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Locating and Appraising Systematic Reviews
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
IN RESPONSE:
Dr. Castro and colleagues report the minimal overlap between journals indexed in LILACS and those indexed in MEDLINE. This suggests that the former may be a rich source of primary research as well as reviews. For persons who are concerned about comprehensive searching and have the skills and resources to use literature published in different languages, LILACS may be very valuable.
The terminology issue raised by Dr. Atkins highlights confusion in the field: Both the “test of homogeneity” and the “test of heterogeneity” are used in the literature. We agree with Dr. Atkins's interpretation of this test. We disagree, however, that examination of study results should be the focus when one is deciding whether to statistically pool data. Before the test of homogeneity or heterogeneity is even considered, clinical judgment is required to evaluate study characteristics. One of the most important steps in a systematic review is assessment of the similarities or differences among studies, focusing on populations, interventions, and outcomes. At this point, on clinical grounds, reviewers may abandon the idea of statistically pooling study results in favor of a more descriptive and interpretive summary. If synthesizing study results does seem reasonable, the next step is testing whether the differences in results are greater than that which would be expected on the basis of chance alone. A significant positive test result can correlate with a clinically trivial degree of heterogeneity, and a negative test result does not rule out a clinically important degree of heterogeneity. Nevertheless, reviewers may decide not to statistically pool data if the test result is positive, or they may proceed to conduct sensitivity analyses or subgroup analyses (ideally on the basis of a priori issues identified as possible sources of variability).
For further discussion about issues of homogeneity and heterogeneity, we refer readers to other articles in the Annals' systematic review series [1, 2].
Dereck L. Hunt, MD
K. Ann McKibbon, MLS
McMaster University; Hamilton, Ontario L8N 3Z5, Canada
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
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