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Benzene Epidemiologic Studies on Types of Workers

From: Scientific Studies on Benzene Health Effects

Epidemiology

Definition: The study of diseases and their causes in groups of people who have had similar exposures to hazardous chemicals or other toxic agent or agents.

How we arrive at causation:

1. The odds are 19 to 1 that exposure to benzene caused cancer in the study population.
2. Most important is the method of the study and the analysis and judgment of the results.
3. If the probability (p) value between benzene exposure and cancer is 0.05 or less, it is more likely than not that an increase in cancer from benzene will occur.

Epidemiologists use statistics to determine whether or not there is a cause and effect relationship between a disease in groups of people who have had similar exposure to a toxic agent or agents.

As the world-renowned physician and epidemiologist, Irving Selikoff, said: "Statistics are human beings with the tears wiped away."

Types of Epidemiological Studies:

Case Control Study - Compares otherwise similar groups of people with and without disease.

Cohort Study - Compares people who have been exposed and people who have not been exposed.

Statistical Significance - A strong indication that an association between two or more events does not occur by chance. A likelihood of less than a 5% chance (5/100) is generally accepted as statistically significant and is written as p<0.05.

Some Statistical Methods To Avoid

In many traditional reviews, one can find the use of a qualitative tally or vote count. Consider the following:

1. "Of 17 studies to date, 5 found a positive association, 11 found no association, and one found a negative association. Thus, the sum of the studies favors no association."
2. This statement ignores the possibility of a weak positive association in 11 studies, a weak or absent association in the one negative study, and a strong association in the positive studies. The average association of the studies could have been positive.
3. A qualitative tally should never serve as anything more than a provocative introduction to a more detailed analysis.

From: Rothman KJ & Greenland S. Modern Epidemiology, 2nd Edition. Lippincott Williams & Wilkins.

Epidemiological Studies:

Sources: Aksoy et al., 1989; Bond et al., 1986; Decouflé et al., 1953; Delore et al., 1928; Goguel et al., l967; Goldstein, 1977; Hayes et al., l972; lnfante et al., 1985; 1995; McMichael et al., 1974, l975, 1976; Rinsky, 198l, l987; Savitz et al., 1997; Schwartz, 1987; Travis et al., 1994; Vianna & Polan, 1979; Vigliani et al., 1976; Wong, 1987; Yin et al., 1987, 1989, 1994, 1996.

Source: Acquavella (1991); Adelstein (1972); Berger & Manz (1992); Bond et al. (1985); Brown et al. (2002); Brownson et al. (1989); Creppi et al. (1997); Delahunt et al. (1995); Partenen et al. (1991); Goldberg MS et al. (2001); Greene et al. (1979); Hanis et al. (1979, 1982, 1985a,b); Lagorio et al. (1994); Lundberg & Milatou-Smith, 1998; Miller et al. (1986); Schnatter et al. (1993); Thomas et al. (1980); Yin et al. (1989).

From: Infante PF. 1995a. Benzene and leukemia: Cell types, latency and amount of exposure associated with leukemia. In: (Imbriani M, Ghittori S, Pezzagno G, Capodaglio E, Eds.) Update on benzene. Advances in Occup Med Rehabil. Fondazione Salvatore Maugeri Edizioni, Pavia, Italy. 1:107-120. Yin S-N, Li GL, Tain FD, et al. 1989. A retrospective study of leukemia and other cancers in benzene workers. Environ Health Persp 82:207–213.

Low level: <2 ppm TWA; Medium level: 2-9 ppm TWA;
High level: 25 ppm TWA.

From: Ott MG , Townsend JC, Fishbeck, WA, Langer RA. 1978. Mortality among individuals exposed to benzene. Arch Environ Health 33:3-10.

Bond GG, McLaren EA, Baldwin CL, Cook R. 1986. An update of mortality among workers exposed to benzene. Br J Ind Med 43:685–691.

From: Rinsky RA, Smith AB, Hornung R, et al. 1987. Benzene and leukemia: An epidemiologic risk assessment. N Engl J Med 316:1044–1050.
[Overall, SMR-5.6 (p<0.001) for leukemia]

HAYES (1997)

Hayes et al. (1997) evaluated a cohort of 74, 828 benzene-exposed workers and 35,805 unexposed workers employed from 1972 through 1987 in 12 cities in China to determine the incidence of hematologic neoplasms and related disorders. The results of that study indicated that benzene exposure is associated with a spectrum of hematologic neoplasms and related disorders as shown in the following tables.

Hayes RB, Yin S-N, Dosemeci M, et al. 1997. Benzene and the dose-related incidence of hematologic neoplasms in China. J National Cancer Inst 89:1065-1071.

Where RR = Relative risk, which is equal to 1.0 for unexposed workers. All risks adjusted for age and sex.

From: Hayes RB, Yin S-N, Dosemeci M, et al. 1997. Benzene and the dose-related incidence of hematologic neoplasms in China. J National Cancer Inst 89:1065-1071.

Li G-L, Linet MS, Hayes RB, et al. 1994. Gender differences in hematopoietic and lymphoproliferative disorders and other cancer risks by major occupational group among workers exposed to benzene in China. JOM 36:875-881.

* p<0.05; ** p<0.001

FLODIN et al. (1988)

In this Swedish study of patients with CLL, the relative risk of developing CLL in painters employed for more than one year was 4.0 (95% CI = 1.0-14.7). This represents a 300% increased risk.

Flodin U, Fredriksson M, Persson B, Axelson O. 1988. Chronic lymphatic leukaemia and engine exhausts, fresh wood, and DDT: a case-referent study. Br J Indust Med 45:33-38.

Chronic Lymphatic Leukemia and Engine Exhausts, Fresh Wood, and DDT: a Case-Referent Study.

In this Swedish study of patients with CLL, the relative risk of developing CLL in painters employed for more than one year was 4.0 (95% CI = 1.0-14.7). This represents a 300% increased risk.

(Source *: Flodin U, Fredriksson M, Persson B, Axelson O. (1988) Br J Indust Med 45:33-38.)

INFANTE (1995) concluded in his comprehensive review of leukemia cell types and benzene exposure that:

• "As a result of this review, it is apparent that all of the major types of leukemia and some of the more rare types of leukemia are associated with occupational benzene exposures...
• "... Myelodysplastic syndrome and myelofibrosis have been reported in association with benzene exposure.
• "In some case series, acute leukemia, predominately AML, was the most frequent form of leukemia reported while in other case series, chronic forms of leukemia were common."

From: Infante P, White MC. 1995. Assessment of leukemia mortality associated with occupational exposure to benzene. Risk Anal 4:9-13.

INFANTE's (1995) Conclusions in His Comprehensive Review of Leukemia Cell Types and Benzene Exposure*
"As a result of this review, it is apparent that all of the major types of leukemia and some of the more rare types of leukemia are associated with occupational benzene exposures . . . ". . . Myelodysplastic syndrome and myelofibrosis have been reported in association with benzene exposure. "In some case series, acute leukemia, predominately AML, was the most frequent form of leukemia reported while in other case series, chronic forms of leukemia were common."

From: Infante P, White MC. (1995) Assessment of leukemia mortality associated with occupational exposure to benzene. Risk Anal 4:9-13).

SAVITZ, D.A., Ph.D.on Causal Inference*
"Causal inference in epidemiology is recognized not to be a direct product of the research or something that is proven by the data, but ajudgment based on a constellation of evidence." "If we measure a relative risk of 2.0, and the confidence interval is 1.2 to 3.0, it would be declared 'statistically significant' though a relative risk of 2.0 with a confidence interval of 0.8 to 3.5 is saying virtually the same thing. In either case, the best estimate is that exposure doubles the risk of disease ."
(Source*: Page 4-6, Savitz Affidavit, November 24, 1999.)

SAVITZ, D.A., Ph.D.

"Causal inference in epidemiology is recognized not to be a direct product of the research or something that is proven by the data, but a judgment based on a constellation of evidence."

Page 4, Savitz Affidavit, November 24, 1999.

"If we measure a relative risk of 2.0, and the confidence interval is 1.2 to 3.0, it would be declared ‘statistically significant' though a relative risk of 2.0 with a confidence interval of 0.8 to 3.5 is saying virtually the same thing. In either case, the best estimate is that exposure doubles the risk of disease."

Page 5-6, Savitz Affidavit

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