Biomedical subjects

D L DeMets

Publications and source records attributed to D L DeMets.

At least 55 records · Page 3Linked to original sources

PubMed1989

Changing frequency of interim analysis in sequential monitoring.

In clinical trial data monitoring, one can either introduce a discrete sequential boundary for a set of specified decision times or adopt a use function and then derive the boundary when data are monitored. If the use function approach is employed, one can adjust the frequency of data monitoring as long as the decision is not data-dependent. However, if the frequency of future data monitoring is affected by the observed data, then the probability of Type I error will no longer be preserved exactly. But the effect on the significance level and power is very small, perhaps negligible, as indicated by simulation results.

Biometry↗

PubMed1989

Factors associated with visual outcome after photocoagulation for diabetic retinopathy. Diabetic Retinopathy Study Report #13.

Six risk factors for severe visual loss despite panretinal (scatter) photocoagulation were identified by analyzing data collected during the first 5 years after randomization in the Diabetic Retinopathy Study. Proportional hazards regression revealed NVD (neovascularization on/around the optic disc) to be the most important risk factor. The risk of severe visual loss rose with increasing NVD, hemorrhages/microaneurysms, retinal elevation, proteinuria, and hyperglycemia and fell with increasing "treatment density." These results are similar to previous DRS findings on untreated eyes. The importance of "treatment density" as an independent predictor of visual outcome is a new finding and lends support to the common clinical practice of repeating photocoagulation if initial treatment does not reduce or stabilize retinal neovascularization.

Aged↗

PubMed1989

Relation of ocular and systemic factors to survival in diabetes.

The relationship of survival to systemic and ocular factors in diabetic persons was studied using data collected as part of the Wisconsin Epidemiologic Study of Diabetic Retinopathy. Six years after the baseline examination, 9.5% of 996 insulin-taking people who were younger than age 30 years when their diabetes was diagnosed (younger onset) had died. Of 1370 people whose diabetes was diagnosed after age 30 years (older onset), 35.3% had died. After adjusting for age and sex, longer duration of diabetes, presence of proteinuria, a history of cardiovascular disease, higher blood pressure, diuretic use, a history of smoking, poorer visual acuity, and more severe retinopathy were significantly associated with decreased survival in both groups. Glaucoma was associated with decreased survival in the younger onset group and cataract in the older onset group. These findings suggest that some ocular complications are important risk indicators for death. Their presence in diabetic patients suggests the need for frequent examinations to detect systemic complications and to intervene to minimize their effect.

Adult↗

PubMed1988

Glycosylated hemoglobin predicts the incidence and progression of diabetic retinopathy.

The relationship between hyperglycemia, measured by glycosylated hemoglobin at the initial examination, and the four-year incidence and progression of diabetic retinopathy was examined in a population-based study in Wisconsin. Younger- (n = 891) and older-onset (n = 987) persons participating in baseline and follow-up examinations were included. Glycosylated hemoglobin was measured by microcolumn. Retinopathy was determined from stereoscopic fundus photographs. In the younger-onset group, comparing the highest with the lowest quartile of glycosylated hemoglobin, the relative risk for developing any diabetic retinopathy was 1.9; for proliferative retinopathy, 21.8; and for progression, 4.0. Among older-onset persons taking insulin, the corresponding relative risks were 1.9, 4.0, and 2.1. Among older-onset persons not taking insulin, relative risks were 4.0 for any retinopathy and 6.2 for progression. A positive relationship between incidence and progression of retinopathy and glycosylated hemoglobin remained after controlling for duration of diabetes, age, sex, and baseline retinopathy. These data suggest a strong and consistent relationship between hyperglycemia and incidence and progression of retinopathy.

Adult↗

PubMed1988

Proteinuria in diabetes.

In a population-based study in southern Wisconsin, 1370 diabetic persons diagnosed after 29 years of age were examined using standard protocols to determine the prevalence of proteinuria and associated risk variables. Proteinuria (greater than or equal to 0.30 g/L) was present in 18.0% of persons taking insulin and 12.2% of the persons not taking insulin. Proliferative retinopathy and proteinuria were associated with each other. Proteinuria was also associated with increasing duration of diabetes, high systolic blood pressure, use of digoxin, and being male, but not with a history of cigarette smoking or metabolic control as measured by glycosylated hemoglobin.

Adult↗

PubMed1987

Recruitment experience in the Nocturnal Oxygen Therapy Trial.

The Nocturnal Oxygen Therapy Trial was a randomized controlled clinical trial sponsored by the National Heart, Lung, and Blood Institute and carried out by six clinics. The primary objective was to compare, in patients with advanced chronic obstructive pulmonary disease, the effectiveness of 24 hours of oxygen administration to that of 12 hours of oxygen administration including the patient's usual period of sleep. Some patients entering the period of baseline observation were not eligible for randomization at the end of the baseline period. Such attrition is discussed relative to setting goals for the number of patients to enter such an observation period. The impact of an enrollment rate less than what was originally projected is discussed relative to changes in the eligibility criteria and relative to the decision as to whether to extend the recruitment period.

Clinical Trials as Topic↗

PubMed1987

The Wisconsin Epidemiologic Study of Diabetic Retinopathy. VII. Diabetic nonproliferative retinal lesions.

The prevalences of hard exudates, soft exudates, intraretinal microvascular abnormalities (IRMAs), and venous beading and their relationships to demographic and other characteristics were examined in a population-based study in southern Wisconsin. For participants whose age at diagnosis was less than 30 years and who were taking insulin (N = 996), hard exudates were found in 24.2%, soft exudates in 15.3%, IRMAs in 16.5%, and venous beading in 7.0% of the population. For participants whose age at diagnosis was 30 years or older and who were taking insulin (N = 674), hard exudates were found in 28.3%, soft exudates in 15.5%, IRMAs in 8.8%, and venous beading in 3.2%. For older-onset persons not taking insulin (N = 696), hard exudates were found in 9.4%, soft exudates in 5.4%, IRMAs in 2.6%, and venous beading in 0.9% of the population. The severities of the lesions were found to be consistently associated with longer duration of diabetes in younger-onset persons and the presence of proteinuria in older-onset persons.

Cross-Sectional Studies↗

PubMed1987

The Wisconsin Epidemiologic Study of Diabetic Retinopathy. VI. Retinal photocoagulation.

The prevalence of focal and panretinal photocoagulation and its relationship to demographic and other characteristics were examined in a population-based study in southern Wisconsin. For participants whose age at diagnosis was less than 30 years and who were taking insulin (996 persons) the prevalence rate of panretinal photocoagulation (13.9%) was higher than that of focal photocoagulation (3.6%). For those whose age at diagnosis was 30 years or older (1370 persons), the prevalence rate for panretinal photocoagulation (3.6%) was slightly higher than that of focal photocoagulation (3.0%). Seventy-two percent of eyes of younger onset and 45% of eyes of older onset persons that had received panretinal photocoagulation treatment were found to have incomplete regression of retinal new vessels, and in approximately half of these eyes severe proliferative retinopathy (Diabetic Retinopathy Study High Risk Characteristics [DRS-HRC]) was present. Among eyes with DRS-HRC, 55% were found to be untreated.

Adult↗

PubMed1987

Confidence intervals following group sequential tests in clinical trials.

Tsiatis, Rosner, and Mehta (1984, Biometrics 40, 797-803) proposed a procedure for constructing confidence intervals following group sequential tests of a normal mean. This method is first extended for group sequential tests for which the sample sizes between interim analyses are not identical or the times are not equally spaced. Then properties of this confidence interval estimation procedure are studied by simulation. The extension accommodates the flexible procedure by Lan and DeMets (1983, Biometrika 70, 659-663) for constructing discrete group sequential boundaries to form a structure for monitoring and estimation following a class of group sequential tests. Finally, it is demonstrated how to combine the procedures by Lan and DeMets and by Tsiatis, Rosner, and Mehta using a FORTRAN program.

Biometry↗

PubMed1986

The validity of a survey question to study diabetic retinopathy.

This report presents the results of a comparison between information obtained from response to the question "Have you been told that the diabetes has affected the back of your eyes, that is, the retina?" and the determination of the severity of retinopathy by grading of stereoscopic fundus photographs. Both "younger onset" (n = 996) and "older onset" (n = 1,370) persons who participated in a large population-based study of diabetic persons in southern Wisconsin from 1980-1982 were included. For the younger onset persons, 31.1% responded positively, while 70.7% were found to have retinopathy. The sensitivity of the questionnaire response varied from 17.8% for persons with mild nonproliferative retinopathy to 81.9% for persons with proliferative retinopathy. The specificity was 97.3%. For the older onset persons, 14.9% responded positively, while 54.2% were found to have retinopathy. The sensitivity of the question varied from 9.9% for persons with mild nonproliferative retinopathy to 68.7% for persons with proliferative retinopathy. The specificity was 93.3%. The question used in this survey provides a highly specific measure of prevalence; it is most sensitive for proliferative retinopathy.

Adult↗

PubMed1985

The Wisconsin Epidemiologic Study of Diabetic Retinopathy. A comparison of retinopathy in younger and older onset diabetic persons.

In a population-based survey of diabetic persons, retinopathy was detected by stereoscopic color fundus photography in 70% of persons under 30 years of age at diagnosis and taking insulin (Group YO), in 62% of persons 30 years of age or older at diagnosis and taking insulin (Group OO-I) and in 36% of persons 30 years of age or older at diagnosis not taking insulin (Group OO-N). The mean duration of known diabetes was 14.6 years in Group YO, 11.0 years in Group OO-I and 6.9 years in Group OO-N. After 20 years of diabetes, proliferative retinopathy was present in about 50% of Group YO, about 25% of Group OO-I and about 5% of Group OO-N. After 15 years of diabetes, macular edema was present in about 18% of Group YO, about 20% of Group OO-I and about 12% of Group OO-N. When present, macular edema tended to be associated with more hard exudate in Group OO-N.

Adult↗

PubMed1985

Blood pressure and hypertension in diabetes.

Blood pressure was measured in a population-based study of diabetic retinopathy in southern Wisconsin. Persons diagnosed prior to 30 years of age and taking insulin (younger onset, n = 996) and those diagnosed at 30 years of age or older (older onset, n = 1,370) were examined. Blood pressures were measured by a standard protocol using a random-zero sphygmomanometer. In both groups of patients, systolic blood pressure increased with increasing age and tended to be higher in older onset than younger onset persons. Hypertension was present in 21.9% of the younger and 58.1% of the older onset group. Older age at examination, presence of proteinuria, larger body mass, gender, and longer duration of diabetes were significantly associated with higher systolic blood pressure.

Adolescent↗

PubMed1985

Use of logrank tests and group sequential methods at fixed calendar times.

This paper presents simulations to determine the operating characteristics of several group sequential boundaries when applied to the repeated analysis of survival data at equal intervals of calendar time. Because the group sequential boundaries of Pocock (1977, Biometrika 64, 191-199) and O'Brien and Fleming (1979, Biometrics 35, 549-556) were constructed on the assumption that each interim analysis provides an equal increment of statistical information, these boundaries are not theoretically appropriate for interim analysis at prescheduled calendar times. Nonetheless, our simulations show that these boundaries yield size and power near nominal levels for repeated logrank analyses at equal intervals of calendar time.

Biometry↗

PubMed1984

The Wisconsin epidemiologic study of diabetic retinopathy. II. Prevalence and risk of diabetic retinopathy when age at diagnosis is less than 30 years.

In a population-based study in southern Wisconsin, 996 insulin-taking, younger-onset diabetic persons were examined using standard protocols to determine the prevalence and severity of diabetic retinopathy and associated risk variables. The prevalence of diabetic retinopathy varied from 17% to 97.5% in persons with diabetes for less than five years and 15 or more years, respectively. Proliferative retinopathy varied from 1.2% to 67% in persons with diabetes for less than ten years and 35 or more years, respectively. For persons with diabetes of 10 years' duration or less, the Cox regression model relates the severity or retinopathy to longer duration, older age at examination, and higher levels of glycosylated hemoglobin. After ten years of diabetes, severity of retinopathy was related to longer duration, high levels of glycosylated hemoglobin, presence of proteinuria, higher diastolic BP, and male sex.

Adolescent↗

PubMed1984

The Wisconsin epidemiologic study of diabetic retinopathy. III. Prevalence and risk of diabetic retinopathy when age at diagnosis is 30 or more years.

In a population-based study in southern Wisconsin, 1,370 patients given diagnoses of diabetes at age 30 years or older were examined using standard protocols to determine the prevalence and severity of diabetic retinopathy and associated risk variables. The prevalence of diabetic retinopathy varied from 28.8% in persons who had diabetes for less than five years to 77.8% in persons who had diabetes for 15 or more years. The rate of proliferative diabetic retinopathy varied from 2.0% in persons who had diabetes for less than five years to 15.5% in persons who had diabetes for 15 or more years. By using the Cox regression model, the severity of retinopathy was found to be related to longer duration of diabetes, younger age at diagnosis, higher glycosylated hemoglobin levels, higher systolic BP, use of insulin, presence of proteinuria, and small body mass.

Aged↗

PubMed1984

The Wisconsin epidemiologic study of diabetic retinopathy. IV. Diabetic macular edema.

The prevalence of macular edema and its relationship to a number of risk factors were examined in a population-based study in southern Wisconsin. Macular edema was determined from its presence on stereoscopic fundus photographs or from past history as recorded and documented in clinic records and photographs. For participants whose age at diagnosis of diabetes was less than 30 years and who were taking insulin (n = 919), prevalence rates of macular edema varied from 0% in those who had diabetes less than 5 years to 29% in those whose duration of diabetes was 20 or more years. In these persons, macular edema was associated with longer duration of diabetes, presence of proteinuria, diuretic use, male gender and higher glycosylated hemoglobin. For those whose age at diagnosis was 30 years or older (n = 1121), prevalence rates of macular edema varied from 3% in those who had diabetes less than 5 years to 28% in those whose duration of diabetes was 20 or more years. In these persons, presence of macular edema was associated with longer duration of diabetes, higher systolic blood pressure, insulin use, higher glycosylated hemoglobin, and presence of proteinuria.

Adolescent↗

PubMed1984

Statistical aspects of early termination in the beta-blocker heart attack trial.

The Beta-Blocker Heart Attack Trial was a randomized double blind controlled trial comparing propranolol with placebo in 3837 patients with a recent myocardial infarction. The trial was terminated on recommendation of the Policy and Data Monitoring Board 9 months before the scheduled closing date. The propranolol group, at the time of the decision, had a 26% lower mortality (z = 2.82). Many issues were considered in this decision. These included the magnitude of the overall results; consistency of results across subgroups, clinical centers, and cause of death; and completeness of follow-up. Two basic statistical methods were used in declaring the overall mortality results significant. The first method evaluated the current survival data taking into account the issue of repeated significance testing. The second method evaluated whether the observed trend was so impressive that the conclusion was unlikely to change even if the trial should continue to the scheduled end. These two methods, as well as other considerations led to the recommendation to discontinue the trial.

Adrenergic beta-Antagonists↗

PubMed1984

Prevalence of diabetes mellitus in southern Wisconsin.

The prevalence of known cases of diabetes was ascertained from patient records in an 11-county area in Wisconsin in July 1979 to June 1980. The prevalence in the noninstitutionalized population was found to be 1%. Prevalence rates rose from 0.5 cases per 1000 population in the first decade of life to 44.7 cases per 1000 population in the eighth decade. The highest rates were found in the nursing home population. Males had higher age-adjusted rates than females. No difference in prevalence was found between persons living in metropolitan or nonmetropolitan counties. Determination of prevalence by these methods is a rapid and inexpensive means of ascertainment of known cases of diabetes.

Adolescent↗