Sub-analyses revealed that self-help interventions had a small-to-medium-sized effect on positive symptoms (d+ = 0.42, 95% CI: 0.13 to 0.72), a small-to-medium-sized effect on negative symptoms (d+ = 0.37, 95% CI: 0.07 to 0.66), and a small-sized effect on outcomes associated with the symptoms of psychosis such as quality of life (d+ = 0.13, 95% CI: 0.02 to 0.24).
These differences were not significant t 31) = −1.69, 0.73, 1.94, (all p > 0.05) (Table 1); these values did represent a medium-sized and small-sized effect r =.32,.13 and.33 respectively.
An intriguing finding of the study was the small sized placebo effect observed for patient reported outcomes.
However, considering the small sized placebo effect observed in this study, the results described should be viewed with caution.
One possible explanation would be that the grouping effects induced by our model might have removed false predictions with small or medium sized effects.
The target sample size is 320 participants, which is based on power calculations required to identify small to medium sized effects for the primary study hypotheses.
Detectable differences for all measures were between 0.30 and 0.43 standard deviation units (small to medium sized effects), which translated to detectable differences of 0.62 minutes of MVPA per hour, 1.63 minutes of sedentary time per hour, and 0.33 ml/kg/min of energy expenditure, assuming a conservative estimate of measuring 25 children per preschool.
Our previous genetic studies demonstrated that these lines differ in large part due to cumulative action of multiple quantitative trait loci (QTLs) of small to medium sized effects, confirming that these lines may present a valuable model of the polygenic form of leanness/obesity [ 17- 19].
For example, a meta-analysis of self-control training on self-control task performance found a medium-sized effect [ 81] and a recent meta-analysis of response-inhibition training, using similar tasks to those used in the current study, on health behavior found a small-to-medium sized effect [ 94].
This might be due to the filling effect of the very small sized particles of LWFs.
