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  • Study: Self-Reported vs Actual Levels of PA Usually Don't Match Up

    In news that may surprise exactly no one, researchers have found that people aged 50 years and older tend to overestimate the level of physical activity (PA) they accomplish—and Americans tend to be more generous with their estimations than people in other nations, or at least more so than people from England and the Netherlands.

    Those findings are part of a study, published in the BMJ Journal of Epidemiology and Community Health, aimed at better understanding the differences between subjective estimations of PA and PA data retrieved from wrist-worn accelerometers. Participants from England, the United States, and the Netherlands were recruited from 3 separate longitudinal studies that asked for self-reports on PA and had subjects wear a Genactiv wrist accelerometer 24 hours a day for 7 days. Researchers then compared the self-reported data on level and frequency of PA with the data recovered from the accelerometers. Here's what they found:

    Self-descriptions of PA levels were fairly consistent—just not very accurate, especially for Americans.
    When it came to describing themselves as "inactive," "mildly active," moderately active," "active," or "very active," all 3 groups reported similar levels of PA, with the Dutch and English slightly more inclined to avoid either extreme.

    But consistency and accuracy are 2 different things. All 3 groups tended overestimate their levels of PA when compared with accelerometer data, with the US participants registering generally larger differences. For example, only 10% of US participants reported being "inactive," while accelerometer data put that figure closer to 38%. Data from Dutch and English participants also showed a gap, though not quite as dramatic as the Americans’: 8% of participants in the Netherlands self-reported as "inactive" compared with an objective data estimate of 20%; 5% of English participants self-reported as "inactive" compared with an objective data estimate of 21%.

    “Very active” was the only activity level that didn't follow this pattern across all groups. In this category, participants tended to underestimate their activity levels, with 3% of the Dutch and English groups and 5% of the US group describing themselves as "very active" compared with objective data of 20%, 17%, and 14%, respectively.

    PA dropped off dramatically with age—and again, Americans led the way.
    Though researchers focused primarily on participants 50 and older, they did analyze self-reports and accelerometer data from ages 18 and up. They found mostly similar patterns in terms of self-reports and objective data related to levels of PA, but the differences became more stark with age, with participants 65 and older showing steep declines in PA levels. Data from the US revealed the most dramatic disparities, with 11% of participants over 65 self-reporting as "inactive," compared with objective data that put that figure at 60%.

    "It is clear that self-reports and objective measures tell vastly different stories," authors write. "Both across countries and across various socioeconomic and demographic age groups within countries, self-reports vary only moderately or not at all. At the same time accelerometry indicates large differences across certain groups."

    Researchers acknowledged the importance of self-reports, but described the goal of using such reports as a way to compare PA levels across groups as "largely elusive," regardless of whether the evaluation is a simple 5-option approach such as that used in the BMJ study, or any of a number of more complex self-report instruments.

    "The issue is not that simple self-reports of PA are less reliable than the more detailed questions for frequency of various levels of PA," authors write. "Rather the problem with both types of questions is that they are understood systematically differently by different groups…and hence are unsuitable for comparisons across these groups. For that purpose, the use of accelerometry appears indispensable."

    Research-related stories featured in PT in Motion News are intended to highlight a topic of interest only and do not constitute an endorsement by APTA. For synthesized research and evidence-based practice information, visit the association's PTNow website.