¹Hamad Medical Corporation, CCS Department, Medical Research Centre- Cardiology, Doha, Qatar. Senior consultant. Email: rajvir.aiims@gmail.com
²The University of the West Indies, Faculty of Science and Agriculture, Department of Mathematics & Statistics, Trinidad & Tobago, West Indies. Lecturer. Email: Vrijesh.Tripathi@sta.uwi.edu
³All India Institute of Medical Sciences, Department of Biostatistics, New Delhi, India. Scientist. Email: manikalaivani@gmail.com
⁴Max Healthcare Institute Ltd., Clinical Research Department, New Delhi, India. Researcher. Email: nkalpanasingh@gmail.com
⁵All India Institute of Medical Sciences, Department of Biostatistics, New Delhi, India. Professor. Email: dwivedi7@hotmail.com

The present study uses data from National Family Health Survey (NFHS-1) 1992-93 (International Institute for Population Sciences 1995) conducted in the state of Tamil Nadu, India. Cox models were developed to analyze the effect of breastfeeding as time varying and time dependent factor on birth intervals. Breastfeeding alone improved the log likelihood up to a higher level in each birth interval. Other factors that entered into the models were: at first birth interval, womens education (high school & above) and working status of women; at second birth interval, survival status of index child alive and husbands education (high school & above), and at third birth interval, breastfeeding more than 22 month were found to be protective factors for next births. Validation of the developed models was done through bootstrapping to predict birth intervals.

Key words: Cox model, Multivariate analysis, Validation, Predictions.

Este estudio utiliza datos de la Encuesta Nacional de Salud Familiar (International Institute for Population Sciences 1995) realizada en el estado de Tamil Nadu, India. Se desarrollaron modelos de Cox para analizar el efecto de la lactancia materna cuando varía en el tiempo y el factor tiempo depende de los intervalos genésicos. La lactancia materna sólo mejora la probabilidad de acceder a un nivel más alto en cada intervalo de nacimiento. Otros factores que entraron en los modelos fueron en el intervalo del primer parto: nivel educativo de la madre (secundaria y superior) y trabajo de la madre; en el intervalo del segundo parto: nivel de supervivencia en el índice de vida infantil y nivel educativo del padre (secundaria y superior), y en el intervalo del tercer parto: lactancia materna más 22 meses. Cada uno de los anteriores es un factor protector para ampliar el intervalo entre nacimientos en el estudio. Además, este estudio confirma los modelos desarrollados en los servicios públicos de predicción para los intervalos genésicos.

Palabras clave: análisis multivariado, modelo de Cox, predicciones, validación.

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