The table below summarizes information gathered about drivers on I-95 in Marylan

Question

The table below summarizes information gathered about drivers on I-95 in Maryland in a study discussed by John Lamberth. a journalist for the Washington Post. This data pertains to drivers in general and not necessarily those who were stopped. In addition, it was noted that 35% of those actually stopped for speeding violations were African American. Assume for the sake of this exercise that someone is pulled over only if they are in violation of speeding. Use this information above to fill in the entries of the following table (each entry in the table below should be a probability). Since we don't know the probability of a given speeder being stopped, we will simply call this p. We place this entry in the upper right hand corner of the table below. Some of your answers to this part of the question will depend on p. You should fill in the table using the information above. What is the probability that a driver is stopped, given that the driver is speeding and African-American? What is the probability that a driver is stopped, given that the driver is speeding and not African-American? How many more times likely is a speeding African American to be pulled over compared to a speeding non-African American?

Explanation / Answer

(a)

There are a total of 5354 drivers who are speeding. there are a total of 938 drivers who are African Amrican and speeding. Thus probability of an African American driver speeding = 938/5354 = 0.175

Rest of the terms can be calculated based on this.

(b)

P(driver is stopped | driver is speeding and african american) = 0.35p/0.175 =2p

(c)

P(driver is stopped | driver is speeding and not african american) =0.65p/0.825 = 0.79p

(d)

P = 2p-0.79p = 1.21p

Speeding African American Speeding Non-African American Row totals Stopped 0.35p 0.65p p Not Stopped 0.175-0.35p 0.825-0.65p 1-p Column Totals 0.175 0.825 1

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