Table 2.

Features of hair colorant use and NHL incorporated into the cohort study

Study	Region	Research period	Cohort group	Age, years	Cohort study cases, n	Exposure cases, n	NHL evaluation criteria	Hair colorant use evaluation standard	Adjustment factor	Newcastle-Ottawa Scale quality score
Mendelsohn [9], 2009	China	1996–2000	General population survey	40–70	73,366	51	Case history	Questionnaire survey	Occupational history; smoking history; drinking history;gender; age	7
Altekruse [5], 1999	USA	1982–1994	General population survey	>30	547,586	763	Pathological diagnosis	Questionnaire survey	Age; race; education; smoking history	8
Grodstein[10], 1994	USA	1976–1990	Inpatient registration	30–55	99,067	114	Pathological diagnosis	Questionnaire survey	Age; gender; smoking history	7