Many of the above papers overlap and the total number of papers
for these various searches was 525 journal articles published since
1977. This study was not intended to be an exhaustive list but simply a
list created by a chosen and competent method of sampling the
literature. Supplemental methods will increase the numbers but are
not expected to greatly change the observed relative contributions of
journal articles and citations. The focus here, however, was not a
comprehensive review but rather the choices of study and citation,
which is likely to be sufficiently covered by the method.