The elegant study, designed by the Public Service Research Institute in Maryland, had taken photos with high-speed camera equipment and a radar gun of nearly 40,000 drivers on the turnpike. The researchers then showed the photos to a team of three evaluators, who identified the race of the driver. The evaluators had no idea if the drivers in the photos had been speeding. The photos were then correlated with speeds.
The driver identifications are not reliable! whined the Justice Department. The researchers had established a driver?s race by agreement among two of the three evaluators. So in response to DOJ?s complaint, the researchers reran their analysis, using only photos about which the evaluators had reached unanimous agreement. The speeding ratios came out identically to before.
The data are incomplete! shouted the Justice Department next. About one third of the photos had been unreadable, because of windshield glare that interfered with the camera, or the driver?s position. Aha! said the federal attorneys. Those unused photos would change your results! But that is a strained argument. The only way that the 12,000 or so unreadable photos would change the study?s results would be if windshield glare or a seating position that obstructed the camera disproportionately affected one racial group. Clearly, they do not.