Laura L. Perkins

Quality of Measurement of Smoking Status by Self-Report and Saliva Cotinine Among Pregnant Women

Objective. The objectives of this paper were to determine the rate of misclassification of smoking and nonsmoking status by self-reports and saliva cotinine of pregnant women participating in a smoking cessation trial, determine the relationship of the number of cigarettes smoked per day and saliva cotinine, and examine whether misclassification was due to an inappropriate saliva cotinine cutoff point. Methods. End of pregnancy self-reports of smoking status and saliva cotinine were used to calculate misclassification rates. Results. The findings revealed that 61 of 441 self-reported smokers had biochemical values inconsistent with smoking status for a smoking misclassification rate of 13.8%. The results also revealed that 28 of 107 self-reported quitters had cotinine values consistent with smoking status for a nonsmoking misclassification rate of 26.2%. Receiver Operating Characteristic (ROC) curves were then plotted to determine whether misclassification resulted from an inappropriate cutoff point. The cotinine cutoff point that maximized sensitivity and specificity for all women was 24 ng/ml. Racial ROC comparisons indicated a higher cutoff point for blacks than whites. Use of any of the ROC indicated cutoff points would not change the misclassification rates. Conclusions. These findings suggest that underreporting of smoking status during pregnancy is high and that social desirability of nonsmoking status may have contributed to the lack of precision in saliva cotinine to distinguish smoking status in this study.

The prevalence of women with breast implants in the United States—1989

Most estimates of the number of women with breast implants appear to be extrapolations of industry or clinical data. While both provide valuable information, the former about the total number of devices ever produced or sold and the latter about the cumulative number of surgeries performed, neither can be used to directly estimate the prevalence of women with silicone gel or saline implants. In 1989, Market Facts, Inc., conducted a mail survey of 40,000 households chosen as representative of the population of the United States and received responses from 70.7%. Overall, the prevalence was 8.08 per 1,000 women with about 60% of the devices reportedly implanted for cosmetic reasons. The procedure was more common among Whites of the higher socio-economic classes. Based upon the results of this survey, the total number of US women in 1989 with breast implants was estimated to be 815,700 (95% confidence interval: 715,757-924,729).

Breast implants and cancer: causation, delayed detection, and survival.

Concern for many women with breast implants has been focused on three topics: cancer (both breast and other cancers), delayed detection of breast cancer, and increased breast cancer recurrence or decreased length of survival. In this study, a qualitative review of the literature on these subjects was conducted, coupled with a metaanalysis of the risk for breast cancer or other cancers (excluding that of the breast). Researchers have consistently found no persuasive evidence of a causal association between breast implants and any type of cancer. The metaanalysis results obtained by combining the epidemiology studies support the overall conclusion that breast implants do not pose any additional risk for breast cancer (relative risk, 0.72; 95% confidence interval, 0.61 to 0.85) or for other cancers (relative risk, 1.03; 95% confidence interval, 0.87 to 1.24). This analysis suggests that breast implants may confer a protective effect against breast cancer. Women with implants should be reassured by the consistency of scientific studies which have uniformly determined that, compared with women without implants, they are not at increased risk for cancer, are not diagnosed with later‐stage breast malignancies, are not at increased risk for breast cancer recurrence, and do not have a decreased length of survival. (Plast. Reconstr. Surg. 107: 1393, 2001.)

Seven-year trends in pasma low-density-lipoprotein-cholesterol in young Adults: the CARDIA Study

To identify determinants of recent secular trends in lipids and characterize their influence on age-related increases in LDL-cholesterol, we examined a cohort of black and white men and women aged 18-30 in 1985-1986. Secular trends were determined by comparing participants aged 25-30 at baseline with those aged 25-30 at year 7 (2788 and 1395 participants, respectively). LDL-cholesterol was lower among those 25-30 at year 7 (5.9 to 10.2 mg/dL, depending on race-sex group; P < 0.001); weight was higher (8.3 to 12.5 lb; P < 0.001); Keys score was lower (-4.2 to -7.3 units; P < 0.001); and use of oral contraceptives was greater (white women only, P < 0.01). Among 4086 participants followed for 7 years, LDL-cholesterol changed little or decreased, despite substantial weight increases in all groups (11.6 to 19.0 lb; P < 0.001). Keys scores decreased by 6.1 to 8.0 units, and use of oral contraceptives decreased (P < 0.001). Declining secular trends in LDL-cholesterol occurred despite upward trends in weight; the decline was associated with lower dietary fat and cholesterol and offset expected age-related increases in LDL-cholesterol.

A meta-analysis of breast implants and connective tissue disease

Case reports have raised questions about an increased risk of connective tissue diseases (CTDs) among women with breast implants. From the reviews of more than 2,600 manuscripts, abstracts, and dissertations, this meta-analysis included 13 epidemiology studies that provided a relative risk (RR) estimate for the possible association between breast implants and CTDs. The meta-analysis summary RR was 0.76 for CTD in general (95% confidence interval [CI]: 0.55, 1.04; homogeneity p-value = 0.073) and was 0.98 for scleroderma (95% CI: 0.57, 1.64; homogeneity p = 0.006). Irrespective of which studies were aggregated in this meta-analysis, there was no significant increased risk for scleroderma, rheumatoid arthritis, or CTD in general. Conclusions from this study are consistent with the most recent review by the British Medical Devices Agency that found no scientific evidence to date of an increased risk of CTD associated with silicone gel breast implants.

Silicone gel breast implant rupture rates: research issues.

Documenting the rate of rupture of silicone breast implants appears to be deceptively easy. Largely because of the phenomenon of “silent rupture,” it isn’t. The authors explore the various technical biases (selection, misclassification, and confounding) and methodological problems that have plagued much of the research conducted to date. By means of a series of illustrations, they argue that explantation has limited utility. Noninvasive techniques have to be used to gather the proper type of data on the timing and frequency of these events. Only with the proper incidence data will researchers be able to identify better the different mechanisms underlying implant rupture and the relative importance of each. The authors recommend that better and standardized definitions of implant rupture be developed, that greater recognition be given to the technical biases and a greater effort be made to eliminate them from investigations of implant rupture, and that more research be conducted by multidisciplinary teams. Because of the growing awareness of the complexity of this issue, the authors also recommend that properly constituted advisory teams be used to provide comprehensive oversight of future research projects from beginning to end.

ESTIMATING A RELATIVE RISK ACROSS SPARSE CASE-CONTROL AND FOLLOW-UP STUDIES: A METHOD FOR META-ANALYSIS

Meta-analysis is the quantitative technique of combining results from different studies. There is a variety of procedures available for combining effect measures across epidemiologic studies. None of these methods provides an overall effect estimate when the data are sparse within studies and come from different study designs. In this paper we discuss the statistical relations between case-control studies and two types of follow-up studies. We use these relations to develop an exact methodology for combining results across study designs. We also use these relations to derive Mantel-Haenszel type formulae for summarizing results across studies. We illustrate these techniques with data pertaining to breast implants and connective tissue disease.

General mortality from 1944 through 1994 for a silicon-based chemical company.

The objective of this study is to reevaluate the statistically significant elevated risk of lung cancer among men with ≥20 years of employment at Dow Corning Corporation, a manufacturer of silicon-based materials. The cohort included 712 deaths among 8266 employees who were hired from 1943 to 1992 with follow-up through 1994. Standardized mortality ratios (SMRs) were calculated for 63 causes of death. Analysis confirmed a statistically significant increased mortality from cancer of the bronchus, trachea, and lung among men, prior to 1985, who jointly classified with ≥30 years of work duration and ≥30 years since first employed. SMRs for lung cancer after 1985, however, were not statistically significant and were inconsistent across work duration and years since first employed intervals. The study provides no evidence for elevated mortality among Dow Corning workers since the 1991 cohort mortality study. This study describes the updated mortality experience of a large employee cohort from a major silicon-based manufacturer. It illustrates that a well-designed mortality study can be a key component of employee health surveillance efforts in an industrial setting with potential hazardous workplace exposures.