In other words, the individual longitudinal data can be equated with the representative homogeneous cohort data. These categories (2 x 2 x 5 x 6) yielded 120 synthetic cohorts. Thus, the parameters were set to take into account the trade-off between homogeneity and representativeness. A change in the sex of the people concerned is extremely rare, but changes in race or colour are more common, since this variable is defined by the respondents, who may change their mind as to their race or colour.