Biomedical subjects

K Y Liang

Publications and source records attributed to K Y Liang.

At least 19 recordsLinked to original sources

PubMed1992

Vascular reactivity in young adults and cardiovascular disease. A prospective study.

Cardiovascular reactivity in response to the cold pressor test has been associated with an increased risk of coronary heart disease in middle-aged men. We studied 905 white male medical students, median age 22 years, in the Johns Hopkins Precursors Study. Systolic blood pressure, systolic blood pressure change during the cold pressor test, smoking, cholesterol, Quetelet index, and family history of coronary heart disease were measured on enrollment during 1948-1964. Incidence of cardiovascular morbidity and mortality was ascertained by annual questionnaires and death certificates. There was no association between change in systolic blood pressure during the cold pressor test, whether examined as a continuous variable or a 20 mm Hg or more rise, and the risk of subsequent cardiovascular disease or coronary heart disease. These findings did not change after adjustment for cardiovascular disease risk factors. Previously reported associations may have been due to preexisting arteriosclerosis, which increases the rise in systolic blood pressure during the cold pressor test. We conclude that cardiovascular reactivity to the cold pressor test in young adulthood is not a strong predictor of future cardiovascular disease.

Adult↗

PubMed1992

Risk factors in schizophrenia. Season of birth, gender, and familial risk.

The risk for schizophrenia among first-degree relatives of schizophrenic probands obtained from an epidemiological sample using family history methods was examined to determine whether month of birth of the proband was associated with familial risk. The results of this study of the first-degree relatives of 106 female schizophrenics and 275 male schizophrenics suggested that the relatives of probands born in the months February to May had the highest risk, although the association between month of birth and familial risk among the male probands was present only for those relatives who had onset of schizophrenia before the age of 30.

Adult↗

PubMed1992

Season of birth of siblings of schizophrenic patients.

The hypothesis that mothers of winter-spring-born schizophrenics have an unusual pattern of conception which results in an excess of winter-spring births was tested by studying the distribution of birth-dates of 401 siblings of 120 winter-spring-born schizophrenics and 157 siblings of 59 winter-spring-born controls. All analyses were gender-specific. The results suggest there is no association between the probability of a winter-spring date of birth and being a sibling of a winter-spring-born schizophrenic or control.

Adult↗

PubMed1992

Marginal models for correlated binary responses with multiple classes and multiple levels of nesting.

A model for correlated binary data is presented. Marginal probabilities and odds ratios are allowed to have general regression structures that include multiple classes and multiple levels of nesting. Estimation is done through the generalized estimating equations approach of Liang and Zeger (1986, Biometrika 73, 13-22). They are contrasted with conditional models and recommendations for choosing between the two are given. Examples from genetic epidemiology are presented.

Adult↗

PubMed1992

Efficacy of repeated measures in regression models with measurement error.

Ignoring measurement error may cause bias in the estimation of regression parameters. When the true covariates are unobservable, multiple imprecise measurements can be used in the analysis to correct for the associated bias. We suggest a simple estimating procedure that gives consistent estimates of regression parameters by using the repeated measurements with error. The relative Pitman efficiency of our estimator based on models with and without measurement error has been found to be a simple function of the number of replicates and the ratio of intra- to inter-variance of the true covariate. The procedure thus provides a guide for deciding the number of repeated measurements in the design stage. An example from a survey study is presented.

Biometry↗

PubMed1991

Incidence and risk factors for gout in white men.

OBJECTIVE: To identify potentially modifiable risk factors for the development of gout. DESIGN: Longitudinal cohort study (The Johns Hopkins Precursors Study). PARTICIPANTS: Of 1337 eligible medical students, 1271 (95%) received a standardized medical examination and questionnaire during medical school. The participants were predominantly male (91%), white (97%), and young (median age, 22 years) at cohort entry. OUTCOME MEASURE: The development of gout. RESULTS: Sixty cases of gout (47 primary and 13 secondary) were identified among 1216 men; none occurred among 121 women (P = .01). The cumulative incidence of all gout was 8.6% among men (95% confidence interval, 5.9% to 11.3%). Body mass index at age 35 years (P = .01), excessive weight gain (greater than 1.88 kg/m2) between cohort entry and age 35 years (P = .007), and development of hypertension (P = .004) were significant risk factors for all gout in univariate analysis. Multivariate Cox proportional hazards models confirmed the association of body mass index at age 35 years (relative risk [RR] = 1.12; P = .02), excessive weight gain (RR = 2.07; P = .02), and hypertension (RR = 3.26; P = .002) as risk factors for all gout. Hypertension, however, was not a significant risk factor for primary gout. CONCLUSIONS: Obesity, excessive weight gain in young adulthood, and hypertension are risk factors for the development of gout. Prevention of obesity and hypertension may decrease the incidence of and morbidity from gout; studies of weight reduction in the primary and secondary prevention of gout are indicated.

Adult↗

PubMed1991

Race, family income, and low birth weight.

The relations among race, family income, and low birth weight were examined using information obtained from the National Longitudinal Survey of Youth, which conducted yearly interviews with a nationally representative sample of young women identified in the late 1970s. Data were available for these women and their offspring from 1979 through 1988. Maternal education, maternal age, age/parity risk, marital status, and smoking during pregnancy served as covariates in cross-sectional and longitudinal analyses. The risk of low birth weight among births to black women and white women who were poor was at similarly high levels regardless of whether poverty was determined prior to study entrance or during the study period. Longitudinal analyses showed an exceptionally large increase in risk of low birth weight among children born to women whose prior pregnancy ended in a low-birth-weight infant. These two findings emphasize the importance of factors antecedent to the pregnancy in the genesis of low birth weight.

Adolescent↗

PubMed1991

Using log-linear models to test for associations among congenital malformations.

Log-linear models can be used to test for pairwise associations and higher order interactions among anatomically distinct birth defects or congenital malformations. A log-linear model, including terms for every possible pairwise association among seven severe and easily detectable congenital malformations, was examined using data on 16,217 infants registered in the Metropolitan Atlanta Congenital Defects Program between 1968 and 1986. The resulting model showed clear patterns of strong association between some congenital malformations and not others, and the presence of 3-way interaction terms where the association between two malformations depended on the presence of a third. Examining a more parsimonious log-linear model showed overlapping patterns of pairwise association involving anal-rectal atresia and omphalocele, anal-rectal atresia and limb deficiency, and anal-rectal atresia and tracheaesophageal fistula. A second common pattern involved a triangular cluster with a hierarchical relationship among the three malformations (where there was a strong association between the first and second malformations and between the first and third malformations, but the association between the second and third was only seen in the absence of the first). Three such overlapping triangular clusters were identified from these data: neural tube defects, oral clefts, and omphalocele; neural tube defects, oral clefts, and limb deficiency; and limb deficiency, diaphragmatic hernia, and neural tube defects.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities, Multiple↗

PubMed1991

Estimating effects of probands' characteristics on familial risk: I. Adjustment for censoring and correlated ages at onset.

Family studies with age at onset of the disease as the endpoint face two important problems: censoring and correlation of age at onset among relatives. We present a multivariate survival model for ages at onset of relatives which incorporates the problems cited above. The interpretations of regression coefficients and association parameter in the context of family studies are emphasized. The present paper describes a statistical method for estimating these parameters. In a companion paper [Pulver and Liang, Genet Epidemiol 8:339-350, 1991] this model is applied to a genetic epidemiologic study of schizophrenia.

Age Factors↗

PubMed1991

Estimating effects of proband characteristics on familial risk: II. The association between age at onset and familial risk in the Maryland schizophrenia sample.

In this report we apply methods outlined in the companion paper [Liang, Genet Epidemiol 8:329-338, 1991] to study the association between proband age at onset and familial risk among first-degree relatives of 374 schizophrenic probands. The analyses take into consideration the potential problems of censoring and correlation of age at onset within families. All analyses were done by gender of the proband; age at onset was dichotomized. The results of the analyses of the male probands suggest that there is an increased risk of schizophrenia among the relatives of male probands who have an onset prior to age 17 when compared to relatives of male probands who have an onset later than 16. We did not find an association between age at onset and familial risk among the female probands, but this may be due to the smaller number of female probands and the lower power associated with the analyses.

Adolescent↗

PubMed1991

Measuring familial aggregation by using odds-ratio regression models.

Detection of familial aggregation of a disease is important for studying possible genetic and environmental factors contributing to disease etiology. Accurate quantification of familial aggregation can provide guidance for subsequent, more sophisticated genetic studies. This article presents a statistical model and method for detecting both inter- and intra-class aggregation of a binary trait with family data. The method used here is based on the logistic regression model which incorporates effects of individual covariates while measuring familial aggregation of risk as the odds ratios among classes of relatives. An estimation equation approach is presented where the joint distribution of binary traits among family members need not be fully specified. Data from a genetic epidemiologic study on liver cancer in Shanghai are analyzed for illustration, and reveal strong aggregation of risk even after adjusting for covariates. Effects of non-random sampling and ascertainment bias are also discussed.

Adolescent↗

PubMed1991

Adjustment for non-differential misclassification error in the generalized linear model.

It is well known that estimates of association between an outcome variable and a set of categorical covariates, some of which are measured with misclassification, tend to be biased upon application of the usual methods of estimation that ignore the classification error. We propose a method to adjust for misclassification in covariates when one applies the generalized linear model. In the case where one can observe some true covariates only through surrogates, we combine a latent class analysis with the approach to incorporate multiple surrogates into the model. We include discussion on the efficacy of repeated measurements which one can view as a special case of multiple surrogates with identical distribution. We provide two examples to demonstrate the applicability of the method and the efficacy of multiple replicates for a covariate subject to misclassification in a regression framework.

Adolescent↗

PubMed1991

Effects of hepatitis B virus, alcohol drinking, cigarette smoking and familial tendency on hepatocellular carcinoma.

Independent and interactive effects related to the development of hepatocellular carcinoma were assessed using a community-based case-control study for hepatitis B virus, habitual alcohol drinking, cigarette smoking, peanut consumption and history of hepatocellular carcinoma among the immediate family. All 200 male newly diagnosed hepatocellular carcinoma patients were recruited consecutively through the period of study as the case group from two teaching medical centers in northern and southern Taiwan. Healthy community residents matched one-to-one with cases on age, sex, ethnic group and residential area were selected as the control group. The carrier status of HBsAg and HBeAg was determined by blind radioimmunoassays, and other risk factors were obtained through standardized interviews according to a structured questionnaire. Conditional logistic regression analysis showed a significant association between hepatocellular carcinoma and the carrier status of HBsAg and HBeAg with an odds ratio of 16.7 and 56.5, respectively, for carriers of HBsAg alone and for carriers of both HBsAg and HBeAg. There was a dose-response relationship between cigarette smoking and hepatocellular carcinoma with an odds ratio of 1.1, 1.5 and 2.6, respectively, for those who smoked 1 to 10, 11 to 20 and more than 20 cigarettes a day. A significant association with hepatocellular carcinoma was also observed for the habitual alcohol consumer with an odds ratio of 3.4. Those whose immediate family had a history of hepatocellular carcinoma were more likely to have the disease develop, with an odds ratio of 4.6. However, the frequency of peanut consumption was not significantly associated with hepatocellular carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

On estimating HLA/disease association with application to a study of aplastic anemia.

A multiplicative model is described relating HLA typing information to disease incidence. A likelihood-based method for estimating parameters in this model is proposed for use with data sets in which HLA haplotype information is available on a series of cases and their parents. This approach is extended to incorporate information from a matched control series for the purpose of estimating HLA and environmental risk factor effects simultaneously. The method is applied to data from aplastic anemia patients treated by bone marrow transplantation and the results are compared to unmatched case-control analyses using the same case series and several different control series.

Anemia, Aplastic↗

PubMed1990

The Cox proportional hazards model with change point: an epidemiologic application.

In this paper, we develop the Cox proportional hazards model with special structured time-dependent covariates in the context of prospective epidemiologic studies. Our model possesses the following two features: (i) different relative risk parameters are allowed for early versus late onset of the disease of interest; (ii) an additional parameter is introduced so that specification is not required for the time (age) at which a change of the magnitude of the relative risks takes place, the so-called change point. Some difficulties with statistical inference for the proposed model are briefly discussed, and the large-sample distribution of a test for no change point is derived. As an illustration, we apply the model to a set of data gathered on a group of white male medical students of The Johns Hopkins Medical School enrolled between 1948 and 1964. We examine the hypothesis that the effect of reactivity to the cold pressor test may vary with early versus late onset of hypertension.

Biometry↗

PubMed1990

The prediction of midlife coronary heart disease and hypertension in young adults: the Johns Hopkins multiple risk equations.

Educating medical students about the identification of risk factors for coronary disease and hypertension should be enhanced by exercises in which medical students identify their own risk factors and visualize the impact of current risk status on future risk of disease. A cohort of 1,130 former Johns Hopkins medical students were examined in medical school and followed annually from 1948 to 1964 to identify youthful factors associated with the development of coronary heart disease and hypertension in midlife. In the ensuing years through 1984, 51 cases of coronary heart disease and 114 cases of hypertension developed. Multiple risk equations using Cox proportional hazards regression were developed to predict these endpoints. Incidence of coronary heart disease was predicted best by an equation containing age, serum cholesterol at baseline, cigarette smoking at baseline, and paternal history of coronary disease. Hypertension was predicted best by an equation containing age, systolic blood pressure at baseline, paternal history of hypertension, and Quetelet index. These equations were applied to a class of present-day medical students to demonstrate the considerable variability in 30-year risk of coronary disease or hypertension. Thus, coronary heart disease and hypertension in midlife can be predicted by factors identified in youth. The Johns Hopkins multiple risk equations may be valuable as tools in preventive cardiology education to illustrate risk assessment and the importance of risk factor interventions.

Adult↗

PubMed1989

Predicting intrauterine growth retardation in sibships while considering maternal and infant covariates.

Data on 6,210 full-term sibships (gestational age greater than 36 weeks) reconstructed from birth certificates registered in Maryland between 1980 and 1984 were used to study sibship aggregation and recurrence risk of intrauterine growth retardation (IUGR) while considering maternal and infant covariates. In this study, IUGR was defined as being below the 10th percentile for race-, sex-, and gestational-age-specific birth weight based on all births registered in Maryland during 1984. Maternal factors (race, age at delivery, marital status, amount of prenatal care, concurrent illnesses, and complications during pregnancy) and infant factors (congenital malformations and first born child or not) were used as covariates in a modified logistic regression model which allowed correlation among sibs. First-time mothers who were under age 30 years, unmarried, received too little prenatal care, or had any reported pregnancy complications were at high risk of delivering an infant with IUGR. Even given the effects of these risk factors, however, there was a significant correlation in risk among full sibs (r = .237 +/- .028), which, combined with information on risk factors, can be used to estimate sibling recurrence risk for IUGR.

Adult↗

PubMed1989

Etiologic factors in renovascular fibromuscular dysplasia. A case-control study.

The role of several factors that have been suggested as being of etiologic importance in renovascular fibromuscular dysplasia was examined in a case-control study of 33 patients with angiographically demonstrated fibromuscular dysplasia and 61 renal transplant donor control subjects with normal renal arteries. The factors studied included use of oral contraceptive agents or markers of sex hormone dysfunction, mechanical stress to the renal artery wall, human lymphocytic antigen (HLA) type, cigarette smoking, history of hypertension for more than 5 years, and family history of cardiovascular disease. The risk of fibromuscular dysplasia was significantly (p = 0.003) increased (odds ratio = 4.1, 95% confidence interval = 1.5-10.9) among cigarette smokers. A significant (p less than 0.001) dose-response relation was noted between cigarette use and the risk of fibromuscular dysplasia developing (odds ratio = 8.6 for those who had smoked more than 10 pack-years). Personal history of hypertension more than 5 years was also associated (odds ratio = 5.0, 95% confidence interval = 1.1-22.8) with a significantly (p = 0.036) increased risk for the development of fibromuscular dysplasia. HLA-DRw6 antigen was more common in the 33 fibromuscular dysplasia patients than in the 61 renal transplant donor control subjects (odds ratio = 3.00, p = 0.067) or a second group of 934 ambulatory control subjects (odds ratio = 2.51, p = 0.031). Adjustment for cigarette smoking increased the odds ratio to 5.0 (95% confidence interval = 1.3-19.6). There was a positive though not statistically significant (odds ratio = 1.7, p = 0.175) association noted between family history of cardiovascular disease and fibromuscular dysplasia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗