Studies were classified according to an algorithm based on an established
method for classifying human health studies by epidemiological study type
(Kramer MS, Boivin JF. Toward an "unconfounded" classification of epidemiologic
research design. Journal of Chronic Disease 1987; 40(7):683-8) for
classification of epidemiologic studies. The figure below presents the
inclusion criteria and classification algorithm that is a modified version
of Kramer and Boivin's method.
For definitions, see the glossary.