Document BymQzDDwryEv8jaEGaKKwxGmJ

9-10-71 i MGOtt PLAINTIFF'S EXHIBIT STATISTICAL EVALUATION OF RESPIRATORY SYSTEM INDICATORS AMONG INSULATORS DOW COMRDEIntroduction This report presents statistical findings developed from an epidemiologic study of insulators employed by the Texas Division of The Dow Chemical Company. The report does not include a literature review or a medical interpretation of the results. These crucial elements of a study are properly left to the industrial physician responsible for the health of these workers. The objectives of the statistical evaluation were: (1) to identify through per sonnel records all employees who worked as insulators at the Texas Division; (2) to determine the current status of these workers and the dates of their em ployment as insulators; and, (3) to examine the relationship between exposure CD CD CD cn cn CD UD duration and several respiratory system indicators, namely the number of morbidity episodes due to diseases of the respiratory system, the number of deaths due to respiratory cancer and two respiratory function measures, the forced midexpiratory flow (FEF25_75) and the forced expiratory volume at three seconds (FEV^). The insulator craft has existed since 1941 at the Texas Division. Between 1941 and 1971, seventy-two men who worked as insulators were identified through per sonnel lists. As of August 1971, the status of these workers was as follows: Total--------------------------------------------------------- 72 Still Working For Texas Division Active Insulators ---------------- 29 Not Active As Insulators - 1 30 Released From Company---------------------- 29 Retired --------------------------------------------------- 9 Transferred From Texas Div. --------Deceased ------------------------------------------------ 2 2 411394 Two factors which pose limitations on the statistical analysis are evident from the above tabulation. These factors are: (1) the rather small size of the exposed to risk population (72 men), and, (2) the large percent of these employees released from emolo'-mer.t (4D"). I- Methodology Seniority lists for the insulator craft which were available through the Personnel Department were reviewed to identify the population-at-risk. Since insulators participated in the periodic health exam program, a double check of the population was possible. The verification procedure revealed that the seniority lists had provided complete and accurate identification of the population. The work history 00990001S card for each in-scope employee was examined to determine the date of birth, the current status of the employee, and the dates during which the employee worked as an insulator. Years-on-job was subsequently used as an indicator of relative expo sure levels. Morbidity Data Morbidity episodes are recorded in the employee's medical record. The date of the episode and the physician's diagnosis are listed for each event. Extracting this information was most time consuming because of the need to pull individual records and the unedited nature of the data. Since no prior use of these data for statistical purposes is known to the author, it was necessary to assume that the completeness of reporting and quality of the information was adequate. Morbidity data for the exposed-to-risk population were abstracted beginning in 1960. The number of episodes by cause and the frequency of episodes per 100 work-years-at-risk were tabulated for the total insulator population. A matched pairs design was used to compare the mor bidity experience of the insulators with that of a suitable control group. In this case, the control group was selected from Power Department employees. Resources were conserved by restricting the comparison to the 24 insulators who worked con tinuously from 1960 through July 1971 versus 24 Power Department employees of the same age. These employees also worked continuously during the observation period. The pairing procedure eliminated the need to take into account the age of the worker or the period of observation in comparisons between the two groups. Until such time CD 00 that routine data processing of morbidity data is initiated, the matched pairs type "d- of analysis will remain the most efficient way to statistically treat morbidity data. ST0 0 0 6 6 0 1 -3- Spirometric Measurements Spiromecric measurements for insulators were provided through the periodic health exam program. The most recent testing for each insulator was selected for analysis. Readings were available for 42 insulators. Two measures, the FEF25_75% and the FEV^, were selected for analysis. The age and height, as well as smoking history, were obtained for each insulator at the time of his exam. Because of several limitations, three categories--nonsmoker, current smokers of at least one pack per day, and all others,--were used to describe the smoking history for each worker. The objective of this phase of the study was to determine if the two respiratory function measures, corrected for age, height and smoking history, were related to years-on-job. Age and height corrections for the FIV3 were based on "Guides To The Evaluation of Permanent Impairment - The Respiratory System" (1965). A factor of .95 was used to adjust FVC readings to FEV3 readings. Age and height corrections for the FEF25_75y were obtained from "Spirometric Standards For Healthy Nonsmoking Adults" by Morris, et al (1971). The ^^^25-75% readings were dichotomized according to the sign of the deviations from predicted norms to simplify the analysis. Mortality Data The mortality analysis was based on copies of death certificates received by the Company Group Insurance Department as proof of death. Individuals released from the Company, excluding retirees, are lost to any mortality study based strictly on insurance records. The potential biases introduced by this loss of information have been discussed in the literature. The control group for the mortality com parisons consisted of a cohort of 6500 Midland location hourly workers followed between 1954 and 1969. The expected numbers of deaths were calculated based on mortality rates for the cohort population, adjusting for age by the indirect method. 411396 -4- ST0 0 0 G602 Results Morbidity Analysis The overall morbidity experience for insulators from 1960 to August 1971 is sum marized in Table 1. As expected, episodes related to diseases of the respiratory system account for over forty percent of the total absences due to sickness. Table 2 shows a comparison of morbidity experience between insulators and Power Department employees. The between individual range in the number of total episodes (0 to 20) indicates the wide variability in utilization of group insurance benefits. There are no statistically significant differences at the .05 level between the two groups. This is true both with respect to total episodes and with respect to episodes due to diseases of the respiratory system. Spirometric Analysis Table 3 shows the average deviations of FEV3 readings from predicted norms by years of exposure. No significant association at the .05 level was found between years of exposure and FEV3. Adjustments for smoking history had little effect on the re sults. The scatter plot of individual FEV3 deviations from predicted versus yearson-job is shown in Figure I. In contrast. Table 5 indicates that nonsmokers perform near predicted norms and about .4 liters better than the average of either of the two smoking groups. Similar results are obtained for the percent of FEF25-75% readings below predicted norms. Thus, smoking history was found to be related to respiratory function performance while years on the job was not. The possible effects on these readings of selection biases, such as population attrition, are unknown. Mortality Analysis Table 6 summarizes the mortality findings of the study. The observed deaths among insulators is less than expected in each category of comparison. However, since the exposed-co-risk population is relatively small and the period of observation is short, the favorable experience to date does not, in itself, insure similar results in the future. 411397 ST0006603 -5- SlITTlTBarV The statistical evaluation was carried out along the lines set forth in the Introduction of this report. While the necessary data were indeed available, they were sometimes a burden to gather. This was especially true when they had been microfilmed. With regard to the insulators, no evidence was found to indicate an association between years on the job and the respiratory system indicators which were investigated. The many qualification statements which appeared in the report attest to the fact that the data were collected under real world and not laboratory conditions. 411398 ST0006604 Table 1. Episodes Of Morbidity Observed Since 1960 Among 46 Insulators Actively Employed As Of 1960. Cause Number Of Enisodes All Causes 166 Diseases of the Respiratory System 70 Accidental Injuries 20 Diseases of the Digestive System 18 Diseases of the Circulatory System 14 Diseases of the Genito-Urinary System 14 Diseases of the Nervous System and Sense Organs 8 Infective & Parasitic Diseases 7 Diseases of the Musculoskeletal System & Connective Tissue Neoplasms - Total l 7 4 Endocrine, Nutritional & Metabolic Diseases Mental Disorders , 1 ! -- -- Diseases of the Skin & Subcutaneous Tissue All Other Causes ! 1 ; i 1 i -- 4 Number Of Episodes Per 100 Person Years At Risk 39.1 16.5 4.7 4.2 3.3 3.3 1.9 1.7 1.7 .9 -- -- -- .9 411399 I- ST0006605 Table 2. Comparison Of Morbidity Episodes Occurring Between January 1960 And July 1971 For 24 Insulators Paired With 24 Power Department Employees Based On Age. Pair Number 1 Total Episodes I Insulators ; Power Dept.Emol. 2! ! Respiratory Episodes Insulators Power Dept.Emol. 0 10 2 ! 01 7 3 i 1 8 1 j 0 4 !5 1 5 !3 6 4 6 |3 1 7 i6 i 8 j2 20 2 5 0 i1 5 0 0i l i 21 i 3 l 1j 4 0 1 0 8 1 3 9 75 10 1' 2 11 ! 4 l 12 : 6 0 4 3 13 : 2 14 : 2 5 0 15 ! l 1 16 3 4 17 6 ' 18 1 10 19 11 1 20 6 21 8 12 7 5 i 2 22 3 23 6 1 24 4 5 2 6 Total 110 123 Number cf Epi 40.0 44.2 soceS'100 Per -,cn Years At Risk 5 i 2j 3! 3 0 0 2! 1! i !1 1 1i jI ! 0! j1 11 0 0 0 0 1 1; 1 7; 8 2 2i 4 i 1 3I i 0 5 i 1 1i i 3 1 1 13 49 17.6 51 18.4 411 S T0006606 Table 3. Mean FEV, Readings Expressed As Deviations From Predicted Norms By Exposure Group, Adjusted And Unadjusted For Smoking History. Exnosure Grout) < 10 Years 10 - 19 Years 20 - 29 Years Average Exposure Years 3.1 16.1 24.5 Number of Men 8 17 17 FEV3 In Liters Adjusted For I Unadjusted For Smoking History 1 Smoking Historv -.13 -.28 -.19 -.13 -.34 -.14 ___________________________ ! Table 4. Percent Of ^^25-157. Readings Below Predicted Norm By Exposure Group, Adjusted And Unadjusted For Smoking History. Exposure Group < 10 Years 10 - 19 Years 20 - 29 Years - Average Exposure Years 3.1 16.1 24.5 Number of Men 8 17 17 % Of FEF25_75% Below Predicted Norm Adjusted For Smoking Historv Unadjusted For Smoking Historv 38 38 42 47 38 35 Table 5. Mean FEV-j Readings Expressed As Deviations From Predicted Norms And Percent Of FEF23_75 Readings Below Predicted Norm By Smoking Category. Smoking Category Nonsmokers Current Smokers Of At Least One Pack Per Day All Other Number of Men 10 13 19 Deviations Of FEV^ In Liters From Pre dicted Norms +.09 % Of FEF25_75% Below Predicted Norms 10 -.32 -.31 46 53 411401 Table 6. Observed And Expected Deaths Among Insulators By Interval Since First Exposure Interval Since First Exposure Total Less Than 20 Years More Than 20 Years Years Exposed To Risk 942.1 806.2 135.9 Total Deaths Observed Expected 2 4.4 2 2.7 0 1.7 Deaths Due To Respiratory Cancer Observed I Expected 0 .3 0 .2 0 .1 ST0006607 411402 ST0006608 I FIGURE I. SCATTER PLOT OF DEVIATIONS IN FEV3 FROM PREDICTED VERSUS YEARS ON JOB FOR 42 INSULATORS (ADJUSTED FOR SMOKING HISTORY) 1 i 0 1I '+ lb YEARS ON JOB 411403 60990001S FIGURE I SCATTER PLOT OF DEVIATIONS IN FEV3 FROM PREDICTED VERSUS YEARS ON JOB FOR 42 INSULATORS (ADJUSTED FOR SMOKING HISTORY) O ----- .H * - -**- ------ " ' ; ' _ ---- ---------:--; _ V . "" --*------ -- ------------v 1 * ---------------- is- 14- lb YEARS ON JOB 411404