This report is an exploration of objectively measured and self-reported physical activity and sedentary levels in Scottish 10-11 year old participants in the longitudinal Growing Up in Scotland ( GUS) study. We present these activity levels using two differing approaches: self-reported (questionnaire based), and objectively measured ( i.e. using activity monitors) physical activity. A key objective of this report was to explore the socio-economic and gender patterning of activity and assess whether these patterns differ by alternative physical activity measurement assessment approaches. The analyses presented within the report form part of a wider academic study exploring the environmental determinants of physical activity in young people that also incorporates GPS data on where young people are most active  .
1. What are the objectively measured physical activity and sedentary levels of Scottish 10-11 year old children?
2. What proportion of Scottish 10-11 year old children meet the current nationally recognised physical activity guidelines of accumulating at least 60 minutes of moderate to vigorous ( MVPA) per day when objectively measured?
3. Do differences in physical activity/sedentary levels and proportion of children meeting the guidelines exist by gender and area level deprivation?
4. Do gender or socio-economic patterns differ by whether self-reported or objective methods are used to assess physical activity?
The Growing Up in Scotland study
The Growing Up in Scotland ( GUS) study is a nationally representative cohort study that began in 2005 with an aim of tracking the lives of children through childhood and beyond. Fieldwork for the present report took place between May 2015 and May 2016. From an invited sample of 2,162 children, 774 (36%) provided valid data for the analysis in this report. Data was weighted to address response bias, and therefore ensure the representativeness of the sample to the wider population of 10-11 year old children living in Scotland.
Measurement of Physical activity
Physical activity was measured through two separate methods: (i) objectively through an accelerometer activity monitor (ActiGraph GT3X+), and (ii) via self-report using the Physical Activity Questionnaire for Children ( PAQ-C). Physical activity monitors were requested to
be worn on a belt around the waist for 8 consecutive days (with a minimum of five days, including one weekend day, required to be included in this report) and data from the devices were used to classify the level of children's activity throughout the day as time spent (a) Sedentary or (b) in Moderate to Vigorous Physical Activity ( MVPA). Time spent in MVPA was used to estimate the proportion of children who currently meet the UK's joint Chief Medical Officers ( CMO) recommended physical activity guidelines of at least 60 minutes of MVPA every day (the 'threshold' approach). In addition, a proportion was calculated for those who spent on average 60 minutes or more per day in MVPA (the 'averaging' approach).
The self-reported questionnaire was used to create a measure of 'general levels'  of physical activity resulting in an activity score between 1 and 5 (with 5 representing higher levels of activity).
Although the nature of the self-report measure did not allow assessment of guideline adherence that could be compared with the objective measure, both measures were compared for how they classified active versus non-active children.
Both the objective measure and the self-report measure were used to examine differences in activity level by gender and area deprivation.
Activity levels of 10-11 year olds in Scotland
- On average, children were sedentary for 7.5 hours per day (7.7 hours during weekdays and 7.1 hours on weekends) - objectively measured.
- On average, children spent 73 mins in moderate to vigorous physical activity ( MVPA) per day (76 minutes per weekday and 64 minutes per weekend day) - objectively measured.
- 11% of children achieved the current recommended levels of daily MVPA when analysed with the requirement of at least 60 minutes of MVPA every day ('threshold approach') - objectively measured.
- 60% of children achieved the current recommended levels of daily MVPA when analysed with the requirement of at least 60 minutes MVPA per day on average ('averaging approach') - objectively measured.
- On average, children scored 3.12 on the Physical Activity Questionnaire for Children ( PAQ-C) - self-reported . This is similar to data from English children which found a mean PAQ-C score of 3.10 in children aged 10-11 years old.  A number of 'cut- off' levels have been introduced with scores of 3.0 being consistently recognised as 'high activity'. On average, Scottish 10-11 year olds, as measured by the PAQ-C thus demonstrate high activity levels.
Differences by Gender
- No statistically significant differences in objectively measured sedentary behaviour were found by gender (7.6 hours vs. 7.4 hours, girls and boys respectively) - objectively measured.
- Yet boys spent significantly more time in objectively measured MVPA than girls (78 minutes vs. 68 minutes) - objectively measured.
- No statistically significant gender differences were found in the 'threshold' approach to guideline adherence (12% boys and 11% girls); however, a significantly higher proportion of boys met the guidelines than girls when using the 'averaging' method (69% vs. 52%) - objectively measured.
- Boys scored significantly higher on the PAQ-C than girls (3.19 vs. 3.05)  - self- reported.
Differences by level of Deprivation
- No statistically significant differences in sedentary time were found across quintiles of the Scottish Index of Multiple Deprivation ( SIMD) - objectively measured.
- No statistically significant differences in MVPA were found by SIMD quintile - objectively measured.
- No statistically significant differences in PAQ-C scores were found by SIMD quintile - self-reported.
- It is of interest to note that when these children were aged 6, mothers' reports of physical activity also did not differ greatly by area deprivation.
Difference in gender and socioeconomic patterning by method of assessment
- Both objective and self-reported methods identified gender differences in physical activity ( MVPA and PAQ-C score).
- Both objective and self-reported methods identified little patterning by either MVPA or PAQ-C score by SIMD quintiles.
Discussion and conclusions
Discussion and debate exists within the field of physical activity measurement regarding the differences between what is objectively known ( e.g. accelerometry) and what is self- reported ( e.g. questionnaire), with self-reported methods often considered as an inferior set of measurement approaches. Our report illustrates that both methods of measuring physical activity are able to identify gender differences in this age group, whilst also demonstrating similar socioeconomic patterns. Depending on the reason for conducting large scale population surveillance studies ( e.g. to track the potential social inequalities in physical activity across time using SIMD quintiles), there is an argument, if the data supports the intended outcomes, to use self-reported physical activity levels from the PAQ-C. This has a number of logistical and financial benefits including ease of administration (and potentially low participant burden) and lower set up and operating costs.
Our report highlights a continuation of a long standing issue within the physical activity literature, namely the discrepancy between the objectively measured proportion of children who meet the current physical activity guidelines (and their multiple methods of analytical approach), and that which is derived from self/proxy-reported measurement. Our results suggest that either 11% or 60% of 10-11 year old Scottish children meet the current recommended daily guidelines of physical activity. Additionally, depending on the approach used, boys are more likely to meet the guidelines than girls at this age. These figures are lower than that reported at a national level ( e.g. the Scottish Health Survey and Health Behaviour in School-aged Children survey), and further research should investigate the discrepancy between methods.
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