Biomedical subjects

Mari Palta

Publications and source records attributed to Mari Palta.

At least 19 recordsLinked to original sources

PubMed2006

Lower-than-expected prevalence and severity of retinopathy in an incident cohort followed during the first 4-14 years of type 1 diabetes: the Wisconsin Diabetes Registry Study.

The authors examined the development of diabetic retinopathy in a population-based cohort of persons with incident type 1 diabetes to investigate the possibility of lowered retinopathy prevalence and severity compared with previous US studies. A total of 474 diabetic persons from Wisconsin were followed from diagnosis through 4-14 years' duration during 1990-2002. Retinopathy was determined by fundus photography at 4, 7, 9, and 14 years' duration. Risk of developing retinopathy was modeled on demographic and diabetes-care characteristics by means of a generalized linear model using the complementary log-log link for interval-censored data. Prevalence of retinopathy increased with duration of diabetes, from 6% at 4 years to 73% at 14 years, and was highest among adults (> or =20 years of age). Risk of developing retinopathy increased with increasing duration, worse glycemic control, and age up to 20 years. Indicators of diabetes care were related to retinopathy through their effect on glycemic control. Improvements in diabetes care leading to better glycemic control may have contributed to the much lower prevalence and less severe retinopathy observed than expected on the basis of a previous report from the same region of Wisconsin. The observed decreased prevalence has important implications for persons with type 1 diabetes, since retinopathy is a serious microvascular complication.

Adolescent↗

PubMed2006

Properties of R(2) statistics for logistic regression.

Various R(2) statistics have been proposed for logistic regression to quantify the extent to which the binary response can be predicted by a given logistic regression model and covariates. We study the asymptotic properties of three popular variance-based R(2) statistics. We find that two variance-based R(2) statistics, the sum of squares and the squared Pearson correlation, have identical asymptotic distribution whereas the third one, Gini's concentration measure, has a different asymptotic behaviour and may overstate the predictivity of the model and covariates when the model is mis-specified. Our result not only provides a theoretical basis for the findings in previous empirical and numerical work, but also leads to asymptotic confidence intervals. Statistical variability can then be taken into account when assessing the predictive value of a logistic regression model.

Biometry↗

PubMed2006

Validation of a carotid intima-media thickness border detection program for use in an office setting.

BACKGROUND: A unique semiautomated border detection program (BDP) designed for use on a personal computer was evaluated to determine whether: (1) carotid intima-media thickness (CIMT) measurements were bioequivalent to a reference laboratory; and (2) it would allow a novice (NOV) reader with no medical training to accurately and reproducibly measure CIMT. METHODS: Far-wall CIMT was measured blindly and in duplicate by an experienced and NOV reader using BDP and by a reference laboratory. RESULTS: Mean CIMT using BDP was bioequivalent to the reference laboratory (two 1-sided T-test, P < .05) with small absolute differences (experienced 0.011 +/- 0.004 mm, NOV 0.022 +/- 0.004 mm). Reproducibility was high, with small coefficients of variation when used by either the experienced (3.1%) or NOV (7.8%) reader. CONCLUSION: CIMT measurements using BDP were accurate and reproducible. It was mastered easily by a NOV reader and appeared suitable for use in an office setting.

Adult↗

PubMed2006

School achievement in a regional cohort of children born very low birthweight.

Children born very low birthweight (VLBW, <=1500 g) have historically had lower average school achievement than their normal birthweight peers. However, perinatal care and survival have changed dramatically since prior cohorts accrued, prompting reassessment. Surfactant therapy became generally available 8/1/1990, and the use of ante- and postnatal steroids increased substantially around this time. Standardized test scores and teacher ratings in math, reading, science, and social studies were obtained at age 10 for a cohort of children admitted to six regional NICUs in Wisconsin and Iowa, 8/1/1988 - 6/30/1991. We compared achievement between the VLBW cohort and controls from the same school districts. Among VLBW children, we determined neonatal and early childhood factors associated with achievement on standardized tests (ordinal logistic regression) and teacher ratings (linear regression) and evaluated whether achievement differed by birth year. Compared to population controls, VLBW children's greatest deficits occurred in mathematics. Scores on the standardized math exam and teacher ratings of overall achievement were positively associated with birthweight, social function measured at age five, and socioeconomic status. VLBW children born in the post-surfactant era (after 8/1/1990) had lower achievement on the standardized math exam than children born during the pre-surfactant era of the prior two years. Lower achievement in the post-surfactant era may be due to greater survival among less healthy neonates or increased exposure to postnatal steroids. VLBW children more likely to struggle academically could be identified by early childhood measures, allowing for targeted interventions to mitigate their difficulties.

Achievement↗

PubMed2005

The association of increased total glycosylated hemoglobin levels with delayed age at menarche in young women with type 1 diabetes.

CONTEXT: Delayed menarche is associated with subsequent reproductive and skeletal complications. Previous research has found delayed growth and pubertal maturation with type 1 diabetes and poor glycemic control. The effect of diabetes management on menarche is important to clarify, because tighter control might prevent these complications. OBJECTIVE: The objective of this study was to investigate age at menarche in young women with type 1 diabetes and examine the effect of diabetes management [e.g. total glycosylated hemoglobin (GHb) level, number of blood glucose checks, insulin therapy intensity, and insulin dose] on age at menarche in those diagnosed before menarche. DESIGN: The Wisconsin Diabetes Registry Project is a follow-up study of a type 1 diabetes population-based incident cohort initially enrolled between 1987 and 1992. SETTING: This study was performed in 28 counties in south-central Wisconsin. PATIENTS OR OTHER PARTICIPANTS: The study participants were recruited through referrals, self-report, and hospital/clinic ascertainment. Individuals with newly diagnosed type 1 diabetes, less than 30 yr old, were invited to participate. Of 288 young women enrolled, 188 reported menarche by 2002; 105 were diagnosed before menarche. INTERVENTIONS: There were no interventions. MAIN OUTCOME MEASURE: The main outcome measure was age at menarche. RESULTS: Mean age at menarche was 12.78 yr, compared with 12.54 yr in the United States (P = 0.01). Ages at menarche and diagnosis were not associated. For those diagnosed before menarche, age at menarche was delayed 1.3 months with each 1% increase in mean total GHb level in the 3 yr before menarche. CONCLUSIONS: Age at menarche was moderately delayed in young women with type 1 diabetes. Delayed menarche could potentially be minimized with improved GHb levels.

Adolescent↗

PubMed2005

A semiautomated ultrasound border detection program that facilitates clinical measurement of ultrasound carotid intima-media thickness.

We have developed a novel, semiautomated carotid intima-media thickness (CIMT) border detection program (AUTO) and evaluated its measurement reproducibility and accuracy. Images from 6 carotid segments were acquired in 50 subjects, for a total of 300 segments. Mean and maximum CIMT values were measured blindly at a reference (REF) lab and in duplicate by experienced (EXP) and novice (NOV) readers using manual (MAN) and AUTO methods. Coefficients of variation for AUTO measurements of mean (3.2%) and maximum (4.1%) CIMT were low, and the AUTO method improved the NOV reader's reproducibility. Compared with the REF lab, mean (0.012 +/- 0.006 mm) and maximum (0.144 +/- 0.006 mm) CIMT biases were small and equivalent to those of the REF lab ( P < .001). The AUTO method shortened reading times by 35% to 46% ( P < .001). We conclude that our novel AUTO CIMT measurement program improved reproducibility and was accurate. Compared with MAN tracing, the AUTO method agreed better with the REF lab and decreased reading time.

Adult↗

PubMed2005

A longitudinal measurement error model with a semicontinuous covariate.

Covariate measurement error in regression is typically assumed to act in an additive or multiplicative manner on the true covariate value. However, such an assumption does not hold for the measurement error of sleep-disordered breathing (SDB) in the Wisconsin Sleep Cohort Study (WSCS). The true covariate is the severity of SDB, and the observed surrogate is the number of breathing pauses per unit time of sleep, which has a nonnegative semicontinuous distribution with a point mass at zero. We propose a latent variable measurement error model for the error structure in this situation and implement it in a linear mixed model. The estimation procedure is similar to regression calibration but involves a distributional assumption for the latent variable. Modeling and model-fitting strategies are explored and illustrated through an example from the WSCS.

Blood Pressure↗

PubMed2004

Cardiovascular disease, mortality, and retinal microvascular characteristics in type 1 diabetes: Wisconsin epidemiologic study of diabetic retinopathy.

BACKGROUND: Diabetic retinopathy and proteinuria, manifestations of microvascular abnormalities, occur early in the course of diabetes mellitus; in contrast, macrovascular cardiovascular complications usually occur later. Retinal vessel characteristics may be informative about risk of cardiovascular disease in persons with diabetes. We evaluated this in a longitudinal cohort study of persons with type 1 diabetes. METHODS: The population consisted of persons with type 1 diabetes who were receiving care in 11 counties in Wisconsin. Subjects (n = 996) were examined at baseline (1980-1982), and 4, 10, 14, and 20 years later. Evaluations included medical history and measurements of height, weight, blood pressure, and glycosylated hemoglobin. Fundus photographs were graded for diabetic retinopathy at baseline, and the same photographs were graded later for the diameters of retinal blood vessels. At each examination, a history of cardiovascular disease events since the last examination (and prior to baseline) was obtained. Mortality was monitored yearly. RESULTS: The 20-year age-adjusted cumulative incidences were 18.1% for angina, 14.8% for myocardial infarction, and 5.9% for stroke. Severity of diabetic retinopathy was associated with angina and stroke. Arteriovenous ratio was associated with myocardial infarction. Of 273 deaths, 176 involved heart disease. The severity of retinopathy and arteriovenous ratio was associated with heart disease mortality. Nephropathy was more informative about the cardiovascular end points than were the blood vessel characteristics. CONCLUSIONS: Incidences of cardiovascular disease, including mortality, were common in people with type 1 diabetes during a 20-year interval. Retinal vascular characteristics were associated with these end points, but this association was confounded by nephropathy.

Adolescent↗

PubMed2004

A measurement error model with a Poisson distributed surrogate.

We study a linear model in which one of the covariates is measured with error. The surrogate for this covariate is the event count in unit time. We model the event count by a Poisson distribution, the rate of which is the unobserved true covariate. We show that ignoring the measurement error leads to inconsistent estimators of the regression coefficients and propose a set of unbiased estimating equations to correct the bias. The method is computationally simple and does not require using supplemental data as is often the case in other measurement error analyses. No distributional assumption is made for the unobserved covariate. The proposed method is illustrated with an example from the Wisconsin Sleep Cohort Study.

Bias↗

PubMed2004

Self-rated health among young people with type 1 diabetes in relation to risk factors in a longitudinal study.

Care for type 1 diabetes mellitus should both alleviate the physical complications of the disease and improve overall quality of life. The Wisconsin Diabetes Registry, comprising a population-based cohort that is followed longitudinally from diagnosis of type 1 diabetes, provided the authors with a unique opportunity to examine quality of life in children, adolescents, and young adults with type 1 diabetes and its relation to both sociodemographic and clinical risk factors. The authors analyzed data from 1987-2002 with a mean of 10.2 years' duration of diabetes (n = 569). They used ordinal-scaled self-rated global health as a measure of quality of life. In this paper, they propose a random-effects model for drawing inferences on individuals regarding the relation of longitudinally measured quality of life to multiple risk factors. Results showed that male gender, higher parental socioeconomic level, younger age at diabetes diagnosis, shorter diabetes duration, no hospitalization in the preceding 6 months, lower glycosylated hemoglobin level, and questionnaire responses by a person other than the subject were independently associated with better reported health. The authors found that individuals varied in their reported health even after adjustment for all identified risk factors. This could imply either that there is variability in perception even with the same health status or that there are independent unmeasured risk factors for poor health in persons with type 1 diabetes.

Adolescent↗

PubMed2004

The relation of retinal vessel caliber to the incidence and progression of diabetic retinopathy: XIX: the Wisconsin Epidemiologic Study of Diabetic Retinopathy.

OBJECTIVE: To describe the relation of retinal arteriolar and venular caliber to the incidence and progression of diabetic retinopathy in people with type 1 diabetes mellitus. DESIGN: Incidence findings in a population-based study of diabetic retinopathy in Wisconsin. Participants included 996 persons diagnosed as having diabetes mellitus before 30 years of age who took insulin and underwent the baseline examination, 891 in the 4-year follow-up, 765 in the 10-year follow-up, and 634 in the 14-year follow-up. Retinal photographs of 7 standard fields were taken at all examinations. Computer-assisted grading was performed from a digitized image of field 1 to determine the average diameter of retinal arterioles and venules and their ratio. Main outcome measures included incidence and progression of retinopathy, incidence of proliferative retinopathy, and macular edema. RESULTS: While adjusting for other factors, larger arteriolar (relative risk [RR] for the fourth vs first quartile range, 2.04; 95% confidence interval [CI], 1.20-3.47; test of trend, P =.008) and venular diameters (RR, 2.33; 95% CI, 1.37-3.95; test of trend, P =.005) were associated with greater 4-year progression of retinopathy. Larger venular diameters (RR, 4.28; 95% CI, 1.50-12.19; test of trend, P =.006) but not arteriolar diameters were associated with greater 4-year incidence of proliferative retinopathy. In multivariable analyses, arteriolar and venular calibers were not associated with the 4-year incidence of retinopathy. While adjusting for other factors, arteriolar and venular calibers were not associated with incidence of macular edema at 4 years. There were few associations of arteriolar or venular caliber with the 10- or 14-year incidence or the progression of retinopathy. CONCLUSIONS: Larger arteriolar and venular caliber, independent of retinopathy severity level, is related to the progression of retinopathy, and larger venular caliber is associated with the 4-year incidence of proliferative retinopathy. Caliber of retinal vessels is not associated with incident retinopathy. These data suggest a quantitative measure of retinal vascular caliber provides additional information regarding risk for progression of retinopathy.

Adult↗

PubMed2004

Outcomes monitoring of health, behavior, and quality of life after nutrition intervention in adults with type 2 diabetes.

OBJECTIVES: To examine changes in health and lifestyle indicators over 6 months in persons with type 2 diabetes mellitus receiving nutrition counseling from a registered dietitian, and to promote dietetics professionals' participation in outcomes monitoring and research. DESIGN: Prospective, noncontrolled descriptive study. SUBJECTS: Two hundred forty-four physician-referred adults with type 2 diabetes mellitus from 31 sites who received usual and customary nutrition counseling, and 83 registered dietitians. MAIN OUTCOME MEASURES: Glycemic control, coronary heart disease risk, self-management behaviors, and quality of life were measured at baseline, 3 months, and 6 months. Dietitians' perceptions of the study were also measured. STATISTICAL ANALYSIS: Repeated-measures analysis of variance, paired t test, Wilcoxon signed rank test, sign test, Spearman correlation, and chi 2 analysis were conducted. RESULTS: Weight and glycemic control, coronary heart disease risk, and self-management behaviors improved significantly between baseline and 3 months and baseline and 6 months. Weight, body mass index, and glycosylated hemoglobin value also improved significantly between 3 months and 6 months. Increased time and/or number of sessions with the registered dietitian were associated with weight loss and reduced glycosylated hemoglobin, fasting plasma glucose, total cholesterol, and triglyceride levels. Self-perceived health status and missed workdays were significantly improved at 6 months. Difficulty obtaining current laboratory values, lack of time, and inability to reach subjects for follow-up presented the greatest obstacles for the dietitians. CONCLUSIONS: Positive outcomes were observed in adults receiving nutrition intervention for type 2 diabetes. Clinical improvements were greatest between baseline and 3 months, with stabilization between 3 months and 6 months, suggesting ongoing intervention is needed to support continued clinical progress. Dietitians found participation in this state affiliate-coordinated research project rewarding.

Adult↗

PubMed2004

Relation between intake of vitamins C and E and risk of diabetic retinopathy in the Atherosclerosis Risk in Communities Study.

BACKGROUND: The potential protective effect of vitamins C and E against the development of diabetic retinopathy has not been thoroughly evaluated in epidemiologic studies. OBJECTIVE: The objective was to study the association between prevalent diabetic retinopathy and intake of vitamins C and E in participants of the Atherosclerosis Risk in Communities Study. DESIGN: A total of 1353 subjects with type 2 diabetes diagnosed between 1993 and 1995 or before were included. Nutrient intake was assessed with a food-frequency and supplement questionnaire administered between 1987-1989 and 1993-1995. Prevalent retinopathy (n = 224) was determined in 1993-1995 from graded fundus photographs. RESULTS: No association of retinopathy with intake of vitamin C or E from food alone or from food and supplements combined was observed. The odds ratios and 95% CIs for retinopathy for quartile 4 compared with quartile 1 of vitamins C and E intakes from food and supplements combined were 1.1 (0.7, 1.9) and 1.3 (0.8, 2.2), respectively, after adjustment for diabetes treatment and serum glucose. There was a significant interaction of the observed relations with serum glucose concentration (P < 0.05). Additionally, a decreased odds of retinopathy was found among users (reported use > or =3 y before 1993-1995) of vitamin C or E supplements or multisupplements compared with reported use of no supplements: 0.5 (0.3, 0.8), 0.5 (0.2, 0.8), and 0.4 (0.2, 0.9), respectively. CONCLUSION: No significant overall associations were observed between risk of retinopathy and intake of major dietary antioxidants. The observed association between risk of retinopathy and supplement use may reflect nondietary factors or a possible benefit of supplementation.

Antioxidants↗

PubMed2003

Postmenopausal hormone therapy and its association with cognitive impairment.

BACKGROUND: Cognitive impairment is a common and potentially debilitating medical problem in older women. Postmenopausal hormone therapy (HT) has been associated with better cognitive function, but the literature is conflicting. Results of recent trials suggest that HT is inappropriate for prevention of heart disease, and we sought to determine the role of HT in the risk of cognitive impairment. METHODS: We measured HT use and cognitive function in a population-based cohort of 1462 postmenopausal women participating in the 5-year follow-up examination for the Epidemiology of Hearing Loss Study in 1998-2000. The cohort was defined in 1987-1988 by residency in Beaver Dam, Wis, and an age of 43 to 84 years. Women had also participated in the Beaver Dam Eye Study baseline examination in 1988-1990. Use of HT was assessed at the Beaver Dam Eye Study baseline (1988-1990), 5-year follow-up (1993-1995), and 10-year follow-up (1998-2000) visits. Cognitive impairment was defined as a low Mini-Mental State Examination score or a reported diagnosis of Alzheimer disease. RESULTS: Six percent of participants (n = 94) were impaired; these women were significantly older and less educated than those who were unimpaired. In age- and education-adjusted analysis, current HT use was not significantly associated with cognitive impairment (odds ratio, 0.6; 95% confidence interval, 0.2-1.3). Similarly, cognitive impairment was not associated with past HT use or duration of HT use. CONCLUSION: In this large population-based study, postmenopausal hormone therapy was not significantly associated with better cognitive function.

Adult↗

PubMed2003

Relations of serum ascorbic acid and alpha-tocopherol to diabetic retinopathy in the Third National Health and Nutrition Examination Survey.

The protective relation of ascorbic acid and alpha-tocopherol to the development of diabetic retinopathy has not been thoroughly evaluated in epidemiologic studies. The association of prevalent diabetic retinopathy with serum ascorbic acid and alpha-tocopherol was studied among participants with type 2 diabetes (>or=40 years) (n = 998) in the Third National Health and Nutrition Examination Survey (1988-1994); 20% of the sample (n = 199) had prevalent retinopathy. The overall odds ratio for retinopathy among participants in quartile 4 compared with quartile 1 for serum ascorbic acid was 1.3 (95% confidence interval: 0.8, 2.3), with a p for trend = 0.60 after adjustment for the confounders of smoking, race, waist/hip ratio, hypertension, and duration of diabetes. The overall odds ratio for retinopathy among participants in quartile 4 compared with quartile 1 for serum alpha-tocopherol was 2.7 (95% confidence interval: 1.6, 4.6), with a p for trend = 0.14 after adjustment for confounders. After removal of supplement users of vitamin C (n = 307) or vitamin E (n = 298), the odds ratio changed direction or was attenuated: adjusted odds ratios for retinopathy among participants in quartile 4 compared with quartile 1 for serum ascorbic acid and alpha-tocopherol = 0.7 (95% confidence interval: 0.3, 1.4) and 1.6 (95% confidence interval: 0.9, 2.9), respectively. In summary, no significant associations were observed between serum levels of major dietary antioxidants and retinopathy. Recent use of supplements for treatment of complications of diabetes may explain the direct associations.

Adult↗

PubMed2003

Retinal vascular abnormalities in persons with type 1 diabetes: the Wisconsin Epidemiologic Study of Diabetic Retinopathy: XVIII.

PURPOSE: To describe the distribution of retinal vascular characteristics and their correlates in people with type 1 diabetes. DESIGN: Population-based study with baseline cross-sectional findings. PARTICIPANTS: Nine hundred ninety-six persons who were diagnosed with diabetes before 30 years of age and who were taking insulin in an 11-county area in south-central Wisconsin participated in the baseline examination from 1980 to 1982. In addition, 225 persons without diabetes participated. METHODS: Retinal photographs of 7 standard fields were taken; lightbox grading was performed to determine arteriovenous (A/V) nicking and focal retinal arteriolar narrowing. Computer-assisted grading was performed from a digitized image of field 1 to determine central retinal arteriolar equivalent (CRAE), central retinal venular equivalent (CRVE), and the arteriole-to-venule ratio (AVR). MAIN OUTCOME MEASURES: Frequency and distribution of A/V nicking, CRAE, CRVE, AVR, and focal retinal arteriolar narrowing. RESULTS: In multivariate analyses, retinopathy severity, mean arterial blood pressure, presence of gross proteinuria, glycosylated hemoglobin, and history of cardiovascular disease were associated with CRAE. Retinopathy severity, age, mean arterial blood pressure, duration of diabetes, glycosylated hemoglobin level, and body mass index were associated with CRVE. With the exception of glycosylated hemoglobin, similar factors were associated with AVR. Age (odds ratio [OR] per 10 years, 2.43 and 2.02) and retinopathy severity (OR per level, 1.14 and 1.21) were associated with focal retinal arteriolar narrowing and A/V nicking, respectively. In persons >/=18 years of age, smoking was associated with CRAE, CRVE, and A/V nicking (OR, 2.67), but not with AVR or focal arteriolar narrowing. CONCLUSIONS: This study documented the frequency and distribution of retinal vascular characteristics and their relationships to various factors in persons with type 1 diabetes.

Adult↗

PubMed2002

Testing model fit in longitudinal data analysis against alternatives with omitted covariates.

Several types of common model misspecifications can be re-formulated as problems of omitted covariates. These include situations with unmeasured confounders, measurement errors in observed covariates and informative censoring. Longitudinal data present special opportunities for detecting omitted covariates that are related to the observed ones differently across time than across individuals. This situation arises with period and cohort effects, as well as with usual formulations of classical measurement error in observed covariates. In this article we focus on testing for the existence of omitted covariates in longitudinal data analysis when models are fit by generalized estimation equations. When omitted covariates are present, specification of the correct link function conditionally on only observed covariates under the alternative usually involves complicated numerical integration. We propose a quasi-score test statistic that avoids the need to fit such alternative models. The statistic is asymptotically chi-square distributed under the null hypothesis of no omitted covariates with degrees of freedom determined by the assumed alternative structure. We study the significance level and the power of the quasi-score test in linear and logistic regression models. The test is then applied to an analysis of excessive daytime sleepiness.

Cohort Studies↗

PubMed2002

Bias adjustment in analysing longitudinal data with informative missingness.

The recent biostatistical literature contains a number of methods for handling the bias caused by 'informative censoring', which refers to drop-out from a longitudinal study after a number of visits scheduled at predetermined intervals. The same or related methods can be extended to situations where the missing pattern is intermittent. The pattern of missingness is often assumed to be related to the outcome through random effects which represent unmeasured individual characteristics such as health awareness. To date there is only limited experience with applying the methods for informative censoring in practice, mostly because of complicated modelling and difficult computations. In this paper, we propose an estimation method based on grouping the data. The proposed estimator is asymptotically unbiased in various situations under informative missingness. Several existing methods are reviewed and compared in simulation studies. We apply the methods to data from the Wisconsin Diabetes Registry Project, a longitudinal study tracking glycaemic control and acute and chronic complications from the diagnosis of type I diabetes.

Bias↗