Primary outcome
SE
The null model at T0 had an Intra-Class-Correlation Coefficient of 0.093 meaning that the correlation of cumulated defined daily doses (DDD) of PPI at T0 among patients within the same practices is about this value. Consequently, most of the variation in the outcome is among the lower-level units and therefore, correlation between them is relatively lowAt T1 after the introduction of cumulated defined daily doses (DDD) of PPI at T0 as a covariate, the Intra-Class-Correlation Coefficient was reduced to 0.042. There was a significant difference between the two groups (p < 0.0001) in favour of the intervention group (Table Results for the multilevel model at T1 with cumulated defined daily doses (DDD) of PPI at T0 as a covariate (ANCOVA model).Compared to baseline (T0), there was a significant reduction in the PPI prescriptions after 6 months (T1) among study patients of intervention group (reduction of the mean PPI DDD: − 22.3% (95%CI − 18.55 to − 25.98), see Fig. Course of the adjusted means (adjusted at T1 and T2 by the ANCOVA models) of the DDD of PPI in the intervention and control groups (average DDD with standard errors).At T2 after the introduction of cumulated defined daily doses (DDD) of PPI at T0 and T1 as covariates, the Intra-Class-Correlation Coefficient was 0.05. There was no significant difference between the two groups (p = 0.48) (Table Results for the Multilevel model at T1 with cumulated defined daily doses (DDD) of PPI at T0 and T1 as covariates (ANCOVA model).Follow-up at T2 showed that reduced DDD PPI remained stable in intervention patients with no further significant change compared to T1: + 3.5% (95%CI − 0.99 to + 8.03. Control patients showed a decrease in prescribed DDD PPI of -10.17% (95%CI − 6.01 to − 14.33) at T2 compared to T1.The longitudinal random intercepts model confirmed the results of our multilevel ANCOVA models. The time effect was significant (estimate − 27.40, SE 3.36, p < 0.0001), as the number of DDD of PPI decreases over time. The group allocation did not show significance, as there was no significant difference between the intervention and control groups at both time T0 and time T2 (control, estimate − 1.32, SE 11.09, p = 0.91). The time*group interaction, on the other hand, was significant, as there was a differential trend with a significant difference at time T1 (estimate 15.82, SE 4.90, p = 0.001).There were no relevant differences between the models with complete cases and with imputed data.