We divided the latter two into four equal categories for analysis.
The number of remaining teeth (range: 0-32) was categorized into 3 equal categories 22-322, 11-21, and 0-10 teeth).
This was recoded into four approximately equal categories containing 0 10, 11 20, 21 30 or 31+ local off-sales outlets and 0 3, 4 9, 10 19 or 20+ local public houses (pubs).
For analysis purposes, average daily television viewing data were classified into four roughly equal categories (<2 h/day, 2 4 h/day, 4 6 h/day and ≥6 h/day).
Participants were grouped into five roughly equal categories according to their frequency of whole grain consumption and into quintiles according to their cereal fibre intake.
First, by dividing the predictor into equal categories, then plotting the log odds of the outcome against the category means of the predictor and visually assessing the linear relationship.
However, even with equal categories for the two measures, if the distributions are not the same, then it is not possible to obtain a perfect correlation between the two measures [ 40].
For each promoter, the sequence from 2,200 basepairs upstream to 500 basepairs downstream of the transcription start site (TSS) was analyzed for CpG content, and five equal categories defined.
The ranked national distribution of area deprivation scores was divided into five equal categories by quintiles, and patients were assigned a deprivation category from one (most affluent, or 'rich') to five (most deprived, or 'poor'), on the basis of their postcode of residence at diagnosis.
This scale had the additional advantage, that for analysis, it could be divided into three equal categories, overcoming the problems associated with presenting a three point scale to participants, namely a loss of information through limited response options and a related reduction in reliability [ 23, 16, 25].
