Over the past 20 years or so, the risk for US men and women of suffering from cognitive impairment and dementia has increased. This is the conclusion of a new study by researchers at the Max Planck Institute for Demographic Research (MPIDR) and colleagues that takes into account learning effects when repeating the same dementia test.

The burden might be heavier than long assumed: For years, most studies using survey data suggested that the risk of suffering from cognitive impairment is declining in high-income countries. They often use longitudinal surveys in which the same individuals take the same test over and over. This results in learning, which if not taken into account, may bias results.

That is why Mikko Myrskylä, Joanna Hale, Jutta Gampe, Neil Mehta and Daniel Schneider analyzed the prevalence in cognitive impairment in the United States from 1996 to 2014 taking into account testing experience and selective mortality.

“Results based on models that do not control for test experience suggest that risk of cognitive impairment and dementia decreases over the study period. However, when we controlled for testing experience in our model the trend reverses,” says Mikko Myrskylä, Director at the Max Planck Institute for Demographic Research (MPIDR) in Rostock, Germany.

In their models, the prevalence of any cognitive impairment increases for both women and men. The increase was particularly strong among Latinas, the least educated, and people over 85. Some of the increase may be driven by people living longer with dementia.

For their study, recently published in the journal Epidemiology, the researchers used data from more than 32,000 participants from the Health and Retirement Study (HRS). That is a nationally representative, biennial panel survey of US residents age 50 and older and their spouses. Among other things, it contains a version of the Telephone Interview for Cognitive Status (TICS-M), specifically modified to detect decline of cognitive abilities.

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