Readers should systematically assess methods used to identify, measure and analyze confounding in observational cohort studies.

OBJECTIVE: To describe techniques used to address confounding in published observational studies. STUDY DESIGN AND SETTING: A systematic literature review identified studies using administrative or registry data to investigate health effects of drug therapies. Studies published from January 2001 to December 2005 came from BMJ, New England Journal of Medicine, Lancet, Annals of Internal Medicine, and JAMA. A structured abstraction form was used to collect information about confounding. RESULTS: The search identified 29 studies. Twenty-two studies (76%) had 10,000 or more subjects and 18 (62%) used a mortality outcome. None mentioned use of a literature search to identify confounders, however, 28 (97%) listed confounders included, and 26 (90%) listed confounders not included in the study. Eighteen (62.1%) discussed the validity of confounder data. Most (22, or 76%) studies included a table with the distribution of confounders but none used effect size to assess imbalance between comparison groups. Almost all studies used regression techniques (28, or 97%); fewer used stratification (16, or 55%) or matching (four, or 14%) to address confounding. Eleven (40%) studies discussed sensitivity analyses. CONCLUSION: Published cohort studies routinely include a list of potential confounders but there is room for improvement in confounder identification, measurement, and analysis.

Use of paediatric versus adult oncology treatment centres by adolescents 15-19 years old: the Canadian Childhood Cancer Surveillance and Control Program.

The aim of this study was to evaluate the treatment patterns of adolescents with cancer in Canada to ensure this population is receiving the most appropriate care. The Treatment and Outcome Surveillance (TOS) system was compared with the Canadian Cancer Registry (CCR) to estimate the proportion of adolescents (15-19 years) treated in Canadian paediatric oncology centres from 1995 to 2000 inclusive. Using TOS, the demographic, disease, and clinical characteristics of adolescents treated in paediatric versus adult centres in the Prairies were compared and differences were tested statistically. Approximately 30% of Canadian adolescents with cancer were treated in a paediatric centre. Adolescents treated in an adult centre were older at diagnosis and more likely to have carcinoma or germ cell tumours. The time between symptom onset and first treatment was longer for these adolescents, primarily due to the time between first health-care contact and assessment by a treating oncologist or surgeon. They were less likely to be enrolled in a clinical trial. These results suggest that care for adolescents with cancer in Canada is less satisfactory than for younger children, and can be improved.