Table 2. Approaches to analysis reported in 31 papers identified in the review that used Cox regression.

Description of method		Number of papers
Choice of timescale	time in study	22
	age	9
Analysis model	Cox weighted	20
	Cox unweighted	11
Weights used in Cox model	Prentice	10
	Barlow	7
	not stated	3
Robust standard errors used		17
Proportional hazards assumption		12