Table 1.

Critical appraisal

Study, year	1. Well-defined study groups	2. Selection bias adequately excluded	3. Exposition well defined and adequate method of examination of the exposition	4. Outcome well defined and adequate method of appraisal of the outcome	5. Outcome defined blind before knowledge of the exposition	6. Follow-up long enough	7. Adequate exclusion of selective loss-to-follow-up	8. Most important confounders or prognostic factors are known and taken into account in study design and analysis	Assessed quality
Adunsky [23]	Yes	Yes	No	Unclear	Unclear	Yes	Unclear	No	Low
Brouquet [20]	Yes	Yes	Yes	No	No	Unclear	Yes	No	Low
Marcantonio [7]	Yes	No	No	Yes	Unclear	Yes	Yes	No	Low
Morrison [9]	Yes	Yes	No	Yes	Unclear	No	Unclear	Yes	Moderate
Nandi [21]	Yes	No	No	No	Unclear	Yes	Yes	No	Low
Shiiba [22]	Yes	Unclear	No	Unclear	Unclear	Unclear	Unclear	No	Low