Aluísio J. D. Barros

Alternatives for logistic regression in cross-sectional studies: an empirical comparison of models that directly estimate the prevalence ratio.

BackgroundCross-sectional studies with binary outcomes analyzed by logistic regression are frequent in the epidemiological literature. However, the odds ratio can importantly overestimate the prevalence ratio, the measure of choice in these studies. Also, controlling for confounding is not equivalent for the two measures. In this paper we explore alternatives for modeling data of such studies with techniques that directly estimate the prevalence ratio.MethodsWe compared Cox regression with constant time at risk, Poisson regression and log-binomial regression against the standard Mantel-Haenszel estimators. Models with robust variance estimators in Cox and Poisson regressions and variance corrected by the scale parameter in Poisson regression were also evaluated.ResultsThree outcomes, from a cross-sectional study carried out in Pelotas, Brazil, with different levels of prevalence were explored: weight-for-age deficit (4%), asthma (31%) and mother in a paid job (52%). Unadjusted Cox/Poisson regression and Poisson regression with scale parameter adjusted by deviance performed worst in terms of interval estimates. Poisson regression with scale parameter adjusted by χ2 showed variable performance depending on the outcome prevalence. Cox/Poisson regression with robust variance, and log-binomial regression performed equally well when the model was correctly specified.ConclusionsCox or Poisson regression with robust variance and log-binomial regression provide correct estimates and are a better alternative for the analysis of cross-sectional studies with binary outcomes than logistic regression, since the prevalence ratio is more interpretable and easier to communicate to non-specialists than the odds ratio. However, precautions are needed to avoid estimation problems in specific situations.

Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect

The importance of breastfeeding in low-income and middle-income countries is well recognised, but less consensus exists about its importance in high-income countries. In low-income and middle-income countries, only 37% of children younger than 6 months of age are exclusively breastfed. With few exceptions, breastfeeding duration is shorter in high-income countries than in those that are resource-poor. Our meta-analyses indicate protection against child infections and malocclusion, increases in intelligence, and probable reductions in overweight and diabetes. We did not find associations with allergic disorders such as asthma or with blood pressure or cholesterol, and we noted an increase in tooth decay with longer periods of breastfeeding. For nursing women, breastfeeding gave protection against breast cancer and it improved birth spacing, and it might also protect against ovarian cancer and type 2 diabetes. The scaling up of breastfeeding to a near universal level could prevent 823,000 annual deaths in children younger than 5 years and 20,000 annual deaths from breast cancer. Recent epidemiological and biological findings from during the past decade expand on the known benefits of breastfeeding for women and children, whether they are rich or poor.

The challenge of reducing neonatal mortality in middle-income countries: findings from three Brazilian birth cohorts in 1982, 1993, and 2004

BACKGROUND Middle-income countries will need to drastically reduce neonatal deaths to achieve the Millennium Development Goal for child survival. The evolution of antenatal and perinatal care indicators in the Brazilian city of Pelotas from 1982 to 2004 provides a useful case study of potential challenges. METHODS We prospectively studied three birth cohorts representing all urban births in 1982, 1993, and from January to July, 2004. The same methods were used in all three studies. FINDINGS Despite improvements in maternal characteristics, prevalence of preterm births increased from 6.3% (294 of 4665) in 1982 to 16.2% (342 of 2112) in 2004, corresponding to a 47 g reduction in mean birthweight. Average number of antenatal visits in 2004 was 8.3 per woman, but quality of care was still inadequate--97% of women had an ultrasound scan, but only 1830 (77%) had a vaginal examination and 559 of 1748 non-immunised women did not receive tetanus toxoid. Rate of caesarean sections increased greatly, from 28% (1632 of 5914) in 1982 to 43% (1039 of 2403) in 2004, reaching 374 of 456 (82%) of all private deliveries in 2004. The increased rate of preterm births seemed to result largely from caesarean sections or inductions. Newborn care improved, and gestational-age-specific mortality rates had fallen by about 50% since 1982. As a result, neonatal mortality rates had been stable since 1990, despite the increase in preterm deliveries. INTERPRETATION Excessive medicalisation--including labour induction, caesarean sections, and inaccurate ultrasound scans--led by an unregulated private sector with spill-over effects to the public sector, might offset the gains resulting from improved maternal health and newborn survival. These challenges will have to be faced by middle-income countries striving to achieve the child survival Millennium Development Goal.

The Role of Perceived Personal Barriers to Engagement in Leisure-Time Physical Activity

OBJECTIVES We sought to identify perceived personal barriers to physical activity and examine the potential association between these barriers and sociodemographic and behavioral variables, including participation in leisure-time physical activity. METHODS In 2003, we conducted a population-based study in Pelotas, Brazil. Participants aged 20 years and older were selected according to a multistage sampling strategy. Participants responded to both the International Physical Activity Questionnaire and a standardized questionnaire investigating 8 perceived personal barriers. RESULTS Only 26.8% of participants achieved 150 minutes per week of leisure-time physical activity. Lack of money (40.3%) and feeling too tired (38.1%) were the most frequently reported barriers to physical activity. A dose-response group association was observed between number of perceived barriers and level of physical activity. In the multivariable analysis, lack of time, dislike of exercising, feeling too tired, lack of company, and lack of money were associated with physical inactivity. CONCLUSION Detection of the determinants of physical inactivity, a growing epidemic, should be a public health priority. Brazil is a middle-income (developing) country. The prevalence of most of the personal barriers studied was higher in this population than those levels observed in high-income (developed) countries. Perceiving 5 of the 8 barriers investigated was inversely associated with leisure-time physical activity level.

Bioelectrical impedance analysis in clinical practice: a new perspective on its use beyond body composition equations

Purpose of reviewThe bioelectrical impedance analysis is not a direct method for estimating body composition. Its accuracy depends on regression equations, and recent papers have suggested that this approach should not be used in several clinical situations. Another option is to obtain information about the electrical properties of tissues by using raw bioelectrical impedance measurements, resistance and reactance. They can be expressed as a ratio (phase angle) or as a plot (bioelectrical impedance vector analysis). This review describes their use in clinical practice. Recent findingsThe phase angle changes with sex and age. It is described as a prognostic tool in many clinical situations. There are some controversies about considering it as a nutritional marker. Studies in burn victims and sickle-cell disease corroborate its ability to evaluate cell membrane function. Bioelectrical impedance vector analysis allows a semi-quantitative estimation of body composition from information from tissue hydration and soft-tissue mass in a plot. It can be used in healthy individuals or patients, for a population or individual evaluation of fluid imbalance or an assessment of soft-tissue mass. It has also been used as a prognostic tool in dialysis and cancer patients. SummaryThe phase angle can be considered a global marker of health, and future studies are needed to prove its utility in intervention studies. Bioelectrical impedance vector analysis has increased its utility in clinical practice, even when the equations may be inaccurate for body composition analysis.

Desigualdades na utilização e no acesso a serviços odontológicos: uma avaliação em nível nacional

Para avaliar a situacao de utilizacao e acesso aos servicos de odontologia no Brasil e estudar diferenciais entre os estratos socioeconomicos, utilizaram-se dados da Pesquisa Nacional por Amostragem de Domicilios (PNAD) de 1998, realizada pelo IBGE. A analise, que levou em conta o desenho amostral, indicou um nivel baixo de utilizacao de servicos odontologicos. Setenta e sete por cento das criancas de 0-6 anos e 4% dos adultos de 20-49 anos nunca haviam consultado um dentista. Entre estes adultos, comparando-se os 20% mais pobres com os 20% mais ricos, observou-se que o numero de desassistidos era 16 vezes maior entre os primeiros. No grupo de 0-6 anos, as criancas ricas consultaram o dentista cinco vezes mais do que as pobres no ano anterior a entrevista. Cerca de 4% dos que procuraram atendimento odontologico nao o obtiveram, 8% dos quais entre os mais pobres e 1% entre os mais ricos. A maioria (68%) dos atendimentos do grupo mais pobre foi financiada pelo SUS, enquanto 63% deles foram pagos pelos mais ricos. As maiores desigualdades no acesso e na utilizacao de servicos odontologicos foram encontradas, exatamente, nos grupos de menor acesso ou utilizacao. A participacao do SUS nos atendimentos odontologicos e muito mais baixa do que na atencao medica.

Indicador econômico para o Brasil baseado no censo demográfico de 2000

OBJETIVO: Propor um indicador economico para o Brasil baseado em bens de consumo usando variaveis presentes no censo demografico de 2000. METODOS: O indicador, denominado Indicador Economico Nacional (IEN), foi desenvolvido a partir de 12 bens e a escolaridade do chefe de familia, por meio de analise de componentes principais. Dados da amostra do Censo Demografico Brasileiro de 2000, realizado pelo Instituto Brasileiro de Geografia e Estatistica, foram usados para gerar o indicador e para o calculo dos pontos de corte dos decis de referencia. RESULTADOS: O indicador, primeiro componente obtido da analise, reteve 38% da variabilidade total e apresentou correlacao de Spearman de 0,74 com a renda total do domicilio e de 0,67 com a renda per capita. Os coeficientes necessarios para calcular o indicador sao apresentados, assim como as distribuicoes de referencia para 27 capitais e Estados, as cinco regioes e o Pais. Apresenta-se um exemplo de como se usa o indicador. CONCLUSOES: Diferentemente de outros indicadores economicos disponiveis, o IEN tem as distribuicoes de referencia publicadas, para capitais, Estados, Regioes, bem como a distribuicao nacional. Torna-se possivel, portanto, comparar a amostra estudada a distribuicao municipal, estadual ou nacional. O numero reduzido de variaveis torna facil o calculo do Indicador Economico Nacional para investigadores envolvidos em pesquisas onde e importante a classificacao economica.

Narrowing socioeconomic inequality in child stunting: the Brazilian experience, 1974-2007

OBJECTIVE To assess trends in the prevalence and social distribution of child stunting in Brazil to evaluate the effect of income and basic service redistribution policies implemented in that country in the recent past. METHODS The prevalence of stunting (height-for-age z score below -2 using the Child Growth Standards of the World Health Organization) among children aged less than 5 years was estimated from data collected during national household surveys carried out in Brazil in 1974-75 (n = 34,409), 1989 (n = 7374), 1996 (n = 4149) and 2006-07 (n = 4414). Absolute and relative socioeconomic inequality in stunting was measured by means of the slope index and the concentration index of inequality, respectively. FINDINGS Over a 33-year period, we documented a steady decline in the national prevalence of stunting from 37.1% to 7.1%. Prevalence dropped from 59.0% to 11.2% in the poorest quintile and from 12.1% to 3.3% among the wealthiest quintile. The decline was particularly steep in the last 10 years of the period (1996 to 2007), when the gaps between poor and wealthy families with children under 5 were also reduced in terms of purchasing power; access to education, health care and water and sanitation services; and reproductive health indicators. CONCLUSION In Brazil, socioeconomic development coupled with equity-oriented public policies have been accompanied by marked improvements in living conditions and a substantial decline in child undernutrition, as well as a reduction of the gap in nutritional status between children in the highest and lowest socioeconomic quintiles. Future studies will show whether these gains will be maintained under the current global economic crisis.

How changes in coverage affect equity in maternal and child health interventions in 35 Countdown to 2015 countries: an analysis of national surveys

BACKGROUND Achievement of global health goals will require assessment of progress not only nationally but also for population subgroups. We aimed to assess how the magnitude of socioeconomic inequalities in health changes in relation to different rates of national progress in coverage of interventions for the health of mothers and children. METHODS We assessed coverage in low-income and middle-income countries for which two Demographic Health Surveys or Multiple Indicator Cluster Surveys were available. We calculated changes in overall coverage of skilled birth attendants, measles vaccination, and a composite coverage index, and examined coverage of a newly introduced intervention, use of insecticide-treated bednets by children. We stratified coverage data according to asset-based wealth quintiles, and calculated relative and absolute indices of inequality. We adjusted correlation analyses for time between surveys and baseline coverage levels. FINDINGS We included 35 countries with surveys done an average of 9·1 years apart. Pro-rich inequalities were very prevalent. We noted increased coverage of skilled birth attendants, measles vaccination, and the composite index in most countries from the first to the second survey, while inequalities were reduced. Rapid changes in overall coverage were associated with improved equity. These findings were not due to a capping effect associated with limited scope for improvement in rich households. For use of insecticide-treated bednets, coverage was high for the richest households, but countries making rapid progress did almost as well in reaching the poorest groups. National increases in coverage were primarily driven by how rapidly coverage increased in the poorest quintiles. INTERPRETATION Equity should be accounted for when planning the scaling up of interventions and assessing national progress. FUNDING Bill & Melinda Gates Foundation; World Bank; Governments of Australia, Brazil, Canada, Norway, Sweden, and UK.

The 2004 Pelotas birth cohort: methods and description

OBJECTIVE To describe a birth cohort which started in 2004, aiming to assess pre and perinatal conditions of the newborns, infant morbimortality, early life characteristics and outcomes, and access, use and financing of health care. METHODS All children born in the urban area of Pelotas and Capão do Leão municipalities (Southern Brazil) in 2004 were identified and their mothers invited to join the study. In the first year of the study the children were seen at birth, at three and 12 months of age. These visits involved the application of a questionnaire to the mothers including questions on health; life style; use of health services; socioeconomic situation; estimation of gestational age; anthropometric measurements on the newborn (weight, length, head, chest and abdominal circumferences); anthropometric measurements on the mother (weight and height) and assessment of infant development. RESULTS Out of the eligible infants (4,558), more than 99% were recruited to the study at birth. Follow-up rates were 96% at three months and 94% at 12 months of age. Among the initial results we highlight the following. Infant mortality rate was 19.7 per thousand, with 66% of infant deaths occurring in the neonatal period. There were frequencies of 15% premature babies and 10% low birthweight. Cesarean sections represented 45% of deliveries. CONCLUSIONS The third Pelotas birth cohort showed an infant mortality rate similar to that of 11 years ago, with most deaths occurring in the neonatal period. The rates of prematurity and cesarean sections increased substantially.