Table 2 Considerations for the interpretation of the unstructured multivariate linear model

Intervention effect

Estimates the difference in group scores at follow up, adjusted for all other included covariates. If coded to provide estimates for those who participated in the intervention wards, it assumes an interaction between group and time because this variable comprises 2 groups: 1) those who were in the control group at T1 and 2) everybody else (baseline sample and those who did receive the intervention at T1).

Hence:

\( intervention\ effect=\left\{\begin{array}{cc}\ 1& ifstudy\ group\ is\ control\ (0)\ and\ time\ is\ 1\\ {}\ 0& elsewhere\end{array}\right. \)

\( interventioneffect=\Big\{{\displaystyle \begin{array}{cc}1& ifstudygroupisintervention(1) andtimeis1\\ {}0& elsewhere\end{array}}\operatorname{} \)

Time

The models do not measure a main effect of time because as discussed above, an interaction between time and the intervention effect variable is assumed. The time variable allows an estimate of the adjusted change in the outcome between baseline and follow up. By changing the coding in the intervention effect variable, the estimates for the time variable are also restricted to the control group only or the intervention group only. As there is an interaction between group and time in the intervention effect variable, the effects within each treatment group are expected to be different over time.

Ward & Occupational status

The estimates for ward and occupational status are the mean outcome score differences between the different categories of ward and occupational status across time, given the assumption that both arms of the trial started with the same scores at T0. Therefore, for example, the estimate for occupational status is the mean score difference between the two categories of occupational status, adjusting for ward, time, and the intervention effect that forces the mean scores to be the same at baseline. The estimates for ward and occupational status are across time, and are not changed by recoding the variable for intervention effect.

Constant

The constant represents the estimated mean outcome score. As the models adjust for occupational status, this score is based on occupational status = 0 (direct care); and the reference category for ward, which was ward 1, where staff had the most negative perceptions of barriers to change. The constant is the same whether the intervention effect variable is coded to represent those who did, or those who did not receive the intervention because of the coding (which enforces a 0 treatment effect at baseline in order to meet the assumptions of an RCT).