Several of the characteristics investigated relied on child self-report and therefore may not truly reflect reality, for instance self-report screen time and recreation time, and perception of parental support may be different if they were reported by parents or teachers or observed directly.
This is a serious limitation inherent to all questionnaire-based studies (e.g. overestimation of the outcome) as for instance self-reporting of duration of computer work is inaccurate compared with objective measurements.
For instance, self-reports of both tobacco use [ 2, 22, 23] and weight status [ 24, 25] have been found to be highly related to more objective assessments of each condition and are commonly used in national surveys such as the BRFSS [ 26, 27].
Clearly, none of the methods used to measure adherence record actual intake of medication, and there are even indications that at least in some instances self-reporting is a more accurate record of adherence [ 24].
Although SBUT has some elements of subjective reporting, it is a more objective measure than, for instance, self-reported symptoms.
We will, in the first instance, use self-reports of the EuroQol EQ-5 D measure.
Some epidemiological studies use proxies for environmental chemical exposures (for instance by self-report in questionnaires) or use ecological study designs where exposure is not determined at the individual level but only by region or country, and these must be interpreted with caution.
Companies used pedometers, for instance, to get employees on their feet, but those typically required workers to self report data.
Study limitations include self report of race.
All individuals were Danes by self report.
