Sedentary behaviour assessment - case scenarios
- Screen time intervention among pre-schoolers
- School-based RCT to reduce sitting during school class-time
- Treatment program for overweight/obese primary school children
- Primary prevention of adolescent screen time in clinical settings
- Population prevalence of screen time among adolescents
Researchers plan to design and evaluate the potential efficacy of a 12-week intervention to reduce screen time in children aged 2-3 years in the home setting. Children will be randomised as a family unit to either an intervention or control group. Screen time will be assessed among approximately 80 children (40 in each group) at baseline and at 3-month post-intervention time points. The aims of this research are to (i) determine if the intervention results in reduced total screen time at home and, (ii) determine duration by each screen type.
In this scenario, the researchers are assessing changes in children’s screen time using a randomised controlled trial (RCT) design. Key outcomes of interest are the duration and context of the screen time participation at home. The sample comprises children who are too young to self-report, and the study requires details of types of screen time behaviour. Objective measurement using inclinometers or accelerometers are not appropriate as these methods will not provide the context of the behaviour or whether the sedentary time was screen time or other sedentary behaviours. An appropriate approach is a parent proxy questionnaire using recall over a certain number of days.
The number of days that represent an accurate estimate of habitual screen time behaviours in this age group and in this setting is unknown, and will depend on day-to-day variations in the home context. Ideally, weekday and weekend day screen time should be captured. However, despite recognised limitations, parent proxy self-report recall instruments can be used to provide an estimate of minutes spent in screen time and assess compliance with guidelines and determine the types of screen time in which children engage.
Traditional classroom teaching techniques predominantly involve children being seated for sustained periods. Evidence among adults suggests that sustained sitting may be detrimental to health and that interrupting sitting time may reduce such risks.32 Researchers have planned a 6-month RCT to test strategies to reduce classroom sitting in primary school children through alternative teaching practices. The RCT involves two classes within each year level at six schools (three control and three intervention schools), and approximately 300 students.
To determine the effectiveness of the intervention, researchers must detect changes in time spent ‘sitting’ during class time between baseline and post-intervention. Key considerations in the selection of appropriate measurement instruments include: the age of the participants, the need to detect behaviour within particular periods, the need to differentiate sitting from other postures, potential burden to participants and minimisation of class disruption. In this scenario, self-report measures may be inappropriate due to participant age (cognitive limitations). Proxy-reports by teachers may also be inappropriate as they would only provide group-level information rather than data about individuals. The use of self-report logs/diaries may be burdensome during class-time, may disrupt class activities and could result in reactivity. Accelerometry may also be inappropriate because they quantify ‘movement’ and do not provide any postural information. Low movement counts are indicative of limited movement and not necessarily ‘sitting’.
In this scenario, inclinometers and direct observation may be the most appropriate measurement tools. Inclinometers enable researchers to determine time spent sitting or lying (based on postural information), can be worn over long periods (e.g., one week) and allow researchers to extract data from specific periods of interest (e.g., class times). Direct observation would provide the same ‘information’ with the additional opportunity to value-add by documenting specific behaviours undertaken in each posture (e.g., reading, writing, art, craft, etc). However, direct observation may result in reactivity as participants know they are being observed, and may be costly given the number of observations that would be required (each period across the school day for each class at each school) on multiple school days. Further, the number of days of observations required is not established.
A researcher is seeking to evaluate the effects of a 10-week family-centred sedentary behaviour reduction intervention on adiposity in overweight/obese 8- to 12-year-old children. The feasibility study is a single-arm experiment involving 30 overweight/obese children with assessments of sedentary behaviour taken pre- and post-intervention, and the researcher wants to determine if the intervention reduced children’s sedentary time (i) overall daily and (ii) outside of school hours.
For this intervention, the researcher needs to selects an instrument that is both accurate and objective, and sensitive enough to detect the hypothesised changes in sedentary time. Although the sample size is relatively small, direct observation would not be feasible because it is likely that the children attend different schools, and because the researcher is also interested in understanding the effects of the intervention on sedentary time outside of school hours. Self-report questionnaires offer a cost-effective option, but the assessments would be vulnerable to recall-bias because of the age of the participants. Parent-proxy reports would also not be recommended because their estimates might be influenced by social desirability bias and this could result in under-reporting of the behaviour, or parents’ understanding of the desired effects of the intervention might result in under-reporting at post-test. It would also be difficult to accurately assess children’s total sedentary time, which occurs in many settings and contexts and not always in the presence of parents.
An objective measure is recommended and monitoring devices worn on the body, such as inclinometers or accelerometers, would be most suitable. The use of an inclinometer would allow the researcher to examine time spent in different postures, and from this changes in sitting/lying time as a result of the intervention could be evaluated. If accelerometers are chosen, the researcher can apply age-appropriate cut-points to determine sedentary time. The real-time data acquisition from objective monitoring devices would allow the researcher to specifically examine sedentary time that occurs outside of school hours, in addition to children’s overall or total sedentary time per day.
A general practitioner (GP) is concerned about the metabolic profile of an obese adolescent patient presenting markedly overweight and with obvious signs of insulin resistance. During the consultation the GP ascertains from the adolescents’ parents and the adolescent that the adolescent spends most of their time sitting on the couch playing e-games, watching TV/DVDs.
Access to adolescent obesity management clinics is limited, and because the GP has a small, busy practice is unable to provide on-going long consultations to the adolescent. The GP decides that the best management strategy will be based on regular brief counselling consultations that incorporate goal setting. The adolescent’s parents are asked to help the adolescent set realistic screen time reduction goals and to help monitor progress towards reducing screen time.
Objective measures are not suitable for several reasons. Firstly, motion sensors do not capture contextual information and, the cost of motion sensors is prohibitive to the practice budget. Furthermore, the GP does not have the time and expertise to interpret the data collected by objective instruments. Rather, the most feasible line of intervention is for the GP to ask the adolescent to complete a time use diary, or suitable structured questionnaire, about their screen time.
This baseline information will identify the duration spent on screen time and the time of day spent on screen time. The GP can use this information to help the adolescent set realistic goals aimed at reducing screen time. The GP can monitor the adolescent’s progress towards reducing screen time at on-going consultations for the monitoring the obese adolescents’ progress.
Health and education professionals have concerns about non-school recreational screen time among adolescents. In order to determine whether investments should be allocated to develop a school-based intervention to encourage adolescents to reduce their screen time, the first step is to ascertain how prevalent screen time is, and whether there are sociodemographic differences in teenagers’ screen time. To determine the population prevalence, a large sample of adolescents (i.e., several hundred) from a range of high school years, across different educational sectors, and geographical and socioeconomic areas is required to determine population estimates which are generalisable.
In this scenario, objective measures such as accelerometers and inclinometers are inappropriate for several reasons. First and foremost, objective measures do not provide contextual information, so will not discriminate between screen time activities, or other sitting behaviours, therefore self-report is the most desirable method of measurement. Unlike younger children, adolescents are capable of self-report, albeit recall can be affected by social desirability, and estimates of time are subject to large error. Questionnaires have the ability to discriminate between screen time activities and to determine habitual non-school screen time on week and weekend days. In school environments, questionnaires can be administered either as pen and paper, or via computers/smart boards.
A significant issue to consider when asking students to report screen time activities is the concept of multi-tasking. For example, an adolescent may play on their computer while watching TV – so during the administration of the questionnaire it is important to instruct respondents to allocate the time proportionally spent on each screen activity. An alternative method to measure screen time behaviour is with time use diaries/log, or ecological momentary assessment (EMA), where respondents report activities undertaken during a specified time interval. A limitation of this method is that all activities are reported, generating large volumes of data from which screen time data are extracted.
For further information see:
Hardy, L. L., Hills, A. P., Timperio, A., Cliff, D., Lubans, D., Morgan, P. J., Taylor, B. J. & Brown, H. 2012. A hitchhiker's guide to assessing sedentary behaviour among young people: Deciding what method to use. Journal of Science and Medicine in Sport. Abstract