California Seventh-Day Adventists Research Articles

Parity and total, ischemic heart disease and stroke mortality. The Adventist Health Study, 1976–1988

In a prospective study with information about life style and reproductive factors, we assessed the relationship between parity and total, ischemic heart disease, and stroke mortality. The large majority of the 19,688 California Seventh-day Adventist women included did not smoke or drink alcohol, 31 percent never ate meat and physical activity was relatively high. Cox proportional hazard analysis was conducted with parity as the main independent variable and with adjustment for a number of other possible confounders. During follow-up from 1976 through 1988, there were 3,122 deaths; 782 deaths from ischemic heart disease and 367 deaths due to stroke. There were no relationships between parity and total mortality (P-value for overall effect of parity = 0.32). Grand multiparous women (>4 children) had somewhat increased ischemic heart disease mortality (MRR = 1.45, 95% CI: 1.15, 1.84) before adjustment for educational level. After adjustment for educational level and marital status, there were no relationship with mortality from ischemic heart disease (P = 0.29) or stroke (P = 0.72). In parous women, there were, after adjustment for age at first delivery, some suggestions of an increased total mortality in women with one child. For ischemic heart disease and stroke mortality, no associations were found. Stratified and adjusted analyses confirmed these results. Thus, we found no consistent relationships between parity and total, ischemic heart disease or stroke mortality. However, a longer follow-up would have been helpful and the conclusions may be somewhat influenced by the lifestyle of the women included.

Dietary Risk Factors for Ovarian Cancer: The Adventist Health Study (United States)

Few prospective studies have reported dietary risk factors for ovarian cancer. A total of 71 histologically confirmed epithelial ovarian cancers occurred among 13,281 non-Hispanic white California Seventh-day Adventist women during follow-up. Participants were part of the Adventist Health Study (AHS) and had no history of cancer or hysterectomy at baseline in 1976 when they completed a detailed lifestyle questionnaire including a dietary assessment. The association of dietary variables with either all ovarian cancer cases or postmenopausal cases was tested using proportional hazards regression with adjustment for age and other covariates. The strongest hazardous risk factor associations among the food variables were found for meat intake with a risk ratio (RR) of 2.42 for intake > or = 1 time/week versus no meat (p for trend = 0.006), and cheese intake with a RR of 2.02 for intake of > 2 time/week versus < 1 per week (p for trend = 0.10), both of these being in postmenopausal cases. We found significantly reduced risk of all ovarian cancer with higher tomato consumption (RR = 0.32) comparing intakes > or = five times/week versus never to < 1 time/week (p for trend = 0.002), and also with higher fruit consumption (p < 0.01). A weak protective association was found with low fat, but not whole milk. Little confounding was observed between these foods.

Correlations between Estimated and True Dietary Intakes: Using Two Instrumental Variables

We describe a new application of the method of triads that allows an estimate of the correlation between a dietary questionnaire measure (Q) and true intake (T). Three surrogate variables Q, M, and P are observed where M and P are both instrumental (often biological) variables. A reference dietary method (R) is not required. The variables M and P may be concentration rather than recovery biomarkers. Estimating equations produce Corr(Q,T), Corr(M,T), Corr(P,T), conditional on assumptions about error correlations. Correlations between errors in both Q and a reference dietary measure can also be estimated if R is available. A small validation study of California Seventh-day Adventists provided food frequency, repeated 24-hour dietary recalls (R), and biological data (blood, overnight urines, and subcutaneous fat). Values of Corr(Q,T) ranged between 0.40 and 0.66. Values of Corr(R,T) were higher, between 0.48 and 0.83. Estimated correlations between errors in R and Q were all positive. When carefully chosen, M and P, rather than M and R, should better satisfy assumptions about error correlations. Food frequency data and repeated 24-hour recalls both provide estimates of T, but the latter has greater validity. Standard errors suggest that for good precision Corr(Q,T) requires large validation studies (2000-3000 subjects).

THE ASSOCIATION BETWEEN AMBIENT PARTICULATE AIR POLLUTION LEVELS AND RISK OF CARDIOPULMONARY AND ALL-CAUSE MORTALITY DURING 22 YEARS FOLLOW-UP OF A NON-SMOKING COHORT. RESULTS FROM THE AHSMOG STUDY

ISEE-81 Abstract: The relationship between ambient air pollution and cardiopulmonary mortality is currently a topic of debate. If there is a relationship, this could have great implication for policy regulations. Methods: To study the health effect of long-term ambient air pollution, a cohort of 6,338 nonsmoking, white California Seventh-day Adventists was followed with respect to mortality from 1977-1998. To be included in the study, participants must have lived within 10 miles of their 1977 address for the previous 10 years. At baseline in 1977, a comprehensive lifestyle and diet questionnaire was completed and the cohort was followed with update of residence and workplace in order to assess monthly averages of ambient air pollutants throughout the study period. Exposure to environmental tobacco smoke, dusts and fumes in the workplaces and time spent outdoors was assessed through self-administered questionnaires in 1977, 1987 and again in 1992 and 2000. The risk of cardiopulmonary mortality and all natural cause mortality was ascertained from 1977-1998 through matching with death certificates obtained from the National Death Index (NDI). Monthly indices of particulate ambient air pollutant concentrations (PM10, PM2.5, PM10-2.5) were obtained from the California Air Resource Board monitoring stations from 1973-1998 or from airport visibility measures (PM2.5), and interpolated to residence and work zip code centroids. Cox proportional hazards models with time dependent air pollution measures were used to estimate relative risks (RR) associated with an increase of 10 mg/m3 in mean concentrations of each ambient air pollutant averaged over the period 1973 to time of death. The associations were further tested in two-pollutant models with ozone added to each model. Persons with baseline stroke, CHD or diabetes were excluded from the study. The analyses were controlled for age, pack-years of past cigarette smoking, history of hypertension, BMI, years of education, diet and total exercise level. Results: Elevated risk of cardiopulmonary and all natural cause mortality was found for PM2.5 in two-pollutant models with ozone in females, but not in males.TABLE 1Conclusion: It is unclear why females show a higher sensitivity to the effects of ambient levels of PM2.5. The observed relationships could have implications for public health policy. However, further studies are needed to confirm our findings in other studies.

Regression calibration in studies with correlated variables measured with error.

Regression calibration is a technique that corrects biases in regression results in situations where exposure variables are measured with error. The existence of a calibration substudy, where accurate and crude measurement methods are related by a second regression analysis, is assumed. The cost of measurement error in multivariate analyses is loss of statistical power. In this paper, calibration data from California Seventh-day Adventists are used to simulate study populations and new calibration studies. Applying regression calibration logistic analyses, the authors estimate power for pairs of nutritional variables. The results demonstrate substantial loss of power if variables measured with error are strongly correlated. Biases in estimated effects in cases where regression calibration is not performed can be large and are corrected by regression calibration. When the true coefficient has zero value, the corresponding coefficient in a crude analysis will usually have a nonzero expected value. Then type I error probabilities are not nominal, and the erroneous appearance of statistical significance can readily occur, particularly in large studies. Major determinants of power with use of regression calibration are collinearity between the variables measured with error and the size of correlations between crude and corresponding true variables. Where there is important collinearity, useful gains in power accrue with calibration study size up to 1,000 subjects.

Ten years of life: Is it a matter of choice?

Relative risk estimates suggest that effective implementation of behaviors commonly advocated in preventive medicine should increase life expectancy, although there is little direct evidence. To test the hypothesis that choices regarding diet, exercise, and smoking influence life expectancy. A total of 34 192 California Seventh-Day Adventists (75% of those eligible) were enrolled in a cohort and followed up from 1976 to 1988. A mailed questionnaire provided dietary and other exposure information at study baseline. Mortality for all subjects was ascertained by matching to state death tapes and the National Death Index. California Adventists have higher life expectancies at the age of 30 years than other white Californians by 7.28 years (95% confidence interval, 6.59-7.97 years) in men and by 4.42 years (95% confidence interval, 3.96-4.88 years) in women, giving them perhaps the highest life expectancy of any formally described population. Commonly observed combinations of diet, exercise, body mass index, past smoking habits, and hormone replacement therapy (in women) can account for differences of up to 10 years of life expectancy among Adventists. A comparison of life expectancy when these factors take high-risk compared with low-risk values shows independent effects that vary between 1.06 and 2.74 years for different variables. The effect of each variable is assessed with all others at either medium- or high-risk levels. Choices regarding diet, exercise, cigarette smoking, body weight, and hormone replacement therapy, in combination, appear to change life expectancy by many years. The longevity experience of Adventists probably demonstrates the beneficial effects of more optimal behaviors.

Urinary 1-methylhistidine is a marker of meat consumption in Black and in White California Seventh-day Adventists.

Meat consumption predicts risk of several chronic diseases. The authors validate the accuracy of meat consumption reported by food frequency questionnaires and the mean of eight 24-hour recalls, using urinary methylhistidine excretion, in 55 Black and 71 White Adventist subjects in Los Angeles and San Diego, California, in 1994-1997. 1-Methylhistidine excretion predicts vegetarian status in Black (p = 0.02) and in White (p = 0.005) subjects. Spearman's correlation coefficients between 1-methylhistidine and estimated meat consumption were usually between 0.4 and 0.6 for both food frequency questionnaires and 24-hour recall data. This is despite the chance collection of dietary recalls and urines from omnivores on meatless days.

Relationships of mortality with the fine and coarse fractions of long-term ambient PM10 concentrations in nonsmokers.

In a cohort of 6338 California Seventh-day Adventists, we previously observed for males associations between long-term concentrations of particulate matter (PM) with an aerodynamic diameter less than 10 microm (PM10) and 15-year mortality due to all natural causes (ANC) and lung cancer (LC) listed as underlying causes of death and due to nonmalignant respiratory disease listed as either the underlying or a contributing (CRC) cause of death. The purpose of this analysis was to determine whether these outcomes were more strongly associated with the fine (PM2.5) or the coarse (PM2.5-10) fractions of PM10. For participants who lived near an airport (n=3769), daily PM2.5 concentrations were estimated from airport visibility, and on a monthly basis, PM2.5-10 concentrations were calculated as the differences between PM10 and PM2.5. Associations between ANC, CRC, and LC mortality (1977-1992) and mean PM10, PM2.5, and PM2.5-10 concentrations at study baseline (1973-1977) were assessed using Cox proportional hazards models. Magnitudes of the PM10 associations for the males of this subgroup were similar to those for the males in the entire cohort although not statistically significant due to the smaller numbers. In single-pollutant models, for an interquartile range (IQR) increase in PM10 (29.5 microg/m3), the rate ratios (RRs) and 95% confidence intervals (CI) were 1.15 (0.94, 1.41) for ANC, 1.48 (0.93, 2.34) for CRC, and 1.84 (0.59, 5.67) for LC. For an IQR increase in PM2.5 (24.3 microg/m3), corresponding RRs (95% CI) were 1.22 (0.95, 1.58), 1.64 (0.93, 2.90), and 2.23 (0.56, 8.94), and for an IQR increase in PM2.5-10 (9.7 microg/m3), corresponding RRs (95% CI) were 1.05 (0.92, 1.20), 1.19 (0.88, 1.62), and 1.25 (0.63, 2.49), respectively. When both PM25 and PM2.5-10 were entered into the same model, the PM2.5 estimates remained stable while those of PM2.5-10 decreased. We concluded that previously observed associations of long-term ambient PM10 concentration with mortality for males were best explained by a relationship of mortality with the fine fraction of PM10 rather than with the coarse fraction of PM10.

Associations between diet and cancer, ischemic heart disease, and all-cause mortality in non-Hispanic white California Seventh-day Adventists

Results associating diet with chronic disease in a cohort of 34192 California Seventh-day Adventists are summarized. Most Seventh-day Adventists do not smoke cigarettes or drink alcohol, and there is a wide range of dietary exposures within the population. About 50% of those studied ate meat products <1 time/wk or not at all, and vegetarians consumed more tomatoes, legumes, nuts, and fruit, but less coffee, doughnuts, and eggs than did nonvegetarians. Multivariate analyses showed significant associations between beef consumption and fatal ischemic heart disease (IHD) in men [relative risk (RR) = 2.31 for subjects who ate beef > or =3 times/wk compared with vegetarians], significant protective associations between nut consumption and fatal and nonfatal IHD in both sexes (RR approximately 0.5 for subjects who ate nuts > or =5 times/wk compared with those who ate nuts <1 time/wk), and reduced risk of IHD in subjects preferring whole-grain to white bread. The lifetime risk of IHD was reduced by approximately 31% in those who consumed nuts frequently and by 37% in male vegetarians compared with nonvegetarians. Cancers of the colon and prostate were significantly more likely in nonvegetarians (RR of 1.88 and 1.54, respectively), and frequent beef consumers also had higher risk of bladder cancer. Intake of legumes was negatively associated with risk of colon cancer in nonvegetarians and risk of pancreatic cancer. Higher consumption of all fruit or dried fruit was associated with lower risks of lung, prostate, and pancreatic cancers. Cross-sectional data suggest vegetarian Seventh-day Adventists have lower risks of diabetes mellitus, hypertension, and arthritis than nonvegetarians. Thus, among Seventh-day Adventists, vegetarians are healthier than nonvegetarians but this cannot be ascribed only to the absence of meat.

Age at Natural Menopause and Total Mortality and Mortality from Ischemic Heart Disease: The Adventist Health Study

We studied the relationship between age at natural menopause and total mortality as well as mortality from ischemic heart disease in a cohort of 6182 California Seventh-Day Adventist women who reported a natural menopause. During follow-up from 1976 through 1988, there were 1831 deaths. A total of 308 deaths due to ischemic heart disease occurred in women who denied ischemic heart disease at start of follow-up. An early menopause was associated with increased total mortality (P value for linear trend <0.001) and ischemic heart disease mortality (P value for linear trend = 0.03). This relationship could not be explained by possible confounding variables. Our results support the hypothesis that an early natural menopause (35–40 years old) increases the risk of ischemic heart disease. There is, however, also some evidence of increased risk of ischemic heart disease in women with a very late menopause (>55 years), particularly in women who never have used postmenopausal estrogens.

Validity of dietary recall over 20 years among California Seventh-day Adventists.

Past dietary habits are etiologically important to incident disease. Yet the validity of such measurements from the previous 10-20 years is poorly understood. In this study, the authors correlated food frequency results that were obtained in 1994-1995 but pertained to recalled diet in 1974 with the weighted mean of five random 24-hour dietary recalls obtained by telephone in 1974. The subjects studied were 72 Seventh-day Adventists who lived within 30 miles of Loma Linda, California; had participated in a 1974 validation study; were still alive; and were willing to participate again in 1994. A method was developed to allow correction for random error in the reference data when these data had differentially weighted components. The results showed partially corrected correlation coefficients of greater than 0.30 for coffee, whole milk, eggs, chips, beef, fish, chicken, fruit, and legumes. Higher correlations on average were obtained when the food frequencies were scored simply 1-9, reflecting the nine frequency categories. The 95% confidence intervals for 15 of the 28 correlations excluded zero. Incorporation of portion size information was unhelpful. The authors concluded that in this population, data recalled from 20 years ago should be treated with caution but, for a number of important foods, that the degree of validity achieved approached that obtained when assessing current dietary habits.

Development of Chronic Productive Cough as Associated with Long-Term Ambient Inhalable Particulate Pollutants (PM10) in Nonsmoking Adults: The AHSMOG Study

Abstract Standardized respiratory symptom questionnaires were completed by 3091 nonsmoking California Seventh-Day Adventists in 1977, 1987, and 1992. Ambient concentrations of air pollutants estimated included total suspended particulates (TSP), 1973–1987; particulates ⩽10 μm in diameter (PM10), indirectly estimated from TSP, 1973–1987, and directly estimated from monitored PM10, 1987–1992; suspended sulfates, 1977–1992; sulfur dioxide, 1973–1992; and 8-hour average of ozone, 1973–1992. Adjustments to ambient concentrations have been made for time spent indoors. Chronic bronchitis was defined as cough only (cough type) or with sputum production (chronic productive cough) on most days, for at least 3 months/year, for 2 years or more. Using indirect estimates of PM10 prior to 1987 and direct estimates after 1987, multiple logistic regression models adjusting for covariates have been used to study development of chronic bronchitis (235 new cases) and chronic productive cough (169 new cases) between 1977 and ...

Does high soy milk intake reduce prostate cancer incidence? The Adventist Health Study (United States)

Recent experimental studies have suggested that isoflavones (such as genistein and daidzein) found in some soy products may reduce the risk of cancer. The purpose of this study was to evaluate the relationship between soy milk, a beverage containing isoflavones, and prostate cancer incidence. A prospective study with 225 incident cases of prostate cancer in 12,395 California Seventh-Day Adventist men who in 1976 stated how often they drank soy milk. Frequent consumption (more than once a day) of soy milk was associated with 70 per cent reduction of the risk of prostate cancer (relative risk = 0.3, 95 percent confidence interval 0.1-1.0, p-value for linear trend = 0.03). The association was upheld when extensive adjustments were performed. Our study suggests that men with high consumption of soy milk are at reduced risk of prostate cancer. Possible associations between soy bean products, isoflavones and prostate cancer risk should be further investigated.

Variables associated with cognitive function in elderly California Seventh-day Adventists.

From a cohort of white, non-Hispanic California Seventh-day Adventists, 99 subjects over age 75 years in 1991 were randomly selected. Dietary habits and educational status had been measured in 1976. Subjects completed the Mini-Mental State Examination (MMSE) in 1991, and at that time, they or caregivers also gave information on current medical problems and drug therapy. Those who ate more calories in 1976 had lower MMSE scores in 1991 (p = 0.03), an association strengthened by excluding those with previous stroke or Parkinson's disease by 1991. This raises the possibility that higher consumption of calories in middle age may accelerate the decline in cognitive function seen with aging, as apparently occurs in some animals. Less-educated subjects had lower MMSE scores, especially among the very elderly. The statistical model predicts that the negative association between use of psychotropic drugs and MMSE score (p = 0.004) is particularly potent in those cognitively impaired for other reasons. If causal, this suggests that physicians should use these agents very cautiously in such subjects.

Effect of Risk Factor Values on Lifetime Risk of and Age at First Coronary Event

The effect of traditional coronary heart disease risk factors on lifetime risk, age at onset, and survival free of coronary disease has not been extensively studied. The authors have used the cohort data from 27,321 California Seventh-day Adventists who had no known heart disease in 1976 to investigate these questions. Multiple decrement life tables incorporating non-parametric estimates of conditional probabilities for both coronary disease and all other competing endpoints were used to estimate these survival outcomes. Variance estimators are provided in an appendix. Persons characterized by being either past smokers, diabetic, hypertensive, physically, non-vegetarian, or infrequent consumers of nuts often showed substantial differences in these survival outcomes. Statistically significant results include earlier age at onset of coronary disease at between 4 and 10 years, reduced life expectancy free of the disease between 5 and 9 years, and increased lifetime risk between 8% and 16%, when comparing groups with and without adverse values for different risk factors. The presence of adverse levels of two risk factors predicted even greater differences in these endpoints. These important effects are easily understood by the layman or non-epidemiologist professional, which is often not true of a relative risk. This should increase the effectiveness of such results when promoting behavioral change.

Estimated long-term ambient concentrations of PM10 and development of respiratory symptoms in a nonsmoking population.

Site- and season-specific regressions of particulates less than 10 mu in diameter (PM10) on total suspended particulates (TSPs) were formed throughout California during years when both were monitored. The regressions were then applied to monitored TSPs for the years 1973 to 1987, and indirect estimates of PM10 were formed. These estimates of PM10 were validated by interpolating them to other monitoring stations. The split-halves correlation between the estimated and monitored mean concentrations, obtained when both were first cumulated for a 2-y period, was .86. Indirect estimates of PM10 at monitoring stations were interpolated, by month, to zip code centroids of home and work location and were cumulated for a cohort of 3,914 California Seventh-day Adventist (SDA) nonsmokers. Multivariate analyses, adjusted for several covariates, showed statistically significant (p < .05), but small, positive associations between PM10 and development of (a) definite symptoms of overall airway obstructive disease, (b) chronic productive cough, and (c) increased severity of airway obstructive disease and asthma. The relative risk (RR) associated with 1,000 h/y (42 d) exposure to concentrations of PM10 that exceeded 100 micrograms/m3 for development of airway obstructive disease was 1.17 (95% confidence interval [CI]: 1.02, 1.33); for development of productive cough, the RR was 1.21 (CI 1.02, 1.44); and for development of asthma, the RR was 1.30 (CI, 0.97, 1.73). Stronger associations were observed for those who were exposed occupationally to dusts and fumes. The RR of developing airway obstructive disease as an adult for those who had airway obstructive disease as a child was 1.66 (CI 1.15, 2.33).

Long-Term Ambient Concentrations of Particulates and Oxidants and Development of Chronic Disease in a Cohort of Nonsmoking California Residents

AbstractA cohort of 6340 nonsmoking California Seventh-Day Adventists (SDAs) who had resided within 5 miles of their present residence for the past 10 yr has been followed since 1977 for incidence of cancer and myocardial infarction (MI) through 1982; development of definite symptoms of, and increasing severity of, airway obstructive disease (AOD), chronic bronchitis, and asthma through 1987; and all natural cause mortality through 1987. Cumulative ambient concentrations of specific pollutants have been estimated for study participants from 1967 to 1987 by interpolating monthly statistics from statewide air monitoring stations to ZIP codes of residence and work location. Statistics include excess concentrations and exceedance frequencies above a number of cutoffs as well as mean ambient concentration and mean ambient concentration adjusted for time spent indoors. Indoor sources or nitrogen (NO2), and of paniculate pollution such as environmental tobacco smoke, both at home and at work, as well as occupati...

Prospective studies of diet and breast cancer.

To avoid biases due to control selection and the retrospective reporting of diet that may occur in case-control studies, a series of large prospective studies have been started since about 1980 to examine the relationship between fat intake and breast cancer risk. Relative risks for the highest versus lowest categories of energy-adjusted fat intake in the six published studies have all been nonsignificant and close to 1.0: California Seventh-Day Adventists Study (215 cases), relative risk (RR) = 1.21; Nurses' Health Study (1439 cases), RR = 0.90; Canadian Breast Cancer Screening Study (592 cases), RR = 1.30; Iowa Women's Study (408 cases), RR = 1.13; New York State Cohort (359 cases), RR = 1.00; and the Dutch Cohort (471 cases), RR = 1.11. Two additional studies have been reported with fewer than 70 cases and dietary methods less appropriate for studies of this nature; an inverse association was seen in one and a positive association in the other. In studies that included both premenopausal and postmenopausal women, no evidence was seen for a stronger positive association among the older group. In addition, no indication was seen of a threshold for reduced risk below 30% of calories from fat, as has been suggested by some. Although associations with specific types of fat tended to vary somewhat among studies, in none was saturated fat significantly associated with risk of breast cancer. In summary, the evidence from prospective studies strongly suggests that a substantial association does not exist between fat intake by middle-aged women and their risk of breast cancer. A very weak association, an effect of very low fat intake, a greatly delayed effect, and an influence of fat consumption early in life are difficult to exclude. Further follow-up of these and other cohorts will provide additional resolution of these issues.

Cancer incidence among California Seventh-day Adventists, 1976–1982

Cancer incidence was monitored in a population of 34,000 Seventh-day Adventists in California. By religious belief, Adventists do not consume tobacco, alcohol, or pork and approximately one-half adhere to a lacto-ovovegetarian lifestyle. Only a small percentage are pure vegetarians. Comparisons of cancer-incidence rates in this population with an external reference population were completed by calculating standardized morbidity ratios (SMRs) for all cancer sites. Also, within the population, relative risks were calculated by using data obtained from a detailed lifestyle questionnaire that members of the study population completed. For all cancer sites combined in males, the SMR was lower in the Adventists (SMR = 0.73). The SMR was also lower in males for most individual cancer sites. However, prostate cancer risk was higher. For females, the all-cancer SMR was lower but not significantly so (SMR = 92). Most site-specific SMRs were lower, although not as much as the male SMRs. The SMR for endometrial cancer was significantly higher in female Adventists.

The Application of Results of Some Studies of California Seventh-Day Adventists to the General Population

In his editorial,¹Castelli makes the rather striking claim that Seventh-Day Adventists experience only one seventh the risk of heart attack as other Americans, thereby suggesting that the reported data²may have only limited application to the wider population. We can only assume that, in the context of the editorial, Castelli was playing on a repetition of the word<i>seven</i>, and did not intend any factual basis. Unfortunately, the misstatement was included in press releases and led to some confusion with journalists and the reading public. Contrary to the above statement by Castelli, previous comparisons of coronary heart disease (CHD) mortality suggest that California male Adventists have 50% to 70% of the CHD mortality risk, and female Adventists have 50% to 90% of the CHD mortality risk (depending on length of follow-up) of non-Adventist Californians. The non-Adventist comparison group were participants in a contemporaneous study that used similar