The 24 identified sources included 8 articles and 16 book contributions from the years 1886 to 1958.
Most sources were published within the first quarter of the 20th century.
The studies in a meta-analysis are usually quantitative in design, with a preference for randomized-controlled trials.
It is important that the studies in a meta-analysis are very similar in their topic, hypothesis and design, so they can be aptly compared.
It usually includes only quantitative studies although some sources suggest that it can include both quantitative and qualitative studies.
This type of review aims to overcome possible biases by following a strict method.
Commonly identified OMT techniques included mobilization techniques, lymphatic pump techniques, and other manipulative techniques predominantly in the cervical and thoracic regions.
The wealth of OMT techniques for patients with pertussis that were identified suggests that pertussis was commonly treated by early osteopaths.
This type of literature review potentially provides the best evidence in the hierarchy of reviews.
A note for those looking to publish: editors often lean towards accepting a meta-analysis article, as it will likely yield more citations for their journal (for more details on this subject, see the article on impact factor).