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Biomedical subjects

P A Stewart

Publications and source records attributed to P A Stewart.

At least 19 recordsLinked to original sources

Design characteristics that affect speed of information access and clarity of presentation in an electronic neuroanatomy atlas.

Functional Neuroanatomy, an interactive electronic neuroanatomical atlas, was designed for first year medical students. Medical students have much to learn in a limited time; therefore a major goal in the atlas design was that it facilitate rapid, accurate information retrieval. To assess this feature, we designed a testing scenario in which students who had never taken a neuroanatomy course were asked to complete two equivalent tests, one using the electronic atlas and one using a comparable hard copy atlas, in a limited period of time. The tests were too long to be completed in the time allotted, so test scores were measures of how quickly correct information could be retrieved from each source. Statistical analysis of the data showed that the tests were of equal difficulty and that accurate information retrieval was significantly faster using the electronic atlas when compared with the hard copy atlas (P < 0.0001). Post-test focus groups (n = 4) allowed us to infer that the following design features contributed to rapid information access: the number of structures in the database was limited to those that are relevant to a practicing physician; all of the program modules were presented in both text and image form on the index screen, which doubled as a site map; pages were layered electronically such that information was hidden until requested, structures available on each page were listed alphabetically and could be accessed by clicking on their name; and an illustrated glossary was provided and equipped with a search engine.

Humans↗

Comparison between color Doppler cineloop- and conventional spectral Doppler-derived maximum velocity and flow in the umbilical vein.

OBJECTIVE: To compare the umbilical venous flow velocity derived from color Doppler cineloop recordings with that derived from conventional spectral Doppler in normal pregnancies. METHOD: In 18 uncomplicated pregnancies between 19 and 39 weeks' gestation, color Doppler was used to find the maximum velocity in the cross-sectional vessel area of a free-floating loop of the umbilical vein. The maximum velocity was determined using the software tool HDI_Lab (Philips Medical Systems) after tracing the vessel area of interest. Conventional spectral Doppler was then used to determine the maximum velocity with the High-Q machine option. The cross-sectional area of the umbilical vein was determined using B-mode imaging and was subsequently used to determine the umbilical volume flow from both Doppler methods. Assuming a parabolic flow profile in the umbilical vein, the mean velocity is equal to half the maximum velocity. The fetal weight was estimated from fetal biometry using the four-parameter Hadlock formula. RESULTS: Maximum velocity was significantly (P = 0.003) higher with color Doppler cineloop (14.3 +/- 2.5 cm/s) compared with spectral Doppler (12.7 +/- 3.2 cm/s). Therefore, using the same cross-sectional area for both methods, the umbilical blood flow was significantly higher (P = 0.001) with color Doppler cineloop (127.9 +/- 59.0 mL/min) than it was with spectral Doppler (112.8 +/- 54.1 mL/min). The umbilical blood flow expressed as volume flow per kg fetal weight was significantly (P = 0.01) higher with color Doppler cineloop (126.0 +/- 57.0 mL/min/kg) than it was with spectral Doppler (115.0 +/- 53.0 mL/min/kg). CONCLUSIONS: Umbilical venous flow velocity derived from color Doppler cineloops is approximately 10% higher than that derived from spectral Doppler-derived velocity. The reduced angle dependence of the color Doppler cineloop technique and the large sampling area of the cross-sectional vessel should allow better determination of the correct maximum velocity in the umbilical vein.

Blood Flow Velocity↗

Wall shear stress and related hemodynamic parameters in the fetal descending aorta derived from color Doppler velocity profiles.

This paper presents a methodology for estimating the wall shear stress in the fetal descending aorta from color Doppler velocity profiles obtained during the second half of pregnancy. The Womersley model was applied to determine the wall shear stress and related hemodynamic parameters. Our analysis indicates that the aortic diameter can be modeled as a function of the gestational age in weeks as: Diameter (mm) = 0.17.ga + 0.15 (R2 = 0.64, p < 0.001). The aortic volume flow showed a log linear gestational age-related increase that fit the model: F (mL/min) = e(0.08.ga + 3.49) (R2 = 0.61, p < 0.001). The Womersley number increased linearly with gestational age from 3.3 to 6.2 (p < 0.001) and the pressure gradient decreased linearly from 2.68 to 1.16 mPa/mm (p = 0.003) during the second half of pregnancy; the mean wall shear stress for the study group was 2.2 Pa (SD = 0.59) and was independent of gestational age. This study suggests that the size of the fetal aorta adapts to flow demands and maintains constant mean wall shear stress.

Aorta, Thoracic↗

Occupation and the risk of adult glioma in the United States.

OBJECTIVE: Previous studies have observed increased glioma incidence associated with employment in the petroleum and electrical industries, and in farming. Several other occupations have also been associated with increased risk, but with inconsistent results. We evaluated associations between occupational title and glioma incidence in adults. METHODS: Cases were 489 patients with glioma diagnosed from 1994 to 1998 at three United States hospitals. Controls were 799 patients admitted to the same hospitals for non-malignant conditions. An experienced industrial hygienist grouped occupations that were expected to have similar tasks and exposures. The risk of adult glioma was evaluated for those subjects who ever worked in an occupational group for at least six months, those who worked longer than five years in the occupation, and those with more than ten years latency since starting work in the occupation. RESULTS: Several occupational groups were associated with increased glioma incidence for having ever worked in the occupation, including butchers and meat cutters (odds ratio [OR] = 2.4; 95% confidence limits [CL]: 1.0, 6.0), computer programmers and analysts (OR = 2.0; 95% CL: 1.0, 3.8), electricians (OR = 1.8; 95% CL: 0.8, 4.1), general farmers and farmworkers (OR = 2.5; 95% CL: 1.4, 4.7), inspectors, checkers, examiners, graders, and testers (OR = 1.5; 95% CL: 0.8, 2.7), investigators, examiners, adjustors, and appraisers (OR = 1.7; 95% CL: 0.8, 3.7), physicians and physician assistants (OR = 2.4; 95% CL: 0.8, 7.2), and store managers (OR = 1.6; 95% CL: 0.8, 3.1), whereas occupation as a childcare worker was associated with decreased glioma incidence (OR = 0.4; 95% CL: 0.2, 0.9). These associations generally persisted when the subjects worked longer than five years in the occupation, and for those with more than ten years latency since starting to work in the occupation. CONCLUSIONS: This is our first analysis of occupation and will guide future exposure-specific assessments.

Adult↗

Two-dimensional and M-mode echocardiography of the fetal coronary sinus.

OBJECTIVE: To document fetal coronary sinus dimensions in normal pregnancy. METHODS: Two hundred and sixty-five normal fetuses in which congenital cardiac defects had been excluded were examined cross-sectionally between 21 and 38 weeks of gestation. From the apical or basal four-chamber view the transducer was tilted towards the inferior cardiac surface in order to visualize the coronary sinus by real-time ultrasound. Maximum systolic and diastolic diameters were measured using M-mode. Reference ranges were constructed and the ratio of systolic and diastolic diameters calculated. Data from two fetuses, one with supraventricular tachycardia and a second one with hydrops secondary to anemia, were also compared. RESULTS: Visualization and measurement of the coronary sinus were successful in 258 (97.4%) patients. The coronary sinus systolic and diastolic diameters increased significantly with gestational age (maximum systolic diameter, 1.6 mm at 21 weeks to 4 mm at 38 weeks; maximum diastolic diameter, 0.9 mm at 20 weeks to 2.2 mm at 38 weeks). The ratio of systolic to diastolic diameters remained relatively constant (range, 1.7-2.1) and therefore was unrelated to gestational age. In the fetuses with supraventricular tachycardia and hydrops, both diameters of the coronary sinus were increased and diminished fluctuation in size during the cardiac cycle was observed. CONCLUSIONS: The described sonographic approach provides an effective method for measurement of coronary sinus dimensions. The normative data may facilitate the detection of coronary sinus dilation as an indirect marker for abnormalities in venous return to the heart.

Diastole↗

A novel strategy for NQO1 (NAD(P)H:quinone oxidoreductase, EC 1.6.99.2) mediated therapy of bladder cancer based on the pharmacological properties of EO9.

The indolequinone EO9 demonstrated good preclinical activity but failed to show clinical efficacy against a range of tumours following intravenous drug administration. A significant factor in EO9's failure in the clinic has been attributed to its rapid pharmacokinetic elimination resulting in poor drug delivery to tumours. Intravesical administration of EO9 would circumvent the problem of drug delivery to tumours and the principal objective of this study is to determine whether or not bladder tumours have elevated levels of the enzyme NQO1 (NAD(P)H:quinone oxidoreductase) which plays a key role in activating EO9 under aerobic conditions. Elevated NQO1 levels in human bladder tumour tissue exist in a subset of patients as measured by both immunohistochemical and enzymatic assays. In a panel of human tumour cell lines, EO9 is selectively toxic towards NQO1 rich cell lines under aerobic conditions and potency can be enhanced by reducing extracellular pH. These studies suggest that a subset of bladder cancer patients exist whose tumours possess the appropriate biochemical machinery required to activate EO9. Administration of EO9 in an acidic vehicle could be employed to reduce possible systemic toxicity as any drug absorbed into the blood stream would become relatively inactive due to an increase in pH.

Antineoplastic Agents↗

Occupational exposure to pesticides and pancreatic cancer.

BACKGROUND: An increased risk of exposure to pesticides for pancreatic cancer has been suggested in a number of epidemiologic studies. METHODS: Cases (N = 484), aged 30-79 years, were diagnosed in 1986-1989. Controls (N = 2,095) were a random sample of the general population. Information on usual occupation and potential confounding factors was obtained. A job-exposure matrix (JEM) approach was used to estimate the level of occupational exposure to pesticides. RESULTS: A significant trend in risk with increasing exposure level of pesticides was observed, with ORs of 1.3 and 1.4 for low and moderate/high exposure levels, respectively. Excess risks were found for occupational exposure to fungicides (OR = 1.5) and herbicides (OR = 1.6) in the moderate/high level after adjustment for potential confounding factors. An increased risk for insecticide exposure was disappeared after adjustment for fungicide and herbicide exposures. Results of our occupation-based analysis were consistent with those from the JEM-based analysis. CONCLUSIONS: Our results suggest that pesticides may increase risk of pancreatic cancer, and indicate the need for investigations that can evaluate risk by specific chemical exposures. Published 2001 Wiley-Liss, Inc.

Adult↗

Occupation and leukemia: a population-based case-control study in Iowa and Minnesota.

BACKGROUND: Studies have suggested that risk of leukemia may be associated with occupational or industrial exposures and risk may vary by the histological type of the disease. METHODS: A population-based case-control study was conducted in Iowa and Minnesota to evaluate the association between various occupations, industries, and occupational exposures and leukemia risk. A total of 513 cases and 1,087 controls was included in the study. A lifetime occupational history and other risk factor information were collected through in-person interviews, and a job-exposure matrix was used to assess possible risks associated with specific exposures. RESULTS: A significantly increased risk of leukemia was observed among agricultural service industries and among nursing and healthcare workers. Janitors, cleaners, and light truck drivers also experienced increased risk. Those employed in plumbing, heating and air conditioning industries, and sales of nondurable goods (such as paints and varnishes) had an increased risk. Printers, painters, and workers in the food and metal industries had a nonsignificantly increased risk of leukemia. Analyses by specific exposures and histology of leukemia showed that risk of leukemia associated with occupational or industrial exposures may vary by histological type of the disease. CONCLUSIONS: An increased risk of leukemia among workers employed in agricultural industries, nursing and healthcare workers, and in a few occupations with possible exposure to solvents is consistent with earlier studies. Associations of risk with occupations not observed previously deserve further assessment. Published 2001 Wiley-Liss, Inc.

Adult↗

Determining the probability of pesticide exposures among migrant farmworkers: results from a feasibility study.

BACKGROUND: Migrant and seasonal farmworkers are exposed to pesticides through their work with crops and livestock. Because workers are usually unaware of the pesticides applied, specific pesticide exposures cannot be determined by interviews. We conducted a study to determine the feasibility of identifying probable pesticide exposures based on work histories. METHODS: The study included 162 farm workers in seven states. Interviewers obtained a lifetime work history including the crops, tasks, months, and locations worked. We investigated the availability of survey data on pesticide use for crops and livestock in the seven pilot states. Probabilities of use for pesticide types (herbicides, insecticides, fungicides, etc.) and specific chemicals were calculated from the available data for two farm workers. The work histories were chosen to illustrate how the quality of the pesticide use information varied across crops, states, and years. RESULTS: For most vegetable and fruit crops there were regional pesticide use data in the late 1970s, no data in the 1980s, and state-specific data every other year in the 1990s. Annual use surveys for cotton and potatoes began in the late 1980s. For a few crops, including asparagus, broccoli, lettuce, strawberries, plums, and Christmas trees, there were no federal data or data from the seven states before the 1990s. CONCLUSIONS: We conclude that identifying probable pesticide exposures is feasible in some locations. However, the lack of pesticide use data before the 1990s for many crops will limit the quality of historic exposure assessment for most workers.

Adolescent↗

A method for assessing occupational pesticide exposures of farmworkers.

BACKGROUND: The health of farmworkers as related to pesticide exposure is of concern but assessing exposures for epidemiologic studies requires different techniques than approaches used for studies of industrial workers. METHODS: A review of the literature identified possible factors that affect exposure intensity. A model was developed to estimate an exposure score. Exposures in the literature were estimated using the model and compared to the measurements in the literature. RESULTS: Three studies were found with information appropriate for evaluation of the model. There was a statistical difference between the means of the scores corresponding to above and below the median of the measurements. The correlation coefficient between the scores and the measurements from the literature was 0.77. CONCLUSIONS: Although the evaluation was limited, the model appeared to work well, but more testing is needed. More research is also needed to increase understanding of what affects the exposures of these workers.

Agriculture↗

Prenatal diagnosis of ventriculocoronary fistula.

BACKGROUND: Cardiac anomalies may be associated with abnormal coronary vascular connections. We report the prenatal diagnosis of ventriculocoronary fistula in three fetuses with associated cardiac anomalies. MATERIALS AND METHODS: Fetal echocardiography was performed in three patients referred for suspected cardiac anomaly. Two-dimensional fetal echocardiography was complemented by color Doppler flow imaging and spectral Doppler in all cases. RESULTS: A ventriculocoronary fistula was diagnosed in three patients referred at 22, 23 and 32 weeks. The first patient had hypoplastic left heart associated with transposition of the great arteries and pulmonary atresia with an intact interventricular septum. The coronary fistula arose from the transposed aorta to the left ventricle. In two patients ventriculocoronary fistula was found in association with pulmonary atresia and an intact interventricular septum. In all cases there was bidirectional flow within the fistula (diastolic blood flow towards the ventricle with reversal during ventricular systole). The pregnancy with hypoplastic left heart with transposition, and one of those with pulmonary atresia resulted in neonatal death and stillbirth, respectively. In the third instance the ventriculocoronary fistula was verified by postpartum cardiac angiography. The infant initially received a Blalock-Taussig shunt, subsequently replaced by a bidirectional Glenn shunt, and was doing well at the time of writing. CONCLUSION: A ventriculocoronary fistula can be identified prenatally by color and spectral Doppler. This anomaly should be sought in fetuses with outflow tract obstructive cardiac lesions and an intact interventricular septum. Prenatal diagnosis allows early angiography postnatally. Delineation of coronary vascular regions may therefore facilitate preoperative planning.

Adult↗

A pilot study to rate determinants of exposure from videotaped work activities of farmers' use of pesticides.

Industrial hygienists often observe workers to determine who should be measured based on a predicted exposure level. Such evaluations are usually based on real-time observation, yet surprisingly little research has been conducted on what determinants of exposure industrial hygienists use to rank workers and whether the ranking is accurate. Accuracy of the ranking may also be affected by the observation process, which is limited when conditions in the workers' immediate environment are rapidly changing. An alternative to real-time observation is videotaping workers and evaluating the tapes at a later date. A pilot study was conducted using previously collected data to determine if workers could be ranked by exposure level utilizing a scoring system to rate videotaped work practices. Six farmers had been videotaped and their dermal exposures measured as they applied insecticide to hogs. In this study, scores were developed to rate the farmers' working conditions by exposure level. Two types of determinants were used to describe exposure: touching and work practices. Touching included the number of times parts of the body had contact with surfaces possibly contaminated with insecticide. Work practices included the types of clothing and protective equipment worn as well as specific practices used by the farmer (e.g., application method). Two raters conducted independent assessments of the videotape using the same criteria. One rater reviewed the tape twice. Agreement between the raters for the "touching" score was weak (intra-class coefficient (ICC) = 0.28), but there was excellent agreement between the two raters (ICC = 0.92) for overall quality of work practices. As expected, a greater number of touches was moderately correlated with an increase in total exposure (rs = 0.60) and there was a weak inverse relationship between protective work practices and the exposure under the clothing (rs = -0.26). All other relationships with exposure level were contrary to what was expected. Since videotapes provide the industrial hygienist with a record of work events and can capture details that might otherwise be missed or not considered they may play a useful role in exposure assessment, especially if carefully developed procedures are followed to overcome the limitations found by this pilot study.

Agriculture↗

Endothelial vesicles in the blood-brain barrier: are they related to permeability?

1. Macromolecules cross capillary walls via large vascular pores that are thought to be formed by plasmalemmal vesicles. Early hypotheses suggested that vesicles transferred plasma constituents across the endothelial wall either by a "shuttle" mechanism or by fusing to form transient patent channels for diffusion. Recent evidence shows that the transcytotic pathway involves both movement of vesicles within the cell and a series of fusions and fissions of the vesicular and cellular membranes. 2. The transfer of macromolecules across the capillary wall is highly specific and is mediated by receptors incorporated into specific membrane domains. Therefore, despite their morphological similarity, endothelial vesicles from heterogeneous populations in which the predominant receptor proteins incorporated in their membranes define the functions of individual vesicles. 3. Blood-brain barrier capillaries have very low permeabilities to most hydrophilic molecules. Their low permeability to macromolecules has been presumed to be due to an inhibition of the transcytotic mechanism, resulting in a low density of endothelial vesicles. 4. A comparison of vesicular densities and protein permeabilities in a number of vascular beds shows only a very weak correlation, therefore vesicle numbers alone cannot be used to predict permeability to macromolecules. 5. Blood-brain barrier capillaries are fully capable of transcytosing specific proteins, for example, insulin and transferrin, although the details are still somewhat controversial. 6. It has recently been shown that the albumin binding protein gp60 (also known as albondin), which facilitates the transcytosis of native albumin in other vascular beds, is virtually absent in brain capillaries. 7. It seems likely that the low blood-brain barrier permeability to macromolecules may be due to a low level of expression of specific receptors, rather than to an inhibition of the transcytosis mechanism.

Animals↗

Early prenatal ultrasound diagnosis of cleidocranial dysplasia.

A woman was referred in the first trimester of her third pregnancy because of a family history of cleidocranial dysplasia. An ultrasound examination at 14 weeks 4 days revealed a fetus with appropriate biometric measurements. However, the clavicles were noted to be hypoplastic and the cranium appeared less well ossified than expected for gestational age, suggesting the diagnosis of cleidocranial dysplasia. On subsequent examination at 21 weeks, the findings were essentially unchanged. Induced vaginal delivery owing to decreased amniotic fluid volume occurred at 37 weeks, and a female weighing 3200 g was delivered. The infant had clinical and X-ray signs of cleidocranial dysplasia.

Adult↗

Occupational exposure to formaldehyde and wood dust and nasopharyngeal carcinoma.

OBJECTIVES: To investigate whether occupational exposures to formaldehyde and wood dust increase the risk of nasopharyngeal cancer (NPC). METHODS: A multicentered, population based case-control study was carried out at five cancer registries in the United States participating in the National Cancer Institute's SEER program. Cases (n=196) with a newly diagnosed NPC between 1987 and 1993, and controls (n=244) selected over the same period from the general population through random digit dialing participated in structured telephone interviews which inquired about suspected risk factors for the disease, including a lifetime history of occupational and chemical exposure. Histological type of cancer was abstracted from clinical records of the registries. Potential exposure to formaldehyde and wood dust was assessed on a job by job basis by experienced industrial hygienists who were blinded as to case or control status. RESULTS: For formaldehyde, after adjusting for cigarette use, race, and other risk factors, a trend of increasing risk of squamous and unspecified epithelial carcinomas was found for increasing duration (p=0.014) and cumulative exposure (p=0.033) but not for maximum exposure concentration. The odds ratio (OR) for people cumulatively exposed to >1.10 ppm-years was 3.0 (95% confidence interval (95% CI) 1.3 to 6.6) compared with those considered unexposed. In analyses limited to jobs considered definitely exposed, these trends became stronger. The associations were most evident among cigarette smokers. By contrast, there was no association between potential exposure to formaldehyde and undifferentiated and non-keratinising carcinomas. There was little evidence that exposure to wood dust increased risk of NPC, as modest crude associations essentially disappeared after control for potential exposure to formaldehyde. CONCLUSIONS: These results support the hypothesis that occupational exposure to formaldehyde, but not wood dust, increases risk of NPC. This association seems to be specific to squamous cell carcinomas. Established cohorts of workers exposed to formaldehyde and wood dust should continue to be monitored for NPC and other respiratory cancers. Future studies of NPC should take into account histological type in assessing risk from environmental and host factors.

Adolescent↗

Comparison of industrial hygienists' exposure evaluations for an epidemiologic study.

OBJECTIVES: A study was conducted to determine what level of information is required by industrial hygienists before they can develop exposure estimates comparable with those developed from a more in-depth evaluation. METHODS: Three industrial hygienists evaluated formaldehyde exposures of 300 jobs selected from an earlier epidemiologic study. The jobs were evaluated over the following 6 cycles: (i) job title and industry; (ii) job title, industry, dates; (iii) job and department title and industry; (iv) cycle 3 information with dates; (v) cycle 3 information with a plant report; and (vi) job and department title, industry, dates, and the report. Each hygienist assigned jobs to 1 of 4 exposure categories, which were compared with the categories in the original epidemiologic study. RESULTS: Overall, the mean differences between the hygienists' evaluations and the standard, although small, changed little over the cycles. The kappa statistic was poor to moderate for all the cycles, but the agreement was greater than expected due to chance. There was moderate improvement in overall agreement over the cycles using the weighted kappa statistic, but little improvement in the intraclass correlation coefficients of the hygienists' evaluations, which ranged from 0.4 to 0.5. Department information improved the agreement with the standard by 5--10%, but dates did not the improve agreement. There were some differences by type of plant, job function, exposure level, and date of the estimate. Using a hypothetical exposure-response scenario, this level of misclassification would have resulted in missing an association. CONCLUSIONS: Although there was slight improvement with increasing levels of information, these findings suggest that the subjective categorical assessment of exposures by industrial hygienists will not produce exposure estimates comparable to more in-depth evaluations of exposure.

Epidemiologic Methods↗

Exposure of farmers to phosmet, a swine insecticide.

OBJECTIVES: The goal of this study was to measure dermal and inhalation exposures to phosmet during application to animals and to identify what determinants of exposure influence the exposure levels. METHODS: Ten farmers were monitored using dermal patches, gloves, and air sampling media during normal activities of applying phosmet to pigs for insect control. Exposures were measured on the clothing (outer), under the clothing (inner), on the hands, and in the air. Possible exposure determinants were identified, and a questionnaire on work practices was administered. RESULTS: The geometric mean of the outer exposure measurements was 79 microg/h, whereas the geometric mean of the inner exposure measurements was 6 microg/h. The geometric mean for hand exposure was 534 microg/h, and the mean air concentration was 0.2 microg/m3. Glove use was associated with the hand and total dermal exposure levels, but no other determinant was associated with any of the exposure measures. The average penetration through the clothing was 54%, which dropped to 8% when the farmers wearing short sleeves were excluded. The farmers reported an average of 40 hours a year performing insecticide-related tasks. CONCLUSIONS: Farmers who applied phosmet to animals had measurable exposures, but the levels were lower than what has been seen in other pesticide applications. Inhalation exposures were insignificant when compared with dermal exposures, which came primarily from the hands. Clothing, particularly gloves, provided substantial protection from exposures. No other exposure determinant was identified.

Animal Husbandry↗

The impact of initial job assignment on formaldehyde exposure among African-American and white formaldehyde industry workers.

We compared initial job assignments of African-American and white employees at eight worksites that used formaldehyde between 1940 and 1979. Unexposed workers were excluded. Median, ambient air formaldehyde, 8-hour, time-weighted average (TWA8) exposure estimates were determined for each worksite. Job assignments with TWAs above the worksite's median TWA8 were called high formaldehyde exposed (HFE). Job assignments with TWAs less than or equal to the worksite's median TWA8 for the same period were called lower formaldehyde exposed (LFE). Two worksites assigned black workers to HFE jobs in significantly higher proportions than white workers in some decades. One worksite assigned white workers in significantly higher proportions than black workers to HFE jobs in some decades. One worksite assigned racial groups in nearly equal proportions from 1940 to 1969. The remaining sites showed insignificant assignment disproportions (alpha = 0.05; Chi-square < or = 3.841, 1 degree of freedom) for any period. No major trend was apparent across all plants and decades.

Black or African American↗