Statistical analysis
Comorbidity
REGRESSION
The power analysis was calculated based on readmission rates of 22% in the control group and 12% in the intervention group [Data management and statistical analysis plans were conducted prior to the study.We used chi-square tests to describe and compare the baseline characteristics. When observations were not normally distributed, Wilcoxon rank-sum or Kruskal–Wallis tests were used.A binary regression model was used to compare the 30-day readmission risk, 30- and 90-day mortality rates, DAOH and DAOHGP between the two groups. The 30-day readmission analysis was performed based on the first readmission. The relative risk (RR) with a 95% confidence interval (CI) was calculated. The statistical models were adjusted for covariates with a statistically significant difference between the intervention and control groups at baseline.In this study, selection bias may be present, as the intervention and control groups were identified differently. Furthermore, identifying patients not receiving the allocated treatment was only possible if they were in the intervention group, not if they were in the control group. To mitigate selection bias and ensure the highest level of homogeneity between the groups, the analysis was based on data from all patients who met the inclusion criteria—that is, we analysed the effect of the assignment to the intervention at baseline rather than the effect of adhering to the intervention.Furthermore, for the primary outcome, analyses were performed in the following sub-groups: age group, gender, housing, civil status, social status, length of stay, Charlson Comorbidity Index (CCI), home care after discharge from index admission, municipality, blood samples at discharge, body mass index, admission year, vital signs at discharge, polypharmacy (five or more daily medicines [The Aalen–Johansen estimator displayed the mortality-adjusted cumulative incidence of 30-day readmissions. Both 30 and 90-day mortality rates were displayed using the Kaplan–Meier survival estimator.DAOH was calculated by subtracting the days spent in the hospital (in the period within 30 days after discharge from index admission) from 30. DAOHGP was calculated as above, but visits to the GP were also subtracted. DAOH and DAOHGP were analysed as binary variables with cut-offs at ≥ 23 days.Difference-in-difference (before and after) analysis was calculated based on 30-day readmission rates in patients who met the study inclusion criteria in all four participating municipalities in the pre-intervention period from 2015 to 2016. These data were compared to the 30-day intervention readmission rates. The results are presented as risk difference with standard errors (SEs) and p-values between the groups for 30-day readmissions.The CCI scores were calculated based on International Classification of Diseases-10 diagnostic codes of 19 conditions [STATA version 17 [