Results

This chapter presents the quantitative findings from the Stand Out in Class pilot study. This study was primarily designed to address issues surrounding school and participant recruitment, acceptability of the measurement tools and intervention, and school and participant attrition rates and compliance with the measurement tools to inform a future definitive trial. Although the study was not powered to provide information on a treatment effect, preliminary estimates of the effect of the intervention are reported herein to further aid the design of a definitive trial. This chapter reports on the following study objectives:

• Objective 1 – establish and refine a recruitment strategy for schools and pupils.
• Objective 2 – determine attrition in the trial (schools and children).
• Objective 3 – determine completion rates for outcome measures (and whether or not these are sufficiently high to provide accurate data in a full trial).
• Objective 4 – assess whether or not there are any differences in trial recruitment, retention and acceptability between ethnic groups.
• Objective 8 – monitor any adverse effects, such as musculoskeletal discomfort and/or disruption to the classroom/learning, to inform the design of a full trial and minimise or eliminate any such effects.
• Objective 10 – derive preliminary estimates of the effect of the intervention on children’s total daily sitting time, physical activity, indicators of health (markers of adiposity and blood pressure), cognitive function, and academic performance, engagement and behaviour.
• Objective 11 – estimate the SD of the primary outcome to inform a sample size calculation for a full RCT.

Objective 1: school and participant recruitment

A total of 24 eligible schools were approached for recruitment into this pilot study. Of these 24 schools, the study target number of eight schools consented to take part in the study, with the overall recruitment rate being 33% [95% confidence interval (CI) 0.16% to 0.55%]. Twelve out of the 24 schools did not consent to enter the study (50%) and four out of the 24 schools approached did not respond to the initial e-mail (17%). The characteristics of the participating schools are described in Table 2.

Data from the 2016–17 school census113 show that the proportion of children eligible for free school meals was similar across the recruited schools and declined schools [mean 17.1% (range 2.3–26.4%) vs. mean 17.4% (range 9.6–28.5%), respectively] for the 2016/17 academic year and across the previous 6 years [mean 31.1% (range 6.4–52.4%) vs. mean 29.6% (range 17.4–48.2%), respectively]. There was, however, a difference between the proportion of children whose first language was not English between the recruited and declined schools [mean 51.4% (range 3.9–92%) vs. mean 38.4% (range 0–93.5%), respectively], with eight of the 12 declined schools predominantly containing white British children.

Overall, the proportion of pupils at the eight schools with parental consent to participate in the trial evaluation was 75% (176/234), exceeding the target minimum sample size of 120 participants (see Chapter 2, Sample size).

Objective 2: determine attrition in the trial (schools and children)

All eight participating schools completed the trial; the overall school retention rate was therefore 100%.

At 7 months’ follow-up, the overall retention of participating children was 97% (170/176). The retention rate of children in the control group was 96% (86/90) and the retention rate of the intervention group was 98% (84/86). A CONSORT flow diagram for the study is shown in Figure 3. Two participants in the control group (2.2%) did not attend the follow-up measures because they were absent from school during the days in which these measures took place. Three participants [one control (1.1%), two intervention (2.3%)] moved away from the area during the study and hence changed schools. One participant in the control group (1.1%) withdrew their assent prior to the follow-up measures. The demographic characteristics of the participating children are shown in Table 3.

FIGURE 3 A CONSORT flow diagram for the Stand Out in Class pilot RCT. Reproduced with permission from Clemes et al.81 This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/4.0/. (Figure not reproduced here; see the original article.)

Objective 3: determine completion rates for outcome measures

Overall completion rates for the outcome measures at 7 months’ follow-up (including participants who provided valid data at both baseline and follow-up) were as follows:

• ≥ 63% for activPAL data (proposed primary outcome in a definitive trial)
• ≥ 83% for ActiGraph data
• ≥ 94% for anthropometric measures
• ≥ 69% for blood pressure
• ≥ 89% for cognitive function
• ≥ 97% for the child-reported Body Comfort Survey
• ≥ 97% for the Engagement Versus Disaffection with Learning Questionnaire
• ≥ 91% for teacher-reported Strengths and Difficulties Questionnaire data.

Objective 4: assess whether or not there are any differences in trial recruitment, retention and acceptability between ethnic groups

Table 24 in Appendix 2 displays the recruitment and retention rates for the whole sample and according to ethnic group. Ninety-eight per cent of both white British children and South Asian children provided parental consent and written assent to participate within the trial evaluation. Similarly, 98% of white British children and South Asian children completed the trial. The impact of ethnic group on acceptability of the trial overall is discussed in Chapter 5 as part of the full process evaluation, alongside discussion of objectives 5–7.

Objective 8: monitor any adverse effects, such as musculoskeletal discomfort and/or disruption to the classroom/learning, to inform the design of a full trial and minimise or eliminate any such effects

There were no serious adverse events or adverse events reported throughout the duration of the trial. Specifically, there were no reported adverse effects associated with the intervention that related to musculoskeletal discomfort and/or disruption to the classroom or to learning. Teachers’ and children’s perceptions and experiences of the intervention are discussed in detail in the process evaluation described in Chapter 5. Descriptive statistics summarising preliminary evidence of the impact of the intervention on musculoskeletal comfort, classroom behaviour, engagement with learning and markers of attainment are presented under objective 10 (objective 9, the assessment of intervention fidelity, is also covered in Chapter 5).

Objective 10: derive preliminary estimates of the effect of the intervention on children’s total daily sitting time, physical activity, indicators of health (markers of adiposity and blood pressure), cognitive function, and academic performance, engagement and behaviour

Primary outcome for a subsequent definitive trial

The proposed primary outcome for a future definitive trial is change in mean daily sitting time on weekdays (school days). Mean daily sitting time on weekdays was chosen, given that the intervention was school based. Sitting time measured across the whole school day/weekday was proposed, as this measure encompasses school hours and out-of-school hours and factors in any compensatory effects of the intervention, should any beneficial effects of the intervention experienced during school hours be cancelled out by an increase in sitting after school, for example. Table 4 displays the descriptive statistics for all activPAL variables recorded throughout waking hours on weekdays for the control and intervention groups.

A weighted linear regression model was calculated to compare the primary outcome for the subsequent definitive trial (change in average weekday sitting time between baseline and 7 months’ follow-up) between pupils in the control group and those in the intervention group. The model was weighted by the number of participants followed up in each cluster (sum of weight = 110 observations). The model was adjusted for baseline average weekday sitting time for each cluster and for average weekday wear time when awake across the two time points (baseline and 7 months). Owing to the exploratory nature of the trial, the results are presented as weighted mean differences with 95% CIs. As the variables in the regression model reflect cluster means rather than individual observations, analytically weighted least squares was the method of estimation used, in which cluster sizes were the weights.

The model revealed that children in the intervention group spent less time sitting than children in the control group. The mean difference (weighted by school size) in change in sitting time (in minutes) adjusted as described above was –30.6 minutes per day (95% CI –56.42 to –4.83 minutes per day).

The addition of baseline season of activPAL data collection to the weighted linear regression model did not affect the difference in sitting time between groups. When follow-up season was included in the model, the adjusted difference in sitting time between groups was –26.64 minutes per day (95% CI –73.08 to 19.79 minutes per day).

Sensitivity analyses of the proposed primary outcome in a definitive trial

Owing to the exploratory nature of this pilot study, participants were included in the preliminary analyses presented in Primary outcome for a subsequent definitive trial if they wore the activPAL for a minimum of 8 hours on at least 1 weekday. To assess whether or not the number of valid days of activPAL wear had an effect on the estimates (to inform wear time criteria in a definitive trial), the preliminary primary outcome analysis described in Primary outcome for a subsequent definitive trial was rerun to include only those participants with specific days of valid activPAL data. These results are presented in Table 5. Similar differences to those described in Primary outcome for a subsequent definitive trial between groups were observed for participants providing at least 2 and 3 valid days of wear; however, these differences appear to be attenuated when considering only participants with at least 4 valid days of activPAL data.

Secondary outcomes for a subsequent definitive trial

activPAL accelerometer secondary outcomes

Table 6 displays the descriptive statistics for activPAL-determined time spent sitting, standing and stepping during school class time for the control and intervention groups. The change in time spent sitting during class time was the main secondary activPAL outcome of interest. On average, control participants experienced an increase in class time sitting at 7 months’ follow-up, whereas a reduction in class time sitting was observed in the intervention group (see Table 6).

In addition, participants in the intervention group experienced an increase in standing and stepping time during class time at follow-up, whereas reductions in these behaviours were observed at follow-up in the control group (see Table 6).

Table 7 displays the descriptive statistics for activPAL-determined time spent sitting, standing and stepping measured after school for the control and intervention groups. On average, both groups experienced reductions in sitting and increases in standing and stepping after school at the 7-month follow-up, suggesting no compensatory effects of the intervention (such as increases in sitting outside of school) in the intervention group.

Table 25 in Appendix 2 summarises the descriptive statistics for all activPAL variables recorded throughout waking hours across all monitoring days, including both weekdays and weekend days. The trends observed in this table match those reported in Table 4, which summarise the mean daily activPAL variables calculated across weekdays only.

ActiGraph accelerometer secondary outcomes

Table 8 displays the descriptive statistics for all ActiGraph variables recorded throughout waking hours on weekdays for the control and intervention groups. Both groups demonstrated similar reductions in ActiGraph-determined sedentary time and small changes in light-intensity physical activity and moderate- to vigorous-intensity physical activity (MVPA) over the follow-up period.

Table 9 displays the descriptive statistics for the ActiGraph variables measured during class time and Table 10 displays the same variables measured after school. Children in the control group reduced their ActiGraph-determined sedentary time during the after-school period, whereas the intervention group children reduced their sedentary time both during class time and after school. Children in the intervention group exhibited increases in time in light-intensity physical activity and MVPA during class time and small increases in these behaviours after school, whereas participants from the control group exhibited increases in these behaviours after school only at follow-up.

Health markers (adiposity and blood pressure)

Table 11 displays the descriptive statistics for the anthropometric and blood pressure measurements taken from participants at baseline and follow-up. The changes seen in the anthropometric measurements over the follow-up period are reflective of typical growth-related changes in children of this age.

Cognitive function

Cognitive function was assessed using three separate tests: the Stroop test, the Corsi block-tapping test and the RVIP test. The outcomes derived from these measures are summarised in Table 12. Overall improvements in the performance on most test components were observed in both groups over the follow-up period, probably due to a learning effect of these tests.

Musculoskeletal comfort

Table 13 presents results from the child-reported Body Comfort Survey (summarised scales), which shows the proportion of pupils who feel good at their desks. At the 7-month follow-up, there was an increase in the proportion of pupils from both groups who reported that they felt better at their desk.

Classroom disruption and pupil behaviour

Pupil behaviour, conduct in the classroom and interactions with fellow pupils were examined using the teacher-reported Strengths and Difficulties Questionnaire. Descriptive statistics for this measure for the control and intervention groups at baseline and follow-up, along with the changes in ratings, are summarised in Table 14. The lower the score in each subscale, and the lower the total score, the better the behaviour. The intervention group generally had reduced antisocial and hyperactive behaviours and increased self-control compared with the control group at follow-up.

Engagement and disaffection with learning

Participants self-reported their engagement and disaffection with their own learning using the Engagement Versus Disaffection with Learning Questionnaire. Table 15 summarises the scores for each subscale of this measurement tool at baseline and at follow-up, along with the changes in scores calculated over the follow-up period. There were no noticeable between-group differences in the mean change in any subscale score over the trial period.

Academic progress and attainment

An overview of the results for school performance per class is shown in Appendix 2, Table 26. Table 16 shows the combined data from which the comparisons were made. There were no differences between change in expectation level for maths and writing between the control and intervention groups. However, fewer participants in the intervention group (n = 4) than in the control group (n = 16) experienced a decrease in reading expectation.

Objective 11: estimate the standard deviation of the primary outcome to inform a sample size calculation for a full randomised controlled trial

Optimum reductions in daily sitting time that lead to health benefits have not yet been established in children. Current UK guidelines for children simply state that ‘all children and young people should minimise the amount of time spent being sedentary (sitting) for extended periods’.23 Recent data in adults have shown that reallocating 30 minutes of sedentary time per day to light movement is associated with a 2–4% improvement in cardiometabolic biomarkers.114 In the absence of current information on optimum reductions of sedentary time for health benefits in children, we are guided by the evidence above from adult studies.

The likely primary outcome in a definitive trial would be change in average daily (school day) sitting time, measured by the activPAL (or ActiGraph worn on the thigh, following feasibility testing), after 10 months. The study would be powered to detect a difference of 30 minutes per day between the intervention arm and the control arm. The primary analysis would be performed using linear multilevel models.115

Under the following assumptions, a sample size of 924 participants (462 participants/arm) from 42 clusters (21 clusters/arm) would be needed for this definitive trial to have 90% power to detect a change in mean total daily (school day) sitting time of 30 minutes per day at the 5% significance level (two tailed):

• SD of 95 (observed in our pilot study), which equates to a standardised difference of 0.316 (postulated true difference ÷ SD)116
• average cluster size of 22 (observed in this pilot study)
• conservative ICC of 0.05 (owing to the lack of previous data to inform this, we have followed recommendations by Campbell et al.117)
• coefficient of variation to allow for variation in cluster sizes of 0.11 (based on cluster sizes in this pilot, average of 22 and a range of 18–28).

Inflating the sample size by 25% to allow for potential individual loss to follow-up and non-compliance with the primary outcome (informed by the present study and recent school-based cluster RCTs118,119), and inflating the number of clusters per arm by 1 to allow for whole-cluster dropout, the study would require a sample size of 1276 participants from 58 clusters in total (638 participants and 29 clusters/arm).

Summary

The following chapters present the results relating to other aspects of this pilot trial. The preliminary economic evaluation is presented in Chapter 4 and the process evaluation is described in Chapter 5. A discussion of the overall findings, lessons learnt from this pilot trial and recommendations for further research are presented in Chapter 6.