The increased risk of having a car crash attributed to people using their cellphones while driving may have been overestimated in some past studies, a US analysis said.
So-called “distracted driving” has become a big public health issue in recent years, and the majority of US states now ban texting behind the wheel.
But studies have reached different conclusions about how much of an added crash risk there is, and a recent analysis by researchers at the Wayne State University School of Medicine in Detroit found that two influential studies may have overestimated the risk.
Lead author Richard Young wrote in the journal Epidemiology that the method of two studies on the issue –1997 study in Canada, and another from Australia in 2005, which said that cellphone use while driving raised the crash risk four-fold – may have posed problems.
The studies recruited people who had been in a crash, and then used their billing records to compare their cellphone use during the time of the crash with their cell use during the same time period the week before, a so-called “control window.”
“Earlier studies likely overestimated the relative risk for cellphone conversations while driving by implicitly assuming that driving during a control window was full-time when it may have been only part-time,” he wrote.
Such “part-time” driving would necessarily cut the odds of having a crash, and possibly reduce people's cellphone use, during the control window – and make it seem as if cellphone use is a bigger crash risk.
The two studies asked people if they had been driving during the control window, but they did not account for part-time driving.
Young and his team used GPS data to track day-to-day driving consistency for 439 drivers over 100 days.
The days were grouped into pairs: day one was akin to the “control” days used in the earlier studies, and day two the equivalent of the “crash” day.
Overall, there was little consistency between the two days when it came to driving time. When he looked at all control windows where a person did some driving, the total amount of time on the road was about one-fourth of what it was during a “crash” day.
If that information were applied to the two earlier studies, Young estimates, the crash risk tied to cellphone use would have been statistically insignificant -- and may help explain why some earlier studies have not linked cellphone use to an increased crash risk.
Fernando Wilson, an assistant professor at the University of North Texas Health Science Center who was not involved in the analysis, said that the two earlier studies may well have overstated the risk.
But a number of other studies designed in different ways suggest that cellphone use – and especially texting – is indeed hazardous on the road, he added.
In his own study published last year, Wilson looked at information from a government database tracking deaths on US public roads.
After declining between 1999 and 2005, deaths blamed on distracted driving rose 28 percent between 2005 and 2008.
“In wider policy, I don't think this study is going to change the conversation about distracted driving.