Ma et al. Respond to "Birth Certificates—A Best Control Scenario?"

Xiaomei Ma1 , Patricia A. Buffler2, Michael Layefsky3, Monique B. Does2 and Peggy Reynolds4

1 Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT.
2 Division of Public Health Biology and Epidemiology, University of California, Berkeley, CA.
3 Public Health Institute, Oakland, CA.
4 Environmental Health Investigations Branch, California Department of Health Services, Oakland, CA.

Received for publication February 23, 2004; accepted for publication March 3, 2004.

We appreciate the thoughtful commentary by Ross et al. (1) on our manuscript in this issue of the Journal (2). We are encouraged by their plan to assess the feasibility of obtaining birth certificates for control selection nationwide.

The focus of our manuscript was on comparing birth certificate controls and friend controls with reference to a population sample of births. We used parental ages, parental education, mother’s reproductive history, and birth weight to make these comparisons. Ross et al. suggested that it would be interesting to see how comparable the different control groups would be with respect to additional variables, including maternal cigarette smoking, alcohol consumption, and method of delivery, for example. Unfortunately, California birth certificates do not include information on cigarette smoking or alcohol consumption. We had not considered method of delivery (vaginal vs. cesarean section) a factor of etiologic significance, and we did not observe notable differences when we compared this factor between the control groups. In response to a comment from one reviewer of our manuscript, we evaluated two variables related to prenatal care—the month in which prenatal care was started and the total number of prenatal visits. The results were consistent with what was observed for the variables already included in the manuscript.

For the subset of the 64 cases and their matched birth certificate controls, we also compared the characteristics of potential controls who were initially selected for one of the cases but did not participate with those of the actual participating controls, that is, the replacement control for the nonparticipating controls. The characteristics we evaluated included not only the variables from the birth certificates but also neighborhood socioeconomic characteristics based on the 1990 US Census block group, including median family income, the percentage of the population older than age 18 years with a high school degree, and the percentage of the population older than age 25 years with a bachelor’s degree. We obtained the neighborhood data by linking maternal residence addresses listed on birth certificates to census block groups using a geographic information system. The results we observed were reassuring since the nonparticipating controls and their replacements were comparable with respect to all of the characteristics evaluated.

The assessments we have conducted to date are based on a relatively small sample. We plan to conduct similar evaluations on a much larger scale as the study continues. The Northern California Childhood Leukemia Study was recently funded for an additional 5 years of case ascertainment. We expect to enroll over 1,100 cases and a larger number of controls throughout the study. We hope that additional information from our study, the study planned by Ross et al., and possibly similar studies by other investigators will help further assess the theoretical and practical advantages and disadvantages of control selection using birth records in case-control studies of childhood diseases.


    NOTES
 
Correspondence to Dr. Xiaomei Ma, Department of Epidemiology and Public Health, Yale University School of Medicine, 60 College Street, New Haven, CT 06520-8034 (e-mail: xiaomei.ma{at}yale.edu). Back


    REFERENCES
 TOP
 REFERENCES
 

  1. Ross JA, Spector LG, Olshan AF, et al. Invited commentary: birth certificates—a best control scenario? Am J Epidemiol 2004;159:922–4.[Free Full Text]
  2. Ma X, Buffler PA, Layefsky M, et al. Control selection strategies in case-control studies of childhood diseases. Am J Epidemiol 2004;159:915–21.[Abstract/Free Full Text]

Related articles in Am. J. Epidemiol.:

Control Selection Strategies in Case-Control Studies of Childhood Diseases
Xiaomei Ma, Patricia A. Buffler, Michael Layefsky, Monique B. Does, and Peggy Reynolds
Am. J. Epidemiol. 2004 159: 915-921. [Abstract] [FREE Full Text]  

Invited Commentary: Birth Certificates—A Best Control Scenario?
Julie A. Ross, Logan G. Spector, Andrew F. Olshan, and Greta R. Bunin
Am. J. Epidemiol. 2004 159: 922-924. [Extract] [FREE Full Text]  




This Article
Extract
FREE Full Text (PDF)
Alert me when this article is cited
Alert me if a correction is posted
Services
Email this article to a friend
Related articles in Am. J. Epidemiol.
Similar articles in this journal
Similar articles in ISI Web of Science
Similar articles in PubMed
Alert me to new issues of the journal
Add to My Personal Archive
Download to citation manager
Search for citing articles in:
ISI Web of Science (1)
Disclaimer
Request Permissions
Google Scholar
Articles by Ma, X.
Articles by Reynolds, P.
PubMed
PubMed Citation
Articles by Ma, X.
Articles by Reynolds, P.