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PubMed1995

Bone lead measured by X-ray fluorescence: epidemiologic methods.

In vivo X-ray fluorescence (XRF) measurement of bone lead concentration (XRF) has emerged as an important technique for future epidemiological studies of long-term toxicity. Several issues germane to epidemiologic methodology need to be addressed, however. First, sources of variability in measurements of bone lead need to be quantified, including imprecision related to the physical measurement itself and the variability of lead deposition over the two main compartments of bones (cortical vs. trabecular) and within each compartment. Imprecision related to the physical measurement can be estimated for each individual measurement based on the variability of the signal and background. Second, approaches to low-level data need to be debated. We argue for using the minimal detection limit (MDL) to compare instruments and interpret individual measurements; however, with regard to epidemiologic studies, we would abandon the MDL in favor of using all point estimates. In analyses using bone lead as an independent variable, statistical techniques can be used to adjust regression estimates based on estimates of measurement uncertainty and bone lead variability. Third, factors that can be expected to modify the relationship between bone lead and toxicity such as gravida history, endocrinological states, nutrition, and other important influences on bone metabolism, need to be identified and measured in epidemiologic studies. By addressing these issues, investigators will be able to maximize the utility of XRF measurements in environmental epidemiologic studies.

Bone and Bones↗
PubMed1982

Analytic epidemiologic methods for research on nosocomial infections: definitions and examples.

Two types of epidemiologic studies are presented: the cohort study and the case-control study. The fundamentals distinction between the two methods is in the definition of the population groups for study. The cohort approach identifies groups with different exposure histories, whereas the case-control approach begins with groups with different health and disease characteristics. The investigation in the cohort method involves collection of data on the disease experience of the various exposure groups from date of exposure to some later follow-up date. Data collection in the case-control study is concerned with the exposure history prior to the date of the identified health and disease status. Both approaches are satisfactory in general, but either may have distinct advantages in a given study, depending chiefly on the frequencies of exposure and disease and on the nature of biases inherent in available data.

Cross Infection↗