Statistical analysis
The primary exercise measures were average daily steps, average daily
MVPA measured by the pedometer, and the PAQ questionnaire score.
Activity values that were extreme (2 standard deviations above or below
average) were discarded to account for any technical errors or induced
bias.
Associations between the average daily steps, average MVPA and PAQ
score, with PFT and MRI measures, were conducted using Spearman
correlations. We interpreted the absolute values of correlation
coefficients as the following: 0.10-0.39 (weak), 0.40-0.69 (moderate),
0.70-0.89 (strong), and >0.9 (very strong)
associations26. All statistical analyses were carried
out using R version 4.0.3 (R Core Team, Vienna, Austria).
Separate multiple linear regression analyses were conducted to assess
the association between each of our primary outcomes (average daily
steps and average daily MVPA), respectively, with predictors of
interest, including history of BPD (yes/no), FEV1% predicted and MRI
total proton density. Sensitivity analyses examining the impact of
recruitment site were conducted for each multiple linear regression.
Unadjusted and adjusted estimates with 95% CI were reported.
To explore the impact of ADHD medication use on daily step count, we
conducted an exploratory descriptive analysis comparing daily step count
between children taking ADHD medication and those not taking ADHD
medications, as well as a subgroup analysis only within the group with
BPD.