Traffic count project Name:

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x: cars/5 min
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The back-to-back holidays on Wednesday and Friday provide a week off from statistics. During this week long break the statistics class will engage in a traffic measurement exercise. During the next week find a stretch of road near wherever you happen to be.

Note the date, time, location, and name of the road - if any. For twenty-five minutes count the number of cars that pass during five minute intervals. The easiest way to do this is to simply write down the time (just the minutes will work) at which the car passes.

After twenty-five minutes, divide the data into bins of five minutes in duration each. Count the number of cars in each five minute bin and use that in your table.

Use the sample size n, sample mean x and the sample standard deviation sx to calculate a 95% confidence interval for the population mean number of cars per five minute periods using the student's t-distribution.

No two class members should use the exact same data. If you choose to do the same section of road, do it on a different day or a different time than other classmates.

Remember: If your 95% confidence interval for your mean includes nine, then your segment of road is NOT statistically significantly more or less busy than the one measured in test two out at Song Mahs in Pehleng, Kitti. If your interval is wholly and completely above nine, then your road is busier. If your interval is wholly and completely less than nine, then your road is less busy.

  1. Date: _______________
  2. Time: _______________
  3. Location: _______________
  4. Road: _______________
  5. sample size: n = ______________
  6. x = ______________ Calculate the sample mean x number of cars per five minute period.
  7. sx = ______________ Calculate the sample standard deviation sx number of cars per five minute period.
  8. confidence level: c = ______________
  9. degrees of freedom: = ______________
  10. t-critical: tc = ______________
  11. Error tolerance E: = ______________
  12. Calculate the 95% confidence interval for the population mean number of cars per five minute period:

    P( ___________ ≤ ≤ ___________ ) = 0.95
  13. _________ Does the 95% confidence interval for the population mean include nine cars in five minutes?
  14. _________ Is the result for your segment of road statistically significantly different from the Song Mahs, Pehleng, Kitti, from 17:08 to 18:08 on the 30th of October 2006?
  15. _________ Is your segment of road statistically significantly carrying more traffic, less traffic, or the a statistically same level of traffic (if your interval overlaps nine, then, statistically speaking, the two roads segments are "not distinguishable" from each other)?
  16. Why do you think you had to measure at least five intervals?
  17. Sketch the confidence interval on a number line. Include also the value of nine at Song Mahs.
Statistic or Parameter Symbol Equations Excel
Chapter nine: Confidence interval statistics
Degrees of freedom df = n-1 =COUNT(data)-1
Find a tc value from a confidence level c and sample size n tc   =TINV(1-c;n-1)
Calculate an error tolerance E of a mean for any n ≥ 5 using sx. E error tolerance =tc*sx/SQRT(n)
Calculate a confidence interval for a population mean from the sample mean x and error tolerance E:   x-E ≤ ≤ x+E