[Show abstract][Hide abstract] ABSTRACT: Students in statistics service courses are frequently exposed to dogmatic approaches for evaluating the role of randomization in statistical designs, and inferential data analysis in experimental, observational and survey studies. In order to provide an overview for understanding the inference process, in this work some key statistical concepts in probabilistic and nonprobabilistic sampling are discussed. The statistical model constituting the basis of statistical inference is postulated and a brief review of the finite population descriptive inference and a quota sampling inferential theory are provided. Some comments on distinct approaches for conducting inferences in probabilistic and nonprobabilistic samples are adduced.
International Journal of Mathematical Education 11/2010; November 01(2002):819-828.
[Show abstract][Hide abstract] ABSTRACT: In this work simultaneous confidence intervals for the variance components in the two-way balanced crossed random effects model with interaction have been derived under the usual assumptions of normality and independence of random effects. The intervals are conservative in the sense that the true confidence coefficient is as large as preassigned value. The formulas are illustrated using published data with SAS outputs.
[Show abstract][Hide abstract] ABSTRACT: Drug users have been found to be at high risk of mortality but the mortality experience of Hispanic drug users remains understudied. This study assessed mortality among Puerto Rican injection drug users (IDUs) in New York City (NY), and in Puerto Rico (PR). Study subjects were 637 IDUs from NY and 319 IDUs from PR. Mortality was ascertained using data from the National Death Index. Annual mortality rate of the NY cohort was 1.3 per 100 person years compared to the PR cohort with a rate of 4.8. Compared to the Hispanic population of New York City, the standardized mortality ratio (SMR) of the NY cohort was 4.4. Compared to the population of Puerto Rico, the SMR of the PR cohort was 16.2. The four principal causes of death were: NY-HIV/AIDS (50.0%), drug overdoses (13.3%), cardiovascular conditions (13.3%), and pulmonary conditions (10.0%); PR-HIV/AIDS (37.0%), drug overdoses (24.1%), sepsis (13.0%), and homicide (11.1%). Modeling time to death using Cox proportional hazards regression, the relative risk of mortality of the PR cohort as compared to the NY cohort was 9.2. The other covariates found to be significantly associated with time to death were age, gender, education, social isolation, intoxication with alcohol, and HIV seropositivity. The large disparity in mortality rates found in this study suggests that health disparities research should be expanded to identify intra-group disparities. Furthermore, these results point to an urgent need to reduce excess mortality among IDUs in Puerto Rico.
Journal of Urban Health 12/2006; 83(6):1114-26. · 1.89 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper reports findings on 334 out-of-treatment drug users in Puerto Rico and 617 in New York City, at the 6-month follow-up interview of a Longitudinal Survey. Main outcomes were health care and drug treatment utilization since baseline, assessed by asking participants if they had received physical or mental health services (including HIV medications), and if they had been in methadone maintenance, inpatient or outpatient drug treatment, or drug treatment while incarcerated. Chi-square tests were used to evaluate associations between gender and the various correlates. Logistic regression was used to calculate the contribution of each variable in predicting use of drug treatment. The analysis suggests that women in both sites were likely to suffer from disparities in both health care and drug treatment utilization when compared with men, albeit women in New York utilized more drug treatment resources and were more embedded in the immediate family than their female peers in Puerto Rico. Further research to specify the impact of contextual factors at the organizational and community levels, among members of the same ethnic group residing in different sites, may prove valuable in identifying the health needs and the factors that impede or facilitate drug-using women in obtaining the most appropriate treatment. Findings from these studies can help in developing appropriate public health policy and science-based drug treatment programs to eliminate disparities such as the ones detected in this study.
Health Policy 02/2006; 75(2):159-69. · 1.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study examined factors associated with drug treatment dropout among injection drug users (IDUs) in Puerto Rico, a group that has contributed significantly to the self-sustaining AIDS epidemic in the island since the mid-1980s. A total of 557 IDUs were recruited from communities in a semirural region of Puerto Rico, as part of a longitudinal study testing the efficacy of a two-facet intervention model, based on motivational interviewing. Of 124 IDUs who had entered drug treatment at follow-up, 33 (26.6%) dropped out before completing all recommended sessions. Multiple logistic regression analysis showed that age, homelessness, and speedball use were significantly associated with drug treatment dropout. Conversely, participants who received the two-facet intervention were significantly less likely to drop out of drug treatment. Receiving psychiatric services also reduced the odds of treatment dropout. Improving adherence to drug treatment and reducing dropout rates are complex processes that need to be addressed at the individual behavioral and social support levels, as well as the program process and resource levels.
[Show abstract][Hide abstract] ABSTRACT: This paper reports results of an analysis of the association between alcohol intoxication and injection and sexual HIV risk behaviors among 557 Hispanic heroin and cocaine injectors, not in treatment, who were recruited in poor communities in Puerto Rico. Subjects were part of a longitudinal prevention-intervention study aimed at reducing drug use and HIV risk behaviors. Participants reported a high prevalence of co-occurring conditions, particularly symptoms of severe depression (52%) and severe anxiety (37%), measured by Beck's Depression Index and Beck's Anxiety Index, respectively. Alcohol intoxication during the last 30 days was reported by 18% of participants. Associations were found between alcohol intoxication and both injection and sexual risk behaviors. In the bivariate analysis, subjects reporting alcohol intoxication were more likely to inject three or more times per day, pool money to buy drugs, share needles, and share cotton. They were also significantly more likely to have a casual or paying sex partner and to have unprotected sex with these partners. After adjustment, sharing needles and cotton, having sex with a paying partner or casual partner, and exchanging sex for money or drugs were significantly related to alcohol intoxication. HIV prevention programs, to be effective, must address alcohol intoxication and its relation to injection and sexual risk behaviors as a central issue in HIV prevention among drug injectors.
Drug and Alcohol Dependence 01/2005; 76(3):229-34. · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study examined the effectiveness of a combined counseling and case management behavioral intervention, using motivational interviewing strategies, in engaging Hispanic injection drug users in treatment and reducing drug use and injection-related HIV risk behaviors. Follow up data are presented on 440 (79.0%) of 557 randomized participants, 6 months after the initial interview. Subjects in the experimental arm were significantly less likely to continue drug injection independent of entering drug treatment, and were also more likely to enter drug treatment. Subjects in both arms who entered drug treatment were less likely to continue drug injection. Among subjects who continued drug injection, those in the experimental arm were significantly less likely to share needles. Confirming the outcomes of this study in other Hispanic sites and populations could be a critical step towards reducing factors that contribute to the self-sustaining HIV/AIDS epidemic in Puerto Rico and communities in the U.S. mainland.
[Show abstract][Hide abstract] ABSTRACT: This paper assesses mortality rate for a cohort of drug users in Puerto Rico compared with that of the Island's general population, examining causes of death and estimating relative risk of death. Date and cause of death were obtained from death certificates during 1998. Vital status was confirmed through contact with subjects, family, and friends. HIV/AIDS was the major cause of death (47.7%), followed by homicide (14.6%), and accidental poisoning (6.3%). Females had higher relative risk of death than males in all age categories. Not living with a sex partner and not receiving drug treatment were related to higher mortality due to HIV/AIDS. Drug injection was the only variable explaining relative risk of death due to overdose. Puerto Rico needs to continue developing programs to prevent HIV/AIDS among drug users. Special attention should be given to young women, who appear to be in greatest need of programs to prevent early mortality.
Puerto Rico health sciences journal 01/2004; 22(4):369-76. · 0.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study was conducted to identify factors accounting for differences in health care and drug treatment utilization between Puerto Rican drug users residing in 2 separate locations. Survey findings from 334 drug users in Puerto Rico and 617 in New York City showed that those in Puerto Rico were 6 times less likely than their counterparts in New York to have used inpatient medical services and 13 to 14 times less likely to have used outpatient medical services or methadone. They also were less likely to have health insurance or past drug treatment. After site was controlled for, health insurance and previous use of physical or mental health services remained significant predictors of health care and drug treatment utilization during the study period. Although Puerto Rican drug users in Puerto Rico are not an ethnic minority, they reported significant disparities in health services use compared with Puerto Rican drug users in New York.
[Show abstract][Hide abstract] ABSTRACT: It is known that vitamin C status is compromised in smokers. The vitamin C status of nonsmokers who are exposed to environmental tobacco smoke (ETS) is now being elucidated.
We assessed vitamin C status in children who were either exposed or not exposed to ETS, and we sought to associate changes in vitamin C status with the amount of ETS exposure.
The study group included 512 children aged 2-12 y; 50% of them were exposed to ETS in the home because their parents smoked. Dietary intake of vitamin C, obtained with a 24-h recall questionnaire, and blood ascorbate concentrations were compared in the exposed and unexposed groups. Smoke exposure was assessed by measuring a biomarker, urinary cotinine. Age, sex, and body mass index were examined as potential correlates of vitamin C status in each exposure category.
Plasma ascorbate concentrations were lower, by 3.2 micro mol/L on average, in ETS-exposed children than in unexposed children who consumed equivalent amounts of vitamin C; this was a highly significant difference (P = 0.002). This reduction in plasma ascorbate occurred even with very low exposure to ETS.
ETS can reduce concentrations of ascorbate, an important blood antioxidant, even when the amount of smoke exposure is minimal. Children exposed to ETS should be encouraged to consume increased amounts of foods rich in vitamin C or should be given the equivalent amount of this vitamin as a supplement.
American Journal of Clinical Nutrition 02/2003; 77(1):167-72. · 6.50 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of a project-based approach for designing a one-year graduate level programme in applied statistics is addressed. The pedagogical approach, academic setting, and learning activities are described in a multidisciplinary context. Some comments on implementation of such a programme based on the results from five successive graduating classes at the University of Veracruz (1994–2000) are included.
International Journal of Mathematical Education 01/2003; 34(1):57-63.
[Show abstract][Hide abstract] ABSTRACT: The extent to which underreporting of drug use in household surveys affects the validity of epidemiological studies of drug use disorders is largely unknown. We developed a list of known hard core drug users as part of a larger household study in Puerto Rico. The known drug users were recruited and interviewed with the same procedures used for the respondents selected through area-probability sampling. Upon completion of the interview, subjects were asked to provide a sample of scalp hair. A total of 78 hair specimens were collected from the known drug users. Hair specimens were screened for cocaine and heroin using radio immunoassay, and confirmed using gas chromatography/mass spectrometry. Using the cutoff of 0.2 ng/mg of hair, 93.2% of the hair specimens were classified positive for cocaine and 75.7% for heroin. With the hair test results as the gold-standard, we calculated specificity and sensitivity statistics as measures of the validity of self-reports. Self-reports of drug use in the past 3 months had a specificity of 78% or higher for both drugs. The sensitivity of self-reports was 69.6% for reports of recent cocaine use and 78.6% for reports of recent heroin use. Sensitivity increased with reports of use in more remote time periods, among subjects reporting DSM-IV drug disorder symptoms, and among those reporting use of both drugs. The results suggest that while drug reports of hard core drug users interviewed in household surveys might be more valid than those of the general population, there still remains considerable under-reporting.
Drug and Alcohol Dependence 09/2002; 67(3):269-79. · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Despite the widespread use of household surveys to assess the epidemiology of illicit drug use and abuse, there is very little information about the willingness of respondents to disclose their use of drugs in household studies outside the US.
As part of a household study of substance use disorders in Puerto Rico, we collected hair specimens from a sub-sample of 114 respondents. Hair specimens were screened using a radio immunoassay. Screened-positive specimens were confirmed using gas chromatography/mass spectrometry.
Using hair-test results as the standard, specificity of self-reports was 98% or higher for both drugs. The sensitivity of all self-reports was low, although lifetime use reports had somewhat higher sensitivities. The sensitivity of self-reports of recent cocaine use was particularly low, 7.1%. The sensitivity of heroin use reports was somewhat higher, 33.3% for recent use and 66.7% for lifetime use. The estimate of recent cocaine use based on hair tests was 13.7 times the estimate generated from interview reports. For heroin use, the test-based estimate was 2.9 times the rate generated from the interview reports. A shift from the cut-off level of 0.2 ng/mg to 0.5 ng/mg had only a marginal improvement on validity, with sensitivity increasing from 7.1% to 11.1% for self-reported recent cocaine use.
The results suggest that drug users, for the most part, are not willing to disclose their use of drugs in household surveys in Puerto Rico. Methods to increase the willingness of respondents to disclose their use of drugs are needed.
International Journal of Epidemiology 11/2001; 30(5):1042-9. · 6.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Frequency of injection has been consistently found to be higher among Puerto Rican Injection drug users (IDUs) than among other groups of IDUs. Several explanations have been suggested, but an empirical explanation has yet to be presented. This study compares the frequency of injection of Puerto Rican IDUs in East Harlem, New York, with that of IDUs in Bayamon, Puerto Rico. Study subjects comprised 521 Puerto Rican IDUs from East Harlem and 303 IDUs from Bayamon. The mean frequency of injection among IDUs in East Harlem was 2.8, the corresponding mean in Bayamon was 5.4. Younger IDUs reported a higher number of daily injection episodes than older IDUs, and the IDU group in Bayamon was 5 years younger than the group in East Harlem. The drug use variables accounted for a greater portion of the between-city difference than the demographic and psychosocial variables. Use of noninjected drugs, as well as the use of prescribed methadone, were found to be associated with a lower number of daily injections. Conversely, injection of cocaine, injection of cocaine mixed with heroin ("speedball"), and injection of larger amounts of drug solution were found to be associated with a higher number of daily injections.
(C) 2001 Lippincott Williams & Wilkins, Inc.
[Show abstract][Hide abstract] ABSTRACT: This study was designed to determine among various personal, socioeconomic, and environmental factors those which had the greatest influence on exposure to environmental tobacco smoke (ETS) in a population of children residing in a tropical environment and to compare these results with those obtained in the literature of tobacco exposed children in temperate climates. Urine specimens were collected from 606 healthy Puerto Rican children (2-12 years) living in an industrial area and analyzed for cotinine, a quantitative biomarker for exposure to ETS. Parents completed a questionnaire covering smoking habits and socioeconomic information. Seventy per cent of the children were reported to be exposed to ETS, 50% resulting from exposure to smoke from either or both parents. Major determinants to ETS exposure were found to be presence of smoker, number of smokers, identity of smoker, number of cigarettes smoked in the household and child age with the youngest children suffering twice the exposure of older children. Non-determinants were exposure to smoke other than from the parent, sex of the child, season of the year and several socioeconomic factors including civil and employment status of the mother, mother's age and educational background and whether food stamps were being received. Results of a multiple regression analysis showed that our predictors accounted for 40% of cotinine appearing in the urine. Reasons for this relatively low value may be due in part to precision of our analytic method and lower levels of ambient smoke in our population vs. others that reported higher R(2) values. Predictions from questionnaire information for high ETS exposure were not always the same as those indicated by urinary cotinine emphasizing that the bioindicator, which indicates the actual inhalation of ETS, is a better predictor of exposure than responses from a questionnaire.
Nicotine & Tobacco Research 03/2001; 3(1):61-70. · 2.48 Impact Factor