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Archives of Environmental Health: An International Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/vzeh20
A Retrospective Cohort Study of Cancer Incidence among New York State Farm Bureau Members a
a
a
Dr. Alice D. Stark P.H , Hwa-Gan Chang M.S , Edward F. Fitzgerald Ph.D. , Karen Riccardi a
Ph.D. & Robert R. Stone Ph.D.
a
a
Bureau of Environmental and Occupational Epidemiology, New York State Department of Health , Albany, New York, USA Published online: 03 Aug 2010.
To cite this article: Dr. Alice D. Stark P.H , Hwa-Gan Chang M.S , Edward F. Fitzgerald Ph.D. , Karen Riccardi Ph.D. & Robert R. Stone Ph.D. (1990) A Retrospective Cohort Study of Cancer Incidence among New York State Farm Bureau Members, Archives of Environmental Health: An International Journal, 45:3, 155-162, DOI: 10.1080/00039896.1990.9936709 To link to this article: http://dx.doi.org/10.1080/00039896.1990.9936709
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
A Retrospective Cohort Study of Cancer Incidence among
Downloaded by [McGill University Library] at 07:34 12 January 2015
New York State Farm Bureau Members
ALICE D. STARK, Dr. P.H. HWA-GAN CHANC, M.S. EDWARD F. FITZGERALD, Ph.D. KAREN RICCARDI, B.S. ROBERT R. STONE, Ph.D. Bureau of Environmental and Occupational Epidemiology New York State Department of Health Albany, New York
ABSTRACT. Cancer incidence from 1973 through 1983 in 18 811 New York Farm Bureau members was examined using a retrospective cohort study design. The observed number of cancers for all age groups was 72% of the expected, and the major deficits in incidence occurred for lung (52% of expected), gastrointestinal (67%of expected), and bladder (78% of expected). Similar deficits have been reported by other researchers. Unlike other studies, we did not find a significant excess of cancer of any site. Given the healthy worker effect and the small numbers of incident tumors at some sites, the Standardized Cancer Incidence Ratios that were over 100 in value (i.e., lip, melanoma of the skin, prostate, multiple rnyeloma) merit further investigation. This study differs from previous research in population, setting, and method. Nonetheless, the general pattern of results is consistent with the findings of other investigations.
DESPITE a low overall cancer mortality rate, some investigators have found that farmers have disproportionately more deaths from certain tumors, e.g., prostate,’ skin,b non-Hodgkin’s lymphoma,’, and The results have led to the speculation that pesticides, zoonotic viruses, and other potentially carcinogenic exposures may be involved.ll Burmeister et al.4 found an increased odds ratio for leukemia in Iowa farmers in counties with the greatest numbers of egg-laying chickens and the largest number of acres treated with herbicides. Donham et al.3 also studied leukemia in Iowa and noted a highly positive correlation between acute lymphoid leukemia in males and cattle density. The relationship was greater for dairy cattle than for beef cattle. Mortality from non-Hodgkin’s lymphoma’ was MaylJune1990 [Vol. 45 (No.3)]
increased among farmers in Wisconsin (U.S.A.), especially in counties with high summary measures of general agricultural activity, small-grain acreage, wheat acreage, and acres treated with insecticides. A recent report by Reif et a1.,l0 which evaluated occupational risks for brain cancer, identified an increased risk among farmers; the highest risk was found for livestock farmers. Relatively few studies have examined these issues from the perspective of cancer incidence, and they have emphasized malignancies of the hematopoietic and nervous tiss u e ~ . ~Hoar , ~ ~et, a1.12 ~ ~ studied soft-tissue sarcoma, Hodgkins disease, and non-Hodgkin’s lymphoma in Kansas. Farm use of phenoxyherbicides was associated with nonHodgkin‘s lymphoma; frequent use increased risk. Neither soft-tissue sarcoma nor 155
Downloaded by [McGill University Library] at 07:34 12 January 2015
Hodgkin’s disease was associated with pesticide exposure. Pearce et aI.l3 did not find an association between non-Hodgkin’s lymphoma and exposure to phenoyxherbicides or chlorophenols. However, fencing work that necessitated exposure to risk factors, including arsenic and sodium pentachlorophenate, increased risk, as did employment in a meat works. The postulated risk factors in the meat works were 2, 4, 6-trichlorophenol and zoonotic viruses. There was significant interaction between the risks associated with these two activities. An Italian study8 of brain gliomas identified an increased risk for farmers. The increase in risk was attributable to use of insecticides and fungicides. Many farmers who were exposed to fungicides reported using commercial compounds of copper sulfate, some of which contained methyl urea, which has produced cancers of the nervous system in animals. The current study differed from previous research in that it focused on New York State, included only farm owners and operators, and utilized a retrospective cohort design to examine cancer incidence from 1973 through 1983. It followed the format of a previous report,14which examined overall mortality in the same cohort. Farming in New York State. According to the United States Census of Agriculture, there were 49 273 farms in New York State in 1978,15and the average size of each was 201 acres. Of these farms, 89% were individual or family operations, and 2% were incorporated. Reflecting this is the fact that in 1978, 65% of the state’s agricultural labor force consisted of family members who worked an average of 50 h/ wk.16 The average age of the farm operator was 50 y, and 94% percent were male. Ninety percent of these operators resided on their farms. New York State farms sold $2.19 billion worth of commodities in 1979. Dairy products accounted for 57.1%, fruit crops 8.3%, field crops 7.8%, vegetables 7.4%, and greenhouse and nursery products 4.6%. Materials and methods Study cohort. The study cohort was identified from the membership lists of the New York Farm Bureau obtained for 1973 through 1979. The Farm Bureau is a voluntary organization that was established in 1910. It represents the economic and political interests of farmers in New York State and provides group insurance plans, discount purchases of equipment, and other benefits. In 1973, the Farm Bureau had 11 627 regular members, and by 1979, the number had grown to 17 717. All farm owners and operators in New York State whose gross annual sales are at least $10 000 are eligible for membership; approximately 73% of this number belong to the Farm Bureau, using the 1978 United States Census of Agriculture data as the den0minat0r.l~The New York Farm Bureau’s philosophy is that members be active farmers and that the proportion of associate (nonfarmer) members be kept under 10%. Associate members were excluded from this study. 156
Fewer than 1% of the farmer members are not engaged in full-time physical labor on their farms (personal communication, New York Farm Bureau). Because the number of members who were female or who were less than 18 y of age was so low, these members were omitted from the study cohort. Persons who discontinued membership during the study period, however, were included under the assumption that even if they were no longer farming, exposures that they had incurred as farmers could affect their cancer experience. The result was a cohort of 20 833 males who were at least 18 y of age and who had been Farm Bureau members for at least 1 y during 1973-1979. Fifty-eight percent of the cohort had been members for all 7 y. Turnover resulting from dropouts was not a major problem, but increasing enrollment in the Farm Bureau over time reduced the average length of membership, i.e., 85% of the cohort was listed in 1979, compared with only 60% in 1973. Farmers also occasionally failed to renew membership in a given year but were reinstated subsequently, which resulted in a total duration of less than 7 y. Table 1 shows the age distribution of this cohort (mean = 44 y) at time of entry into the study, When comparing data from the 1978 United States Census of Agriculture to the study group, the study participants were relatively young.15 For example, 2.2% of census-designated farm operators in New York were less than 25 y of age v. 8.3% of the Farm Bureau cohort. Conversely, 19.2% of farm operators in the census were 65 y of age or older, compared with 8.5% for those in the current investigation. Data obtained from the membership lists included name, address, and type of farm. The number of years of membership was not available, and it was not possible to examine membership lists prior to 1973 because they were neither computerized nor centrally accessible. We could not, therefore, assess for each person the duration of his employment as a farmer. According to the Farm Bureau, however, their members have engaged in farming for a median period of at least 20 y (personal communication, New York Farm Bureau). Several methods were used to follow the cohort from 1973 through 1983 and to determine cancer incidence. A computer search of New York State Department of Motor Vehicles files for the last year of application or renewal for operator licenses and registrations was conducted. This procedure identified the most recent year that a participant was a resident of New York State and his date of birth. Once birthdates were obtained, deceased members of the study cohort were identified by computer matching with the New York State Bureau of Health Statistics death certificate files for 1973 through 1983. Definite matches required the agreement of name, county of residence, and birthdate ( 2 1 y). We were able to use strict criteria because of the reliability of the sources used for cohort identification. A final computer search matched the farmer cohort with New York State Cancer Registry files to Archives of EnvironmentalHealth
Table 1 .-Number ( n ) and percentage (%) of New York Farm Bureau Cohort, by Age at Entry into Study: 1973-1 979
Age fy)
n
1 729 4 295 4 604 4 959 3 485 1 345 41 6 20 a33
Downloaded by [McGill University Library] at 07:34 12 January 2015
18-24 25-34 345-54 55-64 65-74 75 + Total
%
8.3 20.6 22.1 23.8 16.7 6.5 2.0 100.0
identify cohort members who had been diagnosed with cancer. Because it was important to ascertain cancers in the study and comparison populations in an identical manner, only cases identified through the Cancer Registry were counted. The registry has been in existence since 1940 and includes all cases of cancer, excluding nonmelanoma skin cancer. It is more than 95% complete17for upstate New York, exclusive of New York City. The Cancer Registry and the death certificate files are periodically crossmatched to insure completeness of both databases. The matching rules for cancer were the same as for deaths. Tumor site, date of and age at diagnosis, stage, and histology were abstracted. To update the status of persons not found to be deceased, Farm Bureau membership lists were searched in reverse chronological order from 1980 through 1984 or to the most recent year in Motor Vehicles records. Comparison population. The comparison group potentially consisted of the 2 903 788 men who were at least 25 y of age who resided in New York State, exclusive of New York City, as enumerated by the 1980 U.S. census. The minimum age was 25 instead of 18 to allow for the 7-y difference between the first date of entry into the study and the date of the census. We first excluded from the comparison population the 47.8% who lived in towns that had at least two-
thirds of their area designated as urban. The reason for this exclusion was to avoid confounding any farmer-cancer incidence associations with urbanrural differences. For consistency, we also excluded from the study the 5.0% of Farm Bureau members who had an urban mailing address. Some approximations were necessary in using the 1981 National Zip Code Directory18and the 1980 Gazetteer of New York Statelgto identify towns of residence from the mailing addresses on the Farm Bureau membership lists. (The town was the smallest geographic unit studied because the accuracy of the residential information noted on vital records i s limited for smaller areas. Note that the entire area of New York State i s divided into towns. Towns reflect a geographic rather than a population density designation and may, in fact, be rural in nature.) If an owner or operator's zip code referred to a village, the entire town of which the village was a part was eligible for the comparison population. For villages divided between two towns, the first town listed in the Gazetteer was assumed to be where the farmer lived. If a mailing address for a farm owner or operator referred to a name for which there was both a town and a city, only the town was eligible for inclusion. If a town did not have or share a post office, it could not be eligible for the comparison population. In addition, another 26.5% who lived in towns with 10 or fewer Farm Bureau members were eliminated from the comparison population. This was done because the objective of this study was to compare the cancer experience of'farm owners and operators with that of men who resided in the same towns as the farmers, thereby isolating the effects of occupational exposures from more general environmental influences. Because these towns had proportionately very few farmers, they were not representative of the communities in which the farmers lived. The 4.9% of the Farm Bureau members with mailing addresses in these towns were similarly deleted. The net effect was to eliminate urbanized areas and rural towns without Farm Bureau members. As noted in Table 2, the result was a comparison population of 747 128 men and a study cohort for analysis of 18 811
Table 2.-Construction of Comparison Population and New York Farm Bureau Cohort Used in Analyses: 1973-1 979
Comparison population*
Total upstate New York Urbanized areas Other cities and towns with < 10 Farm Bureau addresses Remainder
Farm Bureau cohortt
n
%
n
2 903 788 - I 3aa 363
100.0 -47.8
20 a33 - I 041
100.0 - 5.0
- 767 697 747 128
- 26.5
- 981 18811
-4.9 90.3
25.7
%
Males, age 25 + y, 1980 U.S. census. t Males, age 18 + y.
MaylJune1990 [Vol. 45 (No. 3)l
157
Downloaded by [McGill University Library] at 07:34 12 January 2015
farm owners and operators. According to the 1980 U.S. Census,2o farm operators and managers made up .75% of employed males 16+ y of age in upstate New York. An additional 1.I% were farm workers or had related occupations. If we assume that all of these workers lived in the same towns as the Farm Bureau members, they then represented 2.9% and 4.2% of the population. Thus, at a maximum, 7.1% of the comparison population was engaged in an agricultural occupation. The study cohort was 2.5% of the comparison population and should have a minimal impact on standardized incidence ratios. The impact, in any case, would tend to be conservative, i.e., to reduce the difference between the study and the comparison groups. Farm workers’ experiences with cancer may be very different from operators and managers and so are appropriately included in the comparison group. Cancers among this comparison population were determined by searching the New York State Cancer Registry files from 1973 through 1983 for males 25+ y of age, with residence codes corresponding to those of the towns of interest.
Analysis. Person-years of observation for the study cohort by single years of age were computed as the difference between dates of entry and departure. The former equaled the date of first listing in the Farm Bureau membership rolls (beginning with January 1, 1973), whereas the latter was defined as date of death, date of cancer diagnosis, last date known alive before loss to follow-up, or the closing date of the study (December 31, 1983). The mid-year assumption of June 30 was used for persons with unknown months of entry or departure. If a Farm Bureau member developed a second primary malignancy during the study period, only the first tumor was included. Any member of the cohort whose registry record indicated that he had a previous cancer diagnosed before 1973 was excluded from the analysis. Overall and site-specific cancer incidence rates by single years of age were calculated for the comparison population. These rates were multiplied by the person-years of observation for each year of age to obtain the numbers of incident cancers expected for the farm owners and operators. The observed numbers of cancers in the study cohort were then divided by these expected numbers and multiplied by 100 to produce standardized cancer incidence ratios (SCIRS).~’For all cancer sites combined, SClRs were calculated for each of 10 age categories, beginning with 30-34 y and concluding with 75+ y. Small numbers precluded the computation of SClRs for men under 30 y of age and, in the analysis of site-specific incidence, necessitated that age be collapsed into two to five categories depending upon the degree of site specificity. Cancer sites were coded using the three-digit International Classification of Diseases, 9th Revision.= Using a Poisson model, a SClR was considered to be statistically significant at a probability value of .025 or less.= 158
ResuIts
Table 3 summarizes the follow-up status of the cohort. The number of men known to be alive through 1983 was 15 925 (84.9%), with approximately equal numbers ascertained through the Department of Motor Vehicles records and recent Farm Bureau membership lists. Once a person was identified with a primary cancer he was no longer followed. Deaths numbered 1 121 (6.0%), and 1 108 farm owners and operators (5.9%)were lost to follow-up. Ninety percent of the loss to follow-up occurred in men 30+ y of age. The number of person-years of observation for each 5-y age stratum, observed and expected numbers of cancers (all sites combined), and SClRs are given in Table4. The results generally indicated a deficit of incident cancers among the farm owners and operators, i.e., the SClRs varied from a minimum of 62.2 (p
Archives of Environmental Health: An International Journal Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/vzeh20
A Retrospective Cohort Study of Cancer Incidence among New York State Farm Bureau Members a
a
a
Dr. Alice D. Stark P.H , Hwa-Gan Chang M.S , Edward F. Fitzgerald Ph.D. , Karen Riccardi a
Ph.D. & Robert R. Stone Ph.D.
a
a
Bureau of Environmental and Occupational Epidemiology, New York State Department of Health , Albany, New York, USA Published online: 03 Aug 2010.
To cite this article: Dr. Alice D. Stark P.H , Hwa-Gan Chang M.S , Edward F. Fitzgerald Ph.D. , Karen Riccardi Ph.D. & Robert R. Stone Ph.D. (1990) A Retrospective Cohort Study of Cancer Incidence among New York State Farm Bureau Members, Archives of Environmental Health: An International Journal, 45:3, 155-162, DOI: 10.1080/00039896.1990.9936709 To link to this article: http://dx.doi.org/10.1080/00039896.1990.9936709
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
A Retrospective Cohort Study of Cancer Incidence among
Downloaded by [McGill University Library] at 07:34 12 January 2015
New York State Farm Bureau Members
ALICE D. STARK, Dr. P.H. HWA-GAN CHANC, M.S. EDWARD F. FITZGERALD, Ph.D. KAREN RICCARDI, B.S. ROBERT R. STONE, Ph.D. Bureau of Environmental and Occupational Epidemiology New York State Department of Health Albany, New York
ABSTRACT. Cancer incidence from 1973 through 1983 in 18 811 New York Farm Bureau members was examined using a retrospective cohort study design. The observed number of cancers for all age groups was 72% of the expected, and the major deficits in incidence occurred for lung (52% of expected), gastrointestinal (67%of expected), and bladder (78% of expected). Similar deficits have been reported by other researchers. Unlike other studies, we did not find a significant excess of cancer of any site. Given the healthy worker effect and the small numbers of incident tumors at some sites, the Standardized Cancer Incidence Ratios that were over 100 in value (i.e., lip, melanoma of the skin, prostate, multiple rnyeloma) merit further investigation. This study differs from previous research in population, setting, and method. Nonetheless, the general pattern of results is consistent with the findings of other investigations.
DESPITE a low overall cancer mortality rate, some investigators have found that farmers have disproportionately more deaths from certain tumors, e.g., prostate,’ skin,b non-Hodgkin’s lymphoma,’, and The results have led to the speculation that pesticides, zoonotic viruses, and other potentially carcinogenic exposures may be involved.ll Burmeister et al.4 found an increased odds ratio for leukemia in Iowa farmers in counties with the greatest numbers of egg-laying chickens and the largest number of acres treated with herbicides. Donham et al.3 also studied leukemia in Iowa and noted a highly positive correlation between acute lymphoid leukemia in males and cattle density. The relationship was greater for dairy cattle than for beef cattle. Mortality from non-Hodgkin’s lymphoma’ was MaylJune1990 [Vol. 45 (No.3)]
increased among farmers in Wisconsin (U.S.A.), especially in counties with high summary measures of general agricultural activity, small-grain acreage, wheat acreage, and acres treated with insecticides. A recent report by Reif et a1.,l0 which evaluated occupational risks for brain cancer, identified an increased risk among farmers; the highest risk was found for livestock farmers. Relatively few studies have examined these issues from the perspective of cancer incidence, and they have emphasized malignancies of the hematopoietic and nervous tiss u e ~ . ~Hoar , ~ ~et, a1.12 ~ ~ studied soft-tissue sarcoma, Hodgkins disease, and non-Hodgkin’s lymphoma in Kansas. Farm use of phenoxyherbicides was associated with nonHodgkin‘s lymphoma; frequent use increased risk. Neither soft-tissue sarcoma nor 155
Downloaded by [McGill University Library] at 07:34 12 January 2015
Hodgkin’s disease was associated with pesticide exposure. Pearce et aI.l3 did not find an association between non-Hodgkin’s lymphoma and exposure to phenoyxherbicides or chlorophenols. However, fencing work that necessitated exposure to risk factors, including arsenic and sodium pentachlorophenate, increased risk, as did employment in a meat works. The postulated risk factors in the meat works were 2, 4, 6-trichlorophenol and zoonotic viruses. There was significant interaction between the risks associated with these two activities. An Italian study8 of brain gliomas identified an increased risk for farmers. The increase in risk was attributable to use of insecticides and fungicides. Many farmers who were exposed to fungicides reported using commercial compounds of copper sulfate, some of which contained methyl urea, which has produced cancers of the nervous system in animals. The current study differed from previous research in that it focused on New York State, included only farm owners and operators, and utilized a retrospective cohort design to examine cancer incidence from 1973 through 1983. It followed the format of a previous report,14which examined overall mortality in the same cohort. Farming in New York State. According to the United States Census of Agriculture, there were 49 273 farms in New York State in 1978,15and the average size of each was 201 acres. Of these farms, 89% were individual or family operations, and 2% were incorporated. Reflecting this is the fact that in 1978, 65% of the state’s agricultural labor force consisted of family members who worked an average of 50 h/ wk.16 The average age of the farm operator was 50 y, and 94% percent were male. Ninety percent of these operators resided on their farms. New York State farms sold $2.19 billion worth of commodities in 1979. Dairy products accounted for 57.1%, fruit crops 8.3%, field crops 7.8%, vegetables 7.4%, and greenhouse and nursery products 4.6%. Materials and methods Study cohort. The study cohort was identified from the membership lists of the New York Farm Bureau obtained for 1973 through 1979. The Farm Bureau is a voluntary organization that was established in 1910. It represents the economic and political interests of farmers in New York State and provides group insurance plans, discount purchases of equipment, and other benefits. In 1973, the Farm Bureau had 11 627 regular members, and by 1979, the number had grown to 17 717. All farm owners and operators in New York State whose gross annual sales are at least $10 000 are eligible for membership; approximately 73% of this number belong to the Farm Bureau, using the 1978 United States Census of Agriculture data as the den0minat0r.l~The New York Farm Bureau’s philosophy is that members be active farmers and that the proportion of associate (nonfarmer) members be kept under 10%. Associate members were excluded from this study. 156
Fewer than 1% of the farmer members are not engaged in full-time physical labor on their farms (personal communication, New York Farm Bureau). Because the number of members who were female or who were less than 18 y of age was so low, these members were omitted from the study cohort. Persons who discontinued membership during the study period, however, were included under the assumption that even if they were no longer farming, exposures that they had incurred as farmers could affect their cancer experience. The result was a cohort of 20 833 males who were at least 18 y of age and who had been Farm Bureau members for at least 1 y during 1973-1979. Fifty-eight percent of the cohort had been members for all 7 y. Turnover resulting from dropouts was not a major problem, but increasing enrollment in the Farm Bureau over time reduced the average length of membership, i.e., 85% of the cohort was listed in 1979, compared with only 60% in 1973. Farmers also occasionally failed to renew membership in a given year but were reinstated subsequently, which resulted in a total duration of less than 7 y. Table 1 shows the age distribution of this cohort (mean = 44 y) at time of entry into the study, When comparing data from the 1978 United States Census of Agriculture to the study group, the study participants were relatively young.15 For example, 2.2% of census-designated farm operators in New York were less than 25 y of age v. 8.3% of the Farm Bureau cohort. Conversely, 19.2% of farm operators in the census were 65 y of age or older, compared with 8.5% for those in the current investigation. Data obtained from the membership lists included name, address, and type of farm. The number of years of membership was not available, and it was not possible to examine membership lists prior to 1973 because they were neither computerized nor centrally accessible. We could not, therefore, assess for each person the duration of his employment as a farmer. According to the Farm Bureau, however, their members have engaged in farming for a median period of at least 20 y (personal communication, New York Farm Bureau). Several methods were used to follow the cohort from 1973 through 1983 and to determine cancer incidence. A computer search of New York State Department of Motor Vehicles files for the last year of application or renewal for operator licenses and registrations was conducted. This procedure identified the most recent year that a participant was a resident of New York State and his date of birth. Once birthdates were obtained, deceased members of the study cohort were identified by computer matching with the New York State Bureau of Health Statistics death certificate files for 1973 through 1983. Definite matches required the agreement of name, county of residence, and birthdate ( 2 1 y). We were able to use strict criteria because of the reliability of the sources used for cohort identification. A final computer search matched the farmer cohort with New York State Cancer Registry files to Archives of EnvironmentalHealth
Table 1 .-Number ( n ) and percentage (%) of New York Farm Bureau Cohort, by Age at Entry into Study: 1973-1 979
Age fy)
n
1 729 4 295 4 604 4 959 3 485 1 345 41 6 20 a33
Downloaded by [McGill University Library] at 07:34 12 January 2015
18-24 25-34 345-54 55-64 65-74 75 + Total
%
8.3 20.6 22.1 23.8 16.7 6.5 2.0 100.0
identify cohort members who had been diagnosed with cancer. Because it was important to ascertain cancers in the study and comparison populations in an identical manner, only cases identified through the Cancer Registry were counted. The registry has been in existence since 1940 and includes all cases of cancer, excluding nonmelanoma skin cancer. It is more than 95% complete17for upstate New York, exclusive of New York City. The Cancer Registry and the death certificate files are periodically crossmatched to insure completeness of both databases. The matching rules for cancer were the same as for deaths. Tumor site, date of and age at diagnosis, stage, and histology were abstracted. To update the status of persons not found to be deceased, Farm Bureau membership lists were searched in reverse chronological order from 1980 through 1984 or to the most recent year in Motor Vehicles records. Comparison population. The comparison group potentially consisted of the 2 903 788 men who were at least 25 y of age who resided in New York State, exclusive of New York City, as enumerated by the 1980 U.S. census. The minimum age was 25 instead of 18 to allow for the 7-y difference between the first date of entry into the study and the date of the census. We first excluded from the comparison population the 47.8% who lived in towns that had at least two-
thirds of their area designated as urban. The reason for this exclusion was to avoid confounding any farmer-cancer incidence associations with urbanrural differences. For consistency, we also excluded from the study the 5.0% of Farm Bureau members who had an urban mailing address. Some approximations were necessary in using the 1981 National Zip Code Directory18and the 1980 Gazetteer of New York Statelgto identify towns of residence from the mailing addresses on the Farm Bureau membership lists. (The town was the smallest geographic unit studied because the accuracy of the residential information noted on vital records i s limited for smaller areas. Note that the entire area of New York State i s divided into towns. Towns reflect a geographic rather than a population density designation and may, in fact, be rural in nature.) If an owner or operator's zip code referred to a village, the entire town of which the village was a part was eligible for the comparison population. For villages divided between two towns, the first town listed in the Gazetteer was assumed to be where the farmer lived. If a mailing address for a farm owner or operator referred to a name for which there was both a town and a city, only the town was eligible for inclusion. If a town did not have or share a post office, it could not be eligible for the comparison population. In addition, another 26.5% who lived in towns with 10 or fewer Farm Bureau members were eliminated from the comparison population. This was done because the objective of this study was to compare the cancer experience of'farm owners and operators with that of men who resided in the same towns as the farmers, thereby isolating the effects of occupational exposures from more general environmental influences. Because these towns had proportionately very few farmers, they were not representative of the communities in which the farmers lived. The 4.9% of the Farm Bureau members with mailing addresses in these towns were similarly deleted. The net effect was to eliminate urbanized areas and rural towns without Farm Bureau members. As noted in Table 2, the result was a comparison population of 747 128 men and a study cohort for analysis of 18 811
Table 2.-Construction of Comparison Population and New York Farm Bureau Cohort Used in Analyses: 1973-1 979
Comparison population*
Total upstate New York Urbanized areas Other cities and towns with < 10 Farm Bureau addresses Remainder
Farm Bureau cohortt
n
%
n
2 903 788 - I 3aa 363
100.0 -47.8
20 a33 - I 041
100.0 - 5.0
- 767 697 747 128
- 26.5
- 981 18811
-4.9 90.3
25.7
%
Males, age 25 + y, 1980 U.S. census. t Males, age 18 + y.
MaylJune1990 [Vol. 45 (No. 3)l
157
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farm owners and operators. According to the 1980 U.S. Census,2o farm operators and managers made up .75% of employed males 16+ y of age in upstate New York. An additional 1.I% were farm workers or had related occupations. If we assume that all of these workers lived in the same towns as the Farm Bureau members, they then represented 2.9% and 4.2% of the population. Thus, at a maximum, 7.1% of the comparison population was engaged in an agricultural occupation. The study cohort was 2.5% of the comparison population and should have a minimal impact on standardized incidence ratios. The impact, in any case, would tend to be conservative, i.e., to reduce the difference between the study and the comparison groups. Farm workers’ experiences with cancer may be very different from operators and managers and so are appropriately included in the comparison group. Cancers among this comparison population were determined by searching the New York State Cancer Registry files from 1973 through 1983 for males 25+ y of age, with residence codes corresponding to those of the towns of interest.
Analysis. Person-years of observation for the study cohort by single years of age were computed as the difference between dates of entry and departure. The former equaled the date of first listing in the Farm Bureau membership rolls (beginning with January 1, 1973), whereas the latter was defined as date of death, date of cancer diagnosis, last date known alive before loss to follow-up, or the closing date of the study (December 31, 1983). The mid-year assumption of June 30 was used for persons with unknown months of entry or departure. If a Farm Bureau member developed a second primary malignancy during the study period, only the first tumor was included. Any member of the cohort whose registry record indicated that he had a previous cancer diagnosed before 1973 was excluded from the analysis. Overall and site-specific cancer incidence rates by single years of age were calculated for the comparison population. These rates were multiplied by the person-years of observation for each year of age to obtain the numbers of incident cancers expected for the farm owners and operators. The observed numbers of cancers in the study cohort were then divided by these expected numbers and multiplied by 100 to produce standardized cancer incidence ratios (SCIRS).~’For all cancer sites combined, SClRs were calculated for each of 10 age categories, beginning with 30-34 y and concluding with 75+ y. Small numbers precluded the computation of SClRs for men under 30 y of age and, in the analysis of site-specific incidence, necessitated that age be collapsed into two to five categories depending upon the degree of site specificity. Cancer sites were coded using the three-digit International Classification of Diseases, 9th Revision.= Using a Poisson model, a SClR was considered to be statistically significant at a probability value of .025 or less.= 158
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Table 3 summarizes the follow-up status of the cohort. The number of men known to be alive through 1983 was 15 925 (84.9%), with approximately equal numbers ascertained through the Department of Motor Vehicles records and recent Farm Bureau membership lists. Once a person was identified with a primary cancer he was no longer followed. Deaths numbered 1 121 (6.0%), and 1 108 farm owners and operators (5.9%)were lost to follow-up. Ninety percent of the loss to follow-up occurred in men 30+ y of age. The number of person-years of observation for each 5-y age stratum, observed and expected numbers of cancers (all sites combined), and SClRs are given in Table4. The results generally indicated a deficit of incident cancers among the farm owners and operators, i.e., the SClRs varied from a minimum of 62.2 (p
