freedom are df= (n-1)= (10-1) = 9.

error bound of the mean of difference = 1.64*371.89 =611.70179

Confidence Interval

The 90% confidence interval is 1154.1<?d?<2517.5

We estimate with 90% confidence that the true mean difference in traffic counts between Friday the 6th and Friday the 13th is between 1154.1 and 2517.5.