Biomedical subjects

Heather J Litman

Publications and source records attributed to Heather J Litman.

6 recordsLinked to original sources

PubMed2007

Incorporating missingness for estimation of marginal regression models with multiple source predictors.

Multiple informant data refers to information obtained from different individuals or sources used to measure the same construct; for example, researchers might collect information regarding child psychopathology from the child's teacher and the child's parent. Frequently, studies with multiple informants have incomplete observations; in some cases the missingness of informants is substantial. We introduce a Maximum Likelihood (ML) technique to fit models with multiple informants as predictors that permits missingness in the predictors as well as the response. We provide closed form solutions when possible and analytically compare the ML technique to the existing Generalized Estimating Equations (GEE) approach. We demonstrate that the ML approach can be used to compare the effect of the informants on response without standardizing the data. Simulations incorporating missingness show that ML is more efficient than the existing GEE method. In the presence of MCAR missing data, we find through a simulation study that the ML approach is robust to a relatively extreme departure from the normality assumption. We implement both methods in a study investigating the association between physical activity and obesity with activity measured using multiple informants (children and their mothers).

Bias↗

PubMed2007

The effect of mode of delivery, parity, and birth weight on risk of urinary incontinence.

To examine the relationship between symptoms of urinary incontinence (UI) and mode of delivery, parity, and birth weight, data were obtained from a population-based random sample of 3,205 black, Hispanic, and white women age 30-79 in the Boston Area Community Health Survey. Measures include UI symptoms [>or=3 (moderate/severe) Sandvik's severity index]; reproductive history [live birth(s), no live births, never pregnant]; mode of delivery for live births (>or=1 vaginal birth, cesarean delivery only); parity (1, 2, >or=3); and maximum birth weight of live births (<4,000 g, >or=4,000 g). Using logistic regression, women having >or=1 vaginal delivery had twice the odds of UI compared to women with no pregnancies (P = 0.002) or only cesarean deliveries (P = 0.032). There was no difference in odds of UI between cesarean delivery only and never pregnant, by parity or birth weight. Vaginal delivery contributes to risk of UI for black, Hispanic, and white women.

Adult↗

PubMed2006

Prevalence of lower urinary tract symptoms and effect on quality of life in a racially and ethnically diverse random sample: the Boston Area Community Health (BACH) Survey.

BACKGROUND: Previous studies of lower urinary tract symptoms (LUTS) have focused on men, with few studies including minority populations. The Boston Area Community Health (BACH) Survey is designed to study the prevalence and impact of LUTS among both men and women in a racially, ethnically, and socioeconomically diverse population. METHODS: The BACH Survey used a stratified 2-stage cluster design to randomly sample 5506 adults aged 30 to 79 from the city of Boston, Mass (2301 men, 3205 women, 1770 blacks, 1877 Hispanics, and 1859 whites). Data were obtained using interviewer and self-administered questionnaires. The presence of LUTS was defined as an American Urological Association symptom index score of 8 or above. Quality of life was assessed using the Medical Outcomes Study 12-Item Short Form Survey (SF-12), and a measure of bother was based on the interference of urinary symptoms with various activities. Analyses were weighted to the Boston population using SUDAAN version 9.0 statistical software. RESULTS: The overall prevalence of LUTS was 18.7% and increased with age (10.5% at age 30-39 years to 25.5% at age 70-79 years) but did not differ by sex or race/ethnicity. Quality of life was significantly reduced among those with LUTS, as measured by the bother of symptoms and the SF-12 component scores. Prevalence of prescription medication use for urinary symptoms was low even among participants with LUTS, with more than 90% of participants reporting no medication use. CONCLUSIONS: In this population-based, racially and ethnically diverse random sample, LUTS were common among both men and women and increased substantially with age. Lower urinary tract symptoms had a negative impact on quality of life across age, sex, and race/ethnic groups.

Adult↗

PubMed2006

Serum androgen levels in black, Hispanic, and white men.

CONTEXT: Racial/ethnic differences in androgen levels could account for differences in prostate cancer risk, body composition, and bone loss. OBJECTIVE: The objective of the study was to investigate racial/ethnic variations in testosterone, bioavailable testosterone, dihydrotestosterone (DHT), SHBG, and dehydroepiandrosterone sulfate (DHEAS) levels. DESIGN: The Boston Area Community Health (BACH) Survey was a multistage stratified cluster random sample, recruiting from 2002 to 2005. SETTING: The study was a community-based sample of Boston. PARTICIPANTS: Participants included black, Hispanic, or white individuals, aged 30-79 yr, competent to sign informed consent and literate in English/Spanish. Of 2301 men recruited, 1899 provided blood samples (538 black, 651 Hispanic, 710 white). INTERVENTION: Intervention consisted of data obtained during in-person at-home interview, conducted by a bilingual phlebotomist/interviewer. MAIN OUTCOME MEASURE(S): Testosterone, bioavailable testosterone, DHT, DHT to testosterone ratio, SHBG, and DHEAS were measured. RESULTS: With or without adjustment for covariates, there were no significant differences in testosterone, bioavailable testosterone, or SHBG levels by race/ethnicity. DHEAS levels differed by race/ethnicity before covariate adjustment; after adjustment this difference was attenuated. Before adjustment, DHT and DHT to testosterone ratios did not significantly differ by racial/ethnic group. After adjustment, there was evidence of racial/ethnic differences in DHT (P = 0.047) and DHT to testosterone (P = 0.038) levels. Black men had higher DHT levels and DHT to testosterone ratios than white and Hispanic men. CONCLUSIONS: Because there are no racial/ethnic differences in testosterone levels, normative ranges need not be adjusted by race/ethnicity for androgen deficiency diagnosis for men aged 30-79 yr. Further investigation is needed to determine whether differences in DHT levels and DHT to testosterone ratio can help explain racial/ethnic variations in prostate cancer incidence, body composition, and bone mass.

Adult↗

PubMed2006

Marginal regression models with a time to event outcome and discrete multiple source predictors.

Information from multiple informants is frequently used to assess psychopathology. We consider marginal regression models with multiple informants as discrete predictors and a time to event outcome. We fit these models to data from the Stirling County Study; specifically, the models predict mortality from self report of psychiatric disorders and also predict mortality from physician report of psychiatric disorders. Previously, Horton et al. found little relationship between self and physician reports of psychopathology, but that the relationship of self report of psychopathology with mortality was similar to that of physician report of psychopathology with mortality. Generalized estimating equations (GEE) have been used to fit marginal models with multiple informant covariates; here we develop a maximum likelihood (ML) approach and show how it relates to the GEE approach. In a simple setting using a saturated model, the ML approach can be constructed to provide estimates that match those found using GEE. We extend the ML technique to consider multiple informant predictors with missingness and compare the method to using inverse probability weighted (IPW) GEE. Our simulation study illustrates that IPW GEE loses little efficiency compared with ML in the presence of monotone missingness. Our example data has non-monotone missingness; in this case, ML offers a modest decrease in variance compared with IPW GEE, particularly for estimating covariates in the marginal models. In more general settings, e.g., categorical predictors and piecewise exponential models, the likelihood parameters from the ML technique do not have the same interpretation as the GEE. Thus, the GEE is recommended to fit marginal models for its flexibility, ease of interpretation and comparable efficiency to ML in the presence of missing data.

Biometry↗

PubMed2004

Outcome for children with group III rhabdomyosarcoma treated with or without radiotherapy.

PURPOSE: To analyze the sites of relapse, relapse-free survival, and overall survival in children with Group III rhabdomyosarcoma treated with or without radiotherapy (RT). METHODS AND MATERIALS: The outcomes of 48 children with Group III rhabdomyosarcoma treated between 1980 and 1997 were evaluated. The median overall survival follow-up was 7.3 years. Of the 48 patients, 65% had embryonal histology. Local treatment after induction chemotherapy included complete surgical resection (CSR) alone in 9 (19%), CSR plus RT in 13 (27%), partial resection or rebiopsy plus RT in 10 (21%), and RT alone in 15 patients (31%). One child developed distant disease before completing local therapy. RESULTS: Of the 48 patients, 12 developed relapse at local (n = 3), regional (n = 4), or distant (n = 5) sites. All 9 patients treated with CSR after induction chemotherapy had embryonal/botryoid histology. Only 1 of these 9 patients developed relapse. No statistically significant difference was found in overall survival (p = 0.95) or relapse-free survival (p = 0.67) between patients treated with or without RT. The Kaplan-Meier estimate of 5-year overall survival and relapse-free survival was 76% +/- 7% and 74% +/- 7%, respectively. Significant predictors of relapse-free survival on univariate analysis included CSR (p = 0.03), nodal positivity (p = 0.001), and embryonal histology (p = 0.0003). On multivariate analysis, embryonal histology was the most significant predictor of relapse-free (p = 0.001) and overall (p = 0.01) survival. CONCLUSION: The overall survival for children with Group III rhabdomyosarcoma in this series was favorable. Embryonal/botryoid histology was the most significant predictor of both overall and relapse-free survival. We found that for a selected subgroup of children with embryonal histology, induction chemotherapy followed by complete surgical resection alone may be adequate local therapy.

Adolescent↗