Instead of treating time as a continuous variable, which is more common in repeated measure multi-level modeling, two dummy variables representing Phase II, the immediate post-KPI period versus Phase III, the end of the OLI period, and the end of Phase III versus the 6-month follow-up, were created and incorporated as level one covariates.
The variable drug was represented in the model as two dummy coded contrast variables using the MDMA group as the reference group.
The construct "Reef zone" has been incorporated into the regression model as two dummy variables with "backreef" serving as the "reference group".
Time of measuring was represented in the model by two dummy variables for the measurements at 6 and 26 weeks.
The independent variables in each model are two dummy variables indicating the group, with the group of patients receiving usual care as the reference category and two dummy variables for time and their interaction effects.
The second model includes two dummy variables: one that is set equal to 1 if the blood lead level is 5 9 μg/dL; and one that is set equal to 1 if the blood lead level is ≥ 10 μg/dL.
All models included two dummy variables to adjust for whether physical functioning was assessed at two phases or only once at either Phase 8 or 9.
The explanatory variable 'familiarity' was included in the models with two dummy variables for 'moderately familiar' and 'very familiar', with 'not familiar' as reference category.
A multiple regression model with two dummy-coded predictor variables (early lessons, first instrument) accounted for 9% of the variance in overall performance, F 2, 194) = 9.44, p = .0001.0001
Under the co-dominant model, one can use two dummy variables or an additive model (G=0,1,2) to model the genetic effect.
