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In theory, the reflexes and eyesight of elderly Americans affect their ability to drive safely. The same should hold true for the effects of cognitive decline. New data show that tests given to older people to ascertain their ability to drive safety may be worthless.

The Insurance Institute for Highway Safety (IIHS) and the Highway Loss Data Institute (HLDI) collected data from two states that give driving tests to old people. The results were decidedly mixed. In Illinois, road tests of people 75 and over seem to have cut accidents. In New Hampshire, the tests were ineffective.

Why put the tests in place at all? According to the HLDI:

Per mile traveled, older drivers crash more often than middle-age adults, though not as often as young drivers.

Tests in Illinois are meant to push older drivers off the road via changes in the driver license test cycle:

Illinois is the only state that currently has a road-test requirement for older drivers. The requirement applies to all drivers age 75 and older. All Illinois drivers 80 and younger must renew their licenses every four years. Drivers 81-86 must renew every two years, while those 87 and older are required to renew annually.

The state’s requirements have resulted in fewer older people driving than otherwise would be expected, HLDI’s analysis shows. Those older drivers who do remain on the roads are somewhat less risky than older drivers in nearby states.

New Hampshire data point to a different conclusion:

New Hampshire didn’t see the same benefit from its road-test requirement, which was in effect for drivers age 75 and older until 2011. Renewal is required every five years for all drivers, regardless of age.

The 2011 test law was taken off the books in 2011.

The study looked at crash levels in adjacent states and insurance claim rates. In Illinois, the states were Indiana, Iowa, Missouri and Wisconsin. In New Hampshire they were Vermont and Maine. The study results were considered imperfect for several reasons, including that there is more public transportation in Illinois than in New Hampshire.

The lack of consensus about the rate of tests of older drivers means that it will be harder for states to adopt laws that increase driver test frequency for the elderly. They also will bolster the claims of old people who say that they should not be discriminated against when many of them have had practice driving for decades.