Biomedical subjects

Bernardo Hernández

Publications and source records attributed to Bernardo Hernández.

11 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↗

PubMed2006

[The contribution of violence to maternal mortality in Morelos, Mexico].

OBJECTIVE: To document the under-registration of violent deaths related to pregnancy and the importance of considering these violent deaths within the definition of maternal mortality. MATERIAL AND METHODS: The study was carried out in the state of Morelos, based on the review of all death certificates (394) of reproductive aged women (12-49 years) who died during 2001. Based on a list of diagnostic criteria we eliminated 167 certificates that were neither violent deaths nor maternal deaths. The remaining 227 certificates were further evaluated through verbal autopsy and/or review of medical charts. RESULTS: Fifty-one violent deaths were found. Eighteen maternal deaths were officially reported in 2001, however, our study identified 23 direct maternal deaths and four violent deaths during pregnancy and the post-partum period. We found that this reproductive event was the direct trigger for the homicide or suicide of these four women, and only one of these cases was documented officially. CONCLUSIONS: Violent deaths related to pregnancy should be included in official maternal mortality statistics as indirect causes of maternal deaths. This would allow for a greater and more accurate understanding of violent maternal deaths and guide appropriate prevention and care policies, programs and services. Verbal autopsy is a useful technique for identifying cases of violent maternal deaths.

Adolescent↗

PubMed2005

Current wheezing, puberty, and obesity among mexican adolescent females and young women.

BACKGROUND: Studies suggest an association between obesity and asthma. This may be modified by the physiological changes of puberty. We aim to explore the relation between overweight and current asthma among Mexican adolescent females and young women and evaluate how puberty may modify this association. METHODS: Adolescent females (n=6944) and young women aged 11-24 years provided data. Current asthma was defined as wheezing in the last 12 months and obesity by body mass index (BMI). Puberty was defined by age at menarche. The association of obesity and current wheezing was evaluated by using logistic regression adjusting for confounders. The impact of puberty was studied by using stratified analysis by age at menarche. RESULTS: The prevalence of current wheezing was 16.2% (95% CI 15-17). Compared with girls of normal weight (BMI 15 to >or=85 percentile), obese girls (BMI>or=95 percentile) had an increased risk of current wheezing of 19% (OR=1.19; 95% CI 0.97-1.46). After stratifying by age at menarche, we observed that this increased risk was only present in girls with menarche at 11 years old or younger (1.31%; 95% CI 1.01-1.73). CONCLUSIONS: The association between obesity and asthma seems to be greater among girls with early puberty, suggesting the role of female hormones.

Adolescent↗

PubMed2005

Effect of urban vegetation on psychological restorativeness.

The present study analyzes the contribution which natural elements in the city make to restorativeness, that is, the potential of certain environments to help recover the capacity to focus attention, reduce mental fatigue, and reduce stress. We presented photographs of 12 urban scenes (streets, industrial areas, and buildings) with and without vegetation to 214 university students, divided into 12 groups who then completed the Perceived Restorativeness Scale. The results support the hypothesis, i.e., urban environments with natural elements yield higher restorativeness than urban environments lacking these.

Adolescent↗

PubMed2004

Support from a prenatal instructor during childbirth is associated with reduced rates of caesarean section in a Mexican study.

OBJECTIVE: to assess the association between non-clinical factors and the incidence of caesarean section (CS); to estimate the effect of a prenatal instructor's presence during childbirth on birth outcome (vaginal or CS). DESIGN: cross-sectional study from a register of women who attended prenatal classes. Multivariate logistic regression was used to measure the effects of each variable on whether the birth was vaginal or CS. SETTING: Mexico City, Mexico. PARTICIPANTS: 992 births to 847 women from the register of the Birth Education Centre (CEPAPAR) between 1987 and 2000. FINDINGS: the incidence of CS was 33%. The most commonly reported (by the women) reason for performing a CS was dystocia (53%). Most women were middle or upper-middle class professionals, and 85% of the women gave birth in private institutions. Odds of having a CS were higher among women who gave birth in a large hospital, women who were over 25 years of age, primigravidae, and women who were not supported by a prenatal instructor during childbirth. CONCLUSIONS: non-clinical factors considerably affect the type of birth outcome (vaginal vs. CS). A system in which a prenatal instructor provided support to the woman during childbirth could contribute significantly to reducing initial and repeat CS.

Adolescent↗

PubMed2004

Deaths from complications of unsafe abortion: misclassified second trimester deaths.

This study measured the contribution of abortion-related deaths to overall maternal mortality and calculated the underestimation of maternal mortality using verbal autopsy and clinical record review where available. We reviewed 807 death certificates of women aged 12-50 who died in 2001 in two sites of about 1.5 million inhabitants each in the state of Morelos (primarily rural) and the municipality of Nezahualcóyotl (primarily urban) in the state of Mexico. Deaths were classified as definite, possible or non-maternal deaths. Finally we identified abortion-related deaths and calculated the underestimation of maternal mortality. Among 326 possible maternal deaths, we encountered five misclassified cases: one spontaneous abortion and four non-abortion maternal deaths. Among 32 registered maternal deaths, we found four misclassified cases that were actually second trimester, abortion-related deaths. There were no officially registered abortion-related deaths in either Morelos or Nezahualcóyotl, making the overall underestimation of abortion mortality 100%. Abortion contributed 13.5% of all maternal deaths. The overall underestimation of maternal mortality was 13.55%, higher in Morelos (21.7%). There were no unregistered maternal deaths in Nezahualcóyotl. Unsafe abortion continues to be an important cause of maternal mortality, though first trimester deaths appear to be decreasing. We identified domestic violence as an important cause of death among pregnant and post-partum women, and two abortion-related suicides, and believe these should be reconsidered as indirect maternal deaths. The misclassification of second trimester abortion deaths as maternal deaths from other causes is an obstacle to preventing them.

Abortion, Induced↗

PubMed2003

Peak bone mineral area density and determinants among females aged 9 to 24 years in Mexico.

INTRODUCTION: Peak bone mineral area density is the amount of bone tissue present when skeletal maturation is completed. The exact age at which bone accumulation reaches a plateau varies with skeletal region. In Mexico and other Latin American countries, there are very few reports on bone mineral area density at early age. MATERIAL AND METHODS: A cross-sectional study of 461 females between 9 and 24 years of age in Cuernavaca, Mexico, distributed proportionately by age group, determined the bone mineral density (BMD) in femur, lumbar spine, and subcranial skeleton, using a Hologic 4500-Series A osteodensitometer. The peak bone mineral area density (PBM) was determined by using the sigmoid growth model defined by Raymond-Pearl (CSRP). Cohort comparisons among different age groups were developed to evaluate BMD in three skeletal regions, with the Dunnett test, comparing the slopes of BMD by each age stratum. Also, the primary determinants of BMD were evaluated through models of multiple linear regression. RESULTS: The timing of PBM is highly site specific with some skeletal regions reaching PBM earlier: beginning with the femur, and later reaching the lumbar spine and subcranial skeleton. Using a multivariate model, age and body weight were important predictors of BMD in the three anatomical regions studied ( p<.001). The percentage of fat is associated in an inversely proportionate manner ( p<.005), as independent predictors for BMD in the lumbar spine. The age of the onset of menstruation is also a predictor of BMD in the lumbar spine ( p<0.05); vigorous activity is an important predictor in the subcranial skeleton ( p<0.001). DISCUSSION: For Mexican females in the state of Morelos, the BMD are similar to that reported in a number of ethnic groups. In mestizo females the timing of PBM is highly site specific with some skeletal regions acquiring PBM earlier: specifically, in the femoral region where PBM rapidly reached a plateau. In Mexico, early strategies for preventing osteoporosis should be focused on promoting physical activity and appropriate eating habits (control of obesity, among others) during the puberty stage.

Adipose Tissue↗

PubMed2003

Factors associated with overweight and obesity in Mexican school-age children: results from the National Nutrition Survey 1999.

OBJECTIVE: The objective of the study was to measure the prevalence of overweight and obesity in Mexican school-age children (5-11 years) in the National Nutrition Survey 1999 (NNS-1999). MATERIAL AND METHODS: Overweight and obesity (defined as an excess of adipose tissue in the body) were evaluated through the Body Mass Index (BMI) in 10,901 children, using the standard proposed by the International Obesity Task Force. Sociodemographic variables were obtained using a questionnaire administered to the children's mothers. RESULTS: The national prevalence of overweight and obesity was reported to be 19.5%. The highest prevalence figures were found in Mexico City (26.6%) and the North region (25.6%). When adjusting by region, rural or urban area, sex, maternal schooling, socioeconomic status, indigenous ethnicity and age, the highest prevalences of overweight and obesity were found among girls. The risks of overweight and obesity were positively associated with maternal schooling, children's age and socioeconomic status. CONCLUSIONS: Overweight and obesity are prevalent health problems in Mexican school-age children, particularly among girls, and positively associated with socioeconomic status, age, and maternal schooling. This is a major public health problem requiring preventive interventions to avoid future health consequences. The English version of this paper is available too at: http://www.insp.mx/salud/index.html.

Child↗

PubMed2003

[Factors associated with physical activity among Mexican women of childbearing age].

OBJECTIVE: To document the practice of light and heavy physical activities, especially sports and exercise, among women from 12 to 49 years old in Mexico, and to evaluate the association that that has with some sociodemographic characteristics. METHODS: A sample of 2 367 women 12 to 49 years old living in Mexico in 1999 was studied through secondary analysis of data from Mexico's 1999 National Nutrition Survey (Encuesta Nacional de Nutrición). The Survey used a clustered stratified multistage sampling scheme, with a final sample of 21 000 homes in the entire country. A questionnaire was used to evaluate the time that the women spent on various forms of physical activity, with the activity measured on a scoring scale in terms of metabolic equivalents (METs). The dependent variables in the study were the time spent on heavy physical activities (those that require an energy expenditure of at least 5 METs/hour) and the time devoted to light or sedentary activities (such as sitting while on the job or elsewhere; watching television, a video, a movie, or a theater presentation; or sleeping). The independent variables were age, schooling, parity, region of the country, area of residence (urban or rural), socioeconomic level (measured through an index prepared based on housing conditions and household possessions), and marital status. The association between the independent variables and practicing sports was evaluated, and gross odds ratios (ORs) were calculated, with 95% confidence intervals (CIs). In order to identify the association between practicing sports and the independent variables a logistic regression model was used, adjusted for the effects of possible confounding variables. Adjustments were also made in the probability of a woman's being selected for the sample, using a weighting factor. In addition, adjustments were made to control for the design effect produced by the grouping of the observations in the sample, using the "svy" complex-samples routine of the Stata version 7.0 statistical analysis computer software. RESULTS: The 2 367 women whose information was analyzed spent an average of 0.08 hours per day practicing sports and 1.25 hours per day on heavy physical activities. Only 16% of the women reported that they regularly practiced some sport. After adjusting for all the independent variables, the women older than 30 years had a lower OR of practicing sports in comparison to women who were 20 years of age or less (OR = 0.53; 95% CI: 0.33 to 0.84), as was also true for women 21-30 years old (OR = 0.35; 95% CI: 0.23 to 0.54). Having the highest level of schooling and not having had children were both directly associated with practicing a sport. While the area of residence (urban or rural), marital status, and socioeconomic level showed differences among the groups, such differences were not significant after adjusting for the other study variables. In terms of physical activity measured in METs, the time spent on sports made up 10% of the total for heavy activity and 0.7% of the overall total. In terms of the possibility of being among the 10% of the women who expended the fewest METs per day, that was more likely for women under 21 years of age than it was for women 31 or older, and it was also more likely for women who had a primary level of schooling than for women with a secondary education. CONCLUSIONS: This study showed that practicing sports is not a frequent form of physical activity among women of childbearing age in Mexico, especially those who are over 20 years of age and those with a low level of schooling. This situation could contribute to increases in the prevalence of obesity and chronic diseases.

Adolescent↗

PubMed2002

Attachment to the physical dimension of places.

Social relationships had been important in explanation and prediction of attachment to places. Although some have asserted the importance of physical aspects of the environment in the formation of attachment ties to a place, the social environment is required for the formation of bonds to a place, although strong emphasis on the social aspect has been questioned and the importance of the physical environment noted. The present objective in two studies was to test whether college students (ns = 30 and 27) show a preference for a place they know, independently of the social interactions developed in them. Results confirmed the hypothesis, i.e., after a very brief stay in a certain place with nobody else there, these college students preferred that place to another with which they had not had previous contact.

Adolescent↗

PubMedDate not supplied

Chronic disease risk factors among healthy adolescents attending public schools in the state of Morelos, Mexico.

BACKGROUND: Little research (and fewer interventions) has been done on longitudinal exposure to risk factors for chronic diseases in young people in Latin America, including Mexico, although chronic diseases constitute the first cause of death in Mexico. Our objective was to document the prevalence of chronic disease risk factors among adolescents as a baseline measurement for a cohort study and to develop educational interventions. METHODS: Questionnaires, blood samples, and anthropometric measurements were collected from 13,293 public school students of both sexes, ages 11-24 years in Morelos, Mexico. This constitutes the baseline measurement for a cohort study. Twenty focus groups and 10 in-depth interviews were done with girls aged 12-17 years. Two educational interventions promoting physical activity and sexual health were designed. RESULTS: Prevalence of obesity was 21.2%. On average, participants spent 0.5 h/day on vigorous physical activity and 3.7 h/day watching television. Sexual initiation was reported by 14.5% (girls = 9.1%, boys = 21.5%); 52.3% of whom reported using condoms. Young women demonstrated correct condom use and perceived themselves at risk for HIV/AIDS but did not have condom negotiation skills. Prevalence of experimenting with tobacco was 15.1% (girls = 10.4%, boys = 21.1%); current smoking was 14.4% (girls = 10.6%) and boys = 19.2%), while 6.3% of participants reported monthly intoxication with alcohol, and 4.5% reported past and 2.1% reported current illegal drug use. CONCLUSIONS: Results indicate substantial exposure to risk factors for chronic diseases and reproductive health problems in this population. The study will generate interventions and constitutes initiation of a longitudinal study able to explore causal associations between risk factors and chronic diseases in this population.

Adolescent↗