Question: What is the p-value? Impact of red light cameras on car crashes. To co

Question

Question: What is the p-value?

Impact of red light cameras on car crashes. To combat red-light-running crashes -the phenomenon of a motorist entering an intersection after the traffic signal turns red and causing a crash - many states are adopting photo-red enforcement programs. In these programs, red light cameras installed at dangerous intersections photograph the license plates of vehicles that run the red light. To know how effective are photo-red enforcement programs in reducing the red-light-running crash incidents at intersections, the Virginia Department of Transportation (VDOT) conducted a comprehensive study of its newly adopted photo-red enforcement program and published the results ina report. In one portion of the study, the VDOT provided crash data both before and after installation of red light cameras at several intersections. The data (measured as the number of crashes caused by the red light running per intersection per year) for 13 intersections in Fairfax County. Virginia, are given below.

Explanation / Answer

p-value = 0.005509   (left -side alternate hypothesos for paired t -test)

t-Test: Paired Two Sample for Means before after Mean 2.513076923 1.506153846 Variance 3.905023077 2.096925641 Observations 13 13 Pearson Correlation 0.79321317 Hypothesized Mean Difference 0 df 12 t Stat 3.002280417 P(T<=t) one-tail 0.005509948 t Critical one-tail 1.782287556 P(T<=t) two-tail 0.011019895 t Critical two-tail 2.17881283

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