Table 1.

Description of strength of evidence ratings.

Level of evidence	Description
Consistent evidence	>50% of observations find a significant association in one direction, with no substantial significant findings in the opposite direction for variable is examined by ≥3 studies
Some evidence	30–50% of observations find a significant association in one direction, with no substantial significant findings in the opposite direction for variables examined by ≥3 studies
Unlikely association	<30% of observations found a significant association in one direction for variables examined by ≥3 studies
Insufficient studies	Variables examined by <3 studies