Analysis of Epidemiological Data

Likelihood Function (Poisson Regression). Assume we have cancer incidence (or mortality) data in tabular form for y = 1,. .., 7 calendar years, covering i = I,. .., I age groups. For each age group, the number of cancer cases diagnosed during calendar year j can be assumed to follow a Poisson distribution with mean  

The overall likelihood L for the observed incidence in all age-calendar year groups is given by 

The likelihood can be used to estimate not only the secular terns (birth cohort and period effects), but also the parameters of the biologically based model. In addition, if the data can be broken further by carcinogen(s) exposure (dose and duration) by age and period, one can also estimate in principle dose-response parameters. 

Individual Data. In this section we briefly describe how to compute the likelihood function in case we have cancer incidence (or mortality) data with detailed individual exposure information. 

Likelihood Function. For prospective cohort data, the likelihood function is the product of individual likelihoods over aU the subjects in the cohort. Assuming that participants are cancer free at their age of entry the study (ac ), and that we censor individuals in case of death from other causes or in case they survive cancer until the end of follow-up, the individual likelihoods are given by 

---

Hill WJ, Ferguson WS. 1979. Statistical analysis of epidemiological data from a chromium chemical manufacturing plant. J Occup Med 21 103-106. 

Axelrad, D. A., Bellinger, D. C., Ryan, L. M., Woodruff, T. J. (2007). Dose-response relationship of prenatal mercury exposure and IQ an integrative analysis of epidemiologic data. Environ. Health Perspect. 115 609—615. 

The first hint about the role of polyphenols in cancer was obtained through analysis of epidemiologic data. Several studies showed that tea, soy, olive oil, and whole grains consumption significantly reduces the risk of certain types of cancer. A study by Sun et al. conducted in eight countries showed that tea consumption reduces the risk of breast cancer (Sun et al. 2005). In addition, a prospective study by Severson and coworkers (1989) demonstrated a positive relationship between soy consumption (as tofu) and a decreased risk of prostate cancer. A much broader epidemiologic study on men in 59 countries demonstrated that a diet... 

Kelsh MA, Alexander DD, Kalmes RM, Huffier PA. Personal use of hair dyes and risk of bladder cancer a meta-analysis of epidemiologic data. Cancer Causes Control 2008 19(6) 549-58. 

G. A. AvRuskin, G. M. Jacquez, J. R. Meliker, M. J. Slotnick, A. M. Kaufmann, and J. O. Nriagu, Visualization and exploratory analysis of epidemiologic data using a novel space time information system. International Journal of Health Geographies, 3 (26), 2004. 

Analysis of epidemiological data shows that the increased risk of gastric cancer more than 20 years after gastric resection or vagotomy and in patients with pernicious anaemia is due to chronic atrophic gastritis and is not a consequence of decreased acid secretion or hypergastrinaemia. 

The assignment of the patient to a par- (h) ticular therapeutic strategy is not decided in advance by a trial protocol but falls within current practice and the prescription of the medicine is clearly separated from the decision to include the patient in the study. No additional diagnostic or monitoring procedures shall be applied to (i) the patients and epidemiological methods shall be used for the analysis of collected data ... 

There is some USEPA precedent for use of statistical meta-analysis in a regulatory context, including the recent meta-analysis of organophosphate-related acetylcholinesterase inhibition data and meta-analysis of epidemiological studies on effects of 2nd hand tobacco smoke exposure. Warren-Hicks and Moore (1998) provide some discussion of the potential applicability of meta-analysis to ecological risk assessments. 

Several species and populations from other Anopheles complexes have been discriminated based on CHC patterns. Examples include all five species of the An. quad-rimaculus complex (Carlson et al., 1997), some species of the An. maculipennis complex (Phillips et al., 1990a), malaria-vector and non-vector forms of the An. maculates complex (Kittayapong et al., 1990, 1993), and An. Stephensi strains susceptible or resistant to DDT and malathion (Anyanwu et al., 1993, 1997). CHCs have been used in combination with isoenzyme analysis to successfully differentiate populations of An. darlingi (Rosa-Freitas et al., 1992). All these findings demonstrate that hydrocarbon analysis is a powerful tool for distinguishing mosquito species and populations. This is particularly important for disease vectors, since it can facilitate interpretation of epidemiological data and assist implementation of control measures. 

In 1983, Merrell Dow Pharmaceuticals, Inc. voluntarily removed Bendectin from the market because of the many product liability suits pending. However, subsequent in-depth analysis of epidemiological and scientific data indicated that the therapeutic use of Bendectin had no measurable teratogenic effects. Nevertheless, despite the overwhelming scientific evidence, a number of jury decisions were rendered against the company (providing an argument for tort reform). 

Epidemiological evidence of the overall association between analgesic abuse and the development of renal impairment is documented in nine case-control studies [16-18, 20-21,33-34, 36-38], two prospective cohort studies [39, 40] and two observational cohort studies [41, 42] published in the last decades (Figure 1). It is inherent to epidemiological studies however, that the observed association between chronic renal failure and analgesic consumption does not establish cause and effect. Moreover, serious flaws in study design and analysis of the data have to be considered and were discussed in several reviews (Table 1) [7, 43,44,45]. 

Darby S, Hill D, Deo H, et al. Residential radon and lung cancer—detailed results of a collaborative analysis of individual data on 7148 persons with lung cancer and 14,208 persons without lung cancer from 13 epidemiologic studies in Europe. ScandJ Work Environ Health 2006 32 (Suppl l) l-83. 

Ayoub et al. [1987] developed a quantitative stress-strain index, called the job severity index (lSl),from empirical task analysis and epidemiologic data for manual materials handling tasks. This index computes the ratio of job task physical demands to person physical capacities from several interacting variables. The appHcation of the JSl is also detailed in Ayoub and Mital [1991]. Also, Kondraske [1995] defines a quantitative measure of stress that can be applied to individual performance resources. In this measure, defined as the ratio of resource utilization to resource availability, an adverse effect maybe noted when the stress level exceeds a threshold, which may be different for different types of performance resources (e.g., strength, range of motion, etc.). 

Presentations and discussion in this session fully recognized that data bases on PAH either do not exist or do not offer sufficient quality. Calculation of emission factors was difficult because of a lack of homogeneous data. Risk assessment of the use of diesel fuel in transportation is nearly impossible in the U.S. given the paucity of epidemiological data related to PAH and their derivatives. In the same way, the basic question formulated at the beginning of the workshop whether polycyclics increased in exhaust as a function of the concentration of aromatics in the fuel, remains controversial. Standardization of sampling and analysis data and units is necessary before data bases can be built. 

Ayoub et al. (1987) developed a quantitative stress-strain index, called the job severity index (JSI), from empirical task analysis and epidemiologic data for manual materials handling tasks. This index computes the ratio of job task physical demands to person physical capacities from several interacting... 

In most instances, epidemiological studies to determine if an exposure to a substance results in a given effect take the form of cohort studies, in which two separate groups composed of exposed and unexposed individuals are studied. It is critical that the study be unbiased either by the way the participants are selected or by the marmer in which the outcome is tested. Another critical factor is whether the two groups are in fact similar in all essential respects, which could affect the outcome of the study, or that the differences are such that they can be taken into account either in the design of the ejq)eriment or in the analysis of the data. In order to judge the validity of a study, all of the relevant factors must be completely documented and available for review. 

Epidemiological data on human populations show a strong positive correlation between age-adjusted mortality from breast cancer and dietary fat intake in different countries of the world (Carroll Khor, 1975 Carroll, 1975) but, as in the experiments with animals, there does not seem to be a correlation with intake of essential fatty acids. More detailed analysis of the data showed a positive correlation with intake of animal fat, but little or no correlation with intake of vegetal fat (Carroll, 1975). Moreover, although breast cancer mortality is about 5 times as hi in Americans as in Japanese, the per capita intake of linoleic acid is reported to be about the same in both countries (Insull et al, 1969). In addition, an analysis of the fatty acid composition of adipose tissue showed a level of 16.5% linoleic acid in Japanese compared to 10.2% in Americans (Insull et al, 1969). 

Effective surveillance and monitoring systems have been developed to generate epidemiological data about the presence or absence of diseases and their prevalence. Such systems provide vital information about the spread of diseases that can be used in the control and containment of hazards (e.g. pathogens) or the demonstration of freedom from disease status. In fact, the analysis of surveillance data can produce early warning indicators and trends in disease patterns that can support the need for biosecurity contingency plans, such as import controls or the establishment of buffer zones. 

In most studies, phytoestrogen intake has been estimated by direct methods that evaluate food intake either by recall (food-frequency questionnaires -FFQs) or by record (food diary), and subsequently by composition databases based on information of this kind. Food-frequency questionnaires are widely administered to subjects involved in epidemiological studies. Their validity and reproducibility is considered sufficient when statistically correlated to data obtained from dietary records (a properly-completed and comprehensive food diary) and from analysis of blood and urine samples (Kirk et ah, 1999 Huang et al, 2000 Yamamoto et al, 2001 Verkasalo et al, 2001). FFQs can be repeated several times a year and may be administered to large populations. Such an approach provides an easy and low-cost method of assessing the... 

Lopman, B., Armstrong, B., Atchison, C., and Gray, J. J. (2009). Host, weather and virological factors drive norovirus epidemiology Time-series analysis of laboratory surveillance data in lingland and Wales. PLoS ONE 4, e6671. 

---