Statistical methods for the explorative part
REGRESSION
We will use the technique of Tian et al. [The constructed new index assigns weights to the selected variables. In order to facilitate the interpretation of these weights, we use two different representations. The first refers to the weights when all variables have been standardized to a standard deviation of 1.0. This allows to compare weights across variables: the higher the weight, the stronger is the association of the new index with this variable. The second refers to the weight when the variables are not standardized. These can be interpreted directly as regression coefficients: increasing the variable by one point implies a change in the benefit from chiropractic manipulation by this coefficient.In applying this approach, we neglected the candidate variable 