Self-reported data is collected by interviewing subjects about their own health status. This method of data collection requires less time and is more cost-effective than tested data, which is why it is much more readily available.
Experts in the industry have long been aware that studies relying on self-reporting will lead to some false data but this is the first time a study has been carried out to determine what types of participants are more likely to misrepresent their health.
In the study, published in PLOS ONE, researchers have revealed what study participants are most likely to give biased answers when it comes to self-reported health in order to determine when it would be preferable to use on performance tests.
IIASA World Population Program researchers Sonja Spitzer and Daniela Weber used micro-data for more than 100,000 individuals from 19 European countries from the Survey of Health, Ageing, and Retirement in Europe (SHARE) and measured how country of residence, gender, age and education influence bias.
They compared the self-reported health measures from SHARE with their tested equivalent. Participants (all over the age of 50) in SHARE were, for instance, asked if they experienced any difficulty in getting up from a chair.
Following this self-report, participants were asked to physically stand up from a chair allowing the observer to see whether there was a difference between the self-reported and 'real' mobility of the person.
A similar measure was used for cognition, where individuals were first asked to rate their memory, after which they were asked to participate in a memory test where they had to recall a list of 10 words.
Who can we trust?
Spitzer says the results revealed clear differences between participants of different ages and from different countries.
"We found large differences in reporting behaviour between countries and age groups, which indicates that one has to be careful when comparing the health of countries or age groups based on self-reported data. Southern Europeans, for instance, are more likely to overestimate their health."
In Italy, only 19.4 percent of respondents reported to have difficulty getting up from a chair, while in fact, 24.1 percent were unable to stand up when they were tested.
The reserachers argue therefore that comparing self-reported health in Southern Europe with self-reported health from other countries might lead to biased results, as Southern Europeans could appear healthier than they actually are.
According to the researchers, Southern, Central, and Eastern Europeans are much more likely to misreport their physical and cognitive abilities—both in terms of underestimating and in overestimating them—than Northern and Western Europeans.
The study further found that the older individuals are, the more likely they are to misreport their health and that a person's educational level might also play a role in how they report their perceived cognitive ability.
Weber explains: "While 85.5 percent of respondents 'get it right' in the age group 50-54, only 65.6 percent do so in the age group 90-94. This makes it difficult to compare the self-reported health of older individuals to that of younger individuals.
"Reporting behaviour also differs a lot between educational groups, especially when it comes to questions about memory. It seems like educated individuals are much more aware of their current health status than less educated individuals."
Previous literature has shown or speculated that women report their health differently from men, but this study did not find very large differences. According to the authors, this indicates that women 'cheat' as much as men do when it comes reporting on their health—at least for the mobility and cognition dimensions that were considered in the study.
In addition to the above, over- and underestimating health harms not only the reliability of survey data, but also the health of individuals themselves. Previous research showed that overrating health, for example, is also associated with riskier health behaviour—older individuals that overestimate their physical ability are, for instance, more prone to suffer fall-induced injuries.
"We want researchers and policymakers to understand that one has to be careful when relying on self-reported data, because these data are prone to reporting biases.
"We however also want to emphasise that self-reported data can still lead to valuable and informative research if the data is treated with care," Spitzer concludes.
Source: PLOS ONE
Authors: Spitzer. S. and Weber. D.
“Reporting biases in self-assessed physical and cognitive health status of older Europeans.”