Resumen
Dos problemas van asociados con el uso efectivo de anticonceptivos. Primero, parejas que pertenecen a una muestra de practicantes, varían típicamente de acuerdo con la probabilidad mensual de fracaco del método. Segundo, no es posible observar a muchas y posiblemente a la mayoría de ellas el tiempo que pueden estar protegridas por el anticonceptivo, porque o suspenden su uso para un embarozo planeado, o se interrumpe la observación por pérdida de contacto con la pareja; puede haber también suspensión del uso por otras razones o se puede descontinuar el estudio de observación. Por estos problemas—Uamémoslos heterogeneidad de la muestra e historias incompletas—se sostiene que la tasa de embarazos de Pearl, que ha sido tradicionalmente usada para medir la anticoncepción es inadecuada.
Un método similar al de construcción de tablas de vida se describe aquí, el cual permite la combinación de historias completas e incompletas con el propósito de estimar proporciones en las mujeres de la muestra que pudieron haber permanecido protegridas durante periódos específicos si todos los miembros de la muestra hubieran permanecido bajo observación en dichos períodos. La versatilidad del sistema es ilustrada con una encuesta retrospectiva, en donde se describe el procedimiento detalladamente. Finalmente, se muestra que sólo en condiciones específicas que raramente se encuentran en la práctica, es posible estimar los resultados de nuevas técnicas con el solo conocimiento de las tasas dePearl.
Summary
Two problems are associated with the analysis of use-effectiveness of contraception. First, couples belonging to a sample of contraceptors typically vary in their monthly chances of contraceptive failure. Second, one does not observe for many, and perhaps a majority of the couples, how long they can remain protected with the contraceptive, because either they are stopping contraception to plan a pregnancy or else observation of them is being interrrupted by lost contact, by discontinuation of contraception for other reasons, or by the end of the study. It is argued that because of these two problems—namely, sample heterogeneity and incomplete histories-the Pearl pregnancy rate, which has been traditionally used to measure contraceptive effectiveness, is inadequate.
A life table method is described that permits one to combine incomplete histories with complete ones for purposes of estimating the proportions of the sample that might have remained protected for specified periods if all members had remained under observation for these periods. The versatility of the techniques is illustrated in relation toa retrospective survey. A detailed account of procedure is given. Finally, it is shown that only under specialized conditions that are rarely met in practice is it possible to estimate the results of the new technique from knowledge of Pearl pregnancy rates alone.
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References
Cf. M. C. Sheps, “On the Person Years Concept in Epidemiology and Demography,” Milbank Memorial Fund Quarterly, XLIV, No. 1, Part 1 (January, 1966), 69–91; L. Lasagna, “The Quantification of Desired and Undesired Effects of Reproductive Controls: Some Principles and Problems,” in M. C. Sheps and J. C. Ridley (eds.), Public Health and Population Change: Current Research Issues (1966, in press); R. G. Potter, “Contraceptive Practice and Birth Intervals among Two-Child White Couples in Metropolitan America,” in Thirty Years of Research in Fertility: Retrospect and Prospect (New York: Milbank Memorial Fund, 1958), pp. 74–92; M. Seklani, “Efficacité de la Contraception: Méthodes et Réaultats,” Population, XVIII, No.2 (1963), 329–46; C. Tietze, “The Use-Effectiveness of Contraceptive Methods,” in C. V. Kiser (ed.), Research in Family Planning (Princeton: Princeton University Press (1962), pp. 357–69; and “Differential Fecundity and Effectiveness of Contraception,” Eugenics Review, L (January, 1959), 231–37.
R. G. Potter, “Additional Measures of Use-Effectiveness of Contraception,” Milbank Memorial Fund Quarterly, XLI (October, 1963), 400–418. See also C. Tietze and S. Lewit, “Recommended Procedures for the Study of Use-Effectiveness of Contraceptive Methods,” I.P.P.F. Medical Handbook (London; Part I [n.d.], pp. 59–69; Part I, 2d ed. [1964], pp. 58–61).
R. G. Potter, “Length of the Observation Period as a Factor Affecting the Contraceptive Failure Rate,” Milbank Memorial Fund Quarterly, XXXVIII (April, 1960), 140–52.
Tietze and Lewit, op. cit. C. Tietze and S. Lewit, “Recommended Procedures for the Study of Use-Effectiveness of Contraceptive Methods,” I.P.P.F. Medical Handbook (London; Part I [n.d.], pp. 63–64.
A more extensive discussion of this estimator is given in Potter, “Additional Measures of Use-Effectiveness of Contraception,” Milbank Memorial Fund Quarterly, XLI (October, 1963), 400–418.
C. Tietze, “History and Statistical Evaluation of Intra-uterine Contraceptive Devices,” in Sheps and Ridley (eds.) Public Health and Population Change …, and C. Tietze and S. Lewit, “Intra-uterine Contraception: Effectiveness and Acceptability,” in S. J. Segal et al., Intra-uterine Contraception (New York: Excerpta Medica Foundation, 1965), pp. 98–110.
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This research was conducted under grant funds from the Ford Foundation. This is a revised version of a paper presented at the United Nations World Population Conference, Belgrade, Yugoslavia, September, 1965.
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Potter, R.G. Application of life table techniques to measurement of contraceptive effectiveness. Demography 3, 297–304 (1966). https://doi.org/10.2307/2060159
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DOI: https://doi.org/10.2307/2060159