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November 23, 2014

November 23, 2014

Posted by **G.** on Thursday, June 19, 2008 at 5:14am.

Accident rate for Dallas Fire Trucks

Statistic Red Trucks Yellow Trucks

# of Accidentsx1=20accidents x2=4accid

# of fire runsn1=153,348 n2=135,035

- statistics -
**MathGuru**, Saturday, June 21, 2008 at 8:44pmHypotheses:

Ho: pY = pR (R = red trucks; Y = yellow trucks)

Ha: pY < pR

You can use a binomial proportion 2-sample z-test for this kind of problem.

Here is one formula for this type of test:

z = (pY - pR)/√(pq(1/n1 + 1/n2)

p = (x1 + x2)/(n1 + n2)

q = 1 - p

pY = 4/135035

pR = 20/153348

p = (4 + 20)/(135035 + 153348)

q = 1 - p

Convert to decimals and substitute into the formula. Calculate z. Compare to the cutoff z at .01 for a one-tailed test (Ha shows a specific direction, so the test is one-tailed). Determine the p-value, which is the actual level of the test statistic. Determine whether to reject Ho (the null hypothesis) or fail to reject Ho. If you reject Ho, then you accept Ha and the test is statistically significant.

I hope this will help get you started.

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