Epiville

Bias

Student Role

Reading and understanding scientific articles takes a critical mind. You must carefully evaluate the methodologies employed and conclusions that are formed. At the end of the semester you will be asked to critique a published article. To start you on this path, below we illustrate an example of some of the core elements of a critique of a recently published paper on the association of self-reported residential pesticide use and breast cancer by Teitelbaum et al. (2007). Pay particular attention to the areas that are highlighted. If you have any questions, do not hesitate to discuss them with your seminar leader.

Synopsis

Susan L. Teitelbaum, Marilie D. Gammon, Julie A. Britton, Alfred I. Neugut, Bruce Levin, and Steven D. Stellman (2007). Reported Residential Pesticide Use and Breast Cancer Risk on Long Island, New York. American Journal of Epidemiology, 165:643-651.

Study Aim

To "investigate whether self-reported lifetime residential organochloride pesticide use increases breast cancer risk among women living on Long Island, NY between August 1996 to July 1997."

Null Hypothesis

Organochoride pesticides are not associated with breast cancer risk, i.e. an odds ratio of 1.0 comparing cases to controls on the probability of organochoride pesticides use.

Alternative Hypothesis

Organochoride pesticides are associated with increased breast cancer risk, i.e. an odds ratio greater than 1.0 comparing cases to controls on the probability of self-reported organochoride pesticides use.

Study Design

Type of study

The Long Island Breast Cancer Study Project is a population-based case-control study.

Study population

The study population consisted of all adult female residents of either Nassau or Suffolk Counties, residing in these areas between August 1, 1996 and July 31, 1997.

Method of selection/sampling of subjects:

Sources of data
Cases were identified through a 'super-rapid' identification network. This network "was established to ascertain potentially eligible case women with newly diagnosed breast cancer" from all hospitals in Long Island and three large tertiary care hospitals in New York City. Cases were included if their primary residence at the time of diagnosis (between August 1, 1996 and July 31, 1997) was in Nassau or Suffolk Counties of New York State. Controls were ascertained in two ways: among those <65 years of age, women were recruited through random digit dialing. Among those 65 years of age and older, women were recruited through Medicare and Medicaid rosters. Women were eligible to be controls if they did not have a lifetime history of breast cancer and lived in the two catchment counties between August 1, 1996 and July 31, 1997. Controls were frequency matched to cases at 5-year age intervals. Of the eligible cases, 74.3% completed the interview. Of the eligible controls, 62.8% completed the interview.

Measurements of exposures
Information included in the present study was collected through in-person structured questionnaires. Respondents self-reported lifetime exposure history to a vast array of potential chemical hazards that may increase risk for breast cancer. Questions elicited detailed information about the types of pesticides used, the duration and amount of use, the proximity of the respondent to the chemical, personal application of the pesticide (versus family member, etc.), and location of the pesticide use (home, lawn, garden, etc.). Questionnaires were administered by trained interviewers. Overall pesticide use (the sum of lifetime applications of all 15 categories), the two combined groups (lawn and garden and nuisance pest), and each of the 15 individual categories were considered in the analyses. Lifetime applications were categorized based on the control distribution.

Measurement of outcomes
Cases were women newly diagnosed with a first primary in situ or invasive breast cancer confirmed by the physician and the medical record. Controls were confirmed as not having had a history of physician-diagnosed breast cancer.

Measurement of potential confounders
To eliminate potential confounding effects of age, controls were frequency-matched to cases in the design stage of the study. Geographic location was controlled by restriction; only women residing in two specific counties were included for participation. Other potential confounders were measured via in-person structured questionnaires. These potential confounders included: "race, marital status, religion, household income, age at menarche, parity, age at first birth, lactation, menopausal status, oral contraceptive use, hormone replacement therapy use, first-degree family history of breast cancer, history of benign breast disease, body mass index (weight in kilograms divided by height in meters squared) at the reference age and at age 20 years, alcohol use, smoking status, and physical activity." Finally, highest level of educational attainment was included to eliminate potential confounding by socioeconomic status.

Findings

For the present module we will focus on the association between lawn/garden pesticide use and breast cancer. The numbers below were extracted from Table 1 of Teitelbaum et al. (2007). We use these numbers to calculate a crude (i.e., unadjusted) odds ratio.

 Breast cancer +Breast cancer -Total
Ever used lawn/garden pesticides1,2541,2312,485
Never used lawn/garden pesticides240305545
Total1,4941,5363,030

OR = (1254/240)/(1231/305) = 1.29

The odds of breast cancer among those who have ever used lawn/garden pesticides is 1.29 times that of those who have never used lawn/garden pesticides. Alternatively, the odds of ever using lawn/garden pesticides among cases is 1.29 times that among controls.

When controlled for age and educational status, the association between lawn/garden pesticide use and breast cancer was 1.34 (Table 1 in the text). This indicates that the odds of breast cancer among those who have ever used lawn/garden pesticides is 1.34 times that of those who have never used lawn/garden pesticides. The 95% confidence interval for this odds ratio ranged from 1.11 to 1.63, a fairly narrow interval indicating that the estimate has good precision. Furthermore, because the null hypothesis value of 1.0 is not included in the confidence interval, we can conclude that the evidence presented here does not refute the hypothesis that lawn/garden pesticide use is associated with breast cancer.