Categorisation of continuous risk factors in epidemiological publications: a survey of current practice

Table 2 Categorisation characteristics of the main continuous risk factor.

*Categorisation Characteristics*	*Number of Articles* *n = 50*
Number of categorisations used
One	38 (76%)
Two	12 (24%)
Three or more	0
Number of categories ^a
2	3 (6%)
3	9 (18%)
4	17 (34%)
5	13 (26%)
6	4 (8%)
7 to 10	3 (6%)
Unknown^b	1 (2%)
Choice of category boundaries
Quantiles	17 (34%)
Equally spaced intervals	9 (18%)
External criteria	6 (12%)
Other	17 (34%)
Unknown^b	1 (2%)
"Zero/Never" category	10 (20%)
Presentation of categorical results
Tables only	37 (74%)
Figures only	5 (10%)
Both Tables and Figures	5 (10%)
Neither	3 (6%)

For the sub-set of articles where categorisation was performed (n = 50 articles).
^a Of primary form of categorisation when more than one form was used
^b One article stated that categorisation was used but no results were presented