Resumen

El méetoda corriente de elaboración de proyecciones de la fecundidad, que puede denominarse “métoda del período de fecundidad,” no permite distinguir una tendencia de fluctuación. En cambio, el “método de la fecundidad de la cohorte” al identificar la fecundidad total de una cohorte con la tendencia y al explicar las fiuctuaciones en la fecundidad del período en función de cambios de la edad media de las madres, permite distinguirla. Los cambios en la edad de la madre conducen a una concentración 0 extensión de los nacimientos con las correspondientes desviaciones de la iendencia. Tal es el fenómeno que Whelpton denominó “pedir prestado del futuro,” pero que en términos más gráficos podría denomi narse “efecto de acordón.”

El métoda de la fecundidad de la cohorte es deficiente:(a) porque no constituye un método efectivo para analizar la edad de las madres, y(b) porque no permite distinguir siquiera una transición en la fecundidad entre el primer año proyectado y el precedente. La experiencia pasada muestra que no cabe esperar fluctuaciones agudas en el término de un oño.

El métoda de la progresión de la paridez supera eetas deficiencias por cuanto él representa efectivamente la distribución de las mujeres en el ciclo de formación de la familia. El factor determinante más importante de la fecundidad a corto plazo es esta distribución mas que las expectativas a largo plazo acerca del tamaño de la familia 0 del estado de la economia. Un factor esencial del método es el intervalo. Las proyecciones experimentales que usan la paridez pero que omiten el intervalo, dan resultados deficientes.

Una especie de síntesis del método de progresión de la paridez y del métoda de la fecundidad por cohortes podría proporcionar distribuciones razonables de los nacimientos por edad de la madre, y de la mujeres según la paridez al término del período de fecundidad, y permitiría elaborar proyecciones aceptables a corto y a largo plazo.

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References

1
For discussion of recent trends, see the following: Pascal K. Whelpton, “Why Did the United States Crude Birth Rate Decline during 1957–1962?”Population Index (April, 1963); Anders Lunde, Carl Ortmeyer, and Earl Huyck, “Marriages, Births, and Population Growth,” Health, Education, and WelfareIndicators (March, 1953); Morris Axelrod, Ronald Freedman, David Goldberg, and Doris Slesinger, “Fertility Expectations of the United States Population—a Time Series,”Population Index (January, 1963); Donald Freedman, David Goldberg, and Doris Slesinger, “Current Fertility Expectations of Married Couples in the United States,”Population Index (October, 1963). See also the chapter by Arthur A. Campbell in a forthcoming report of the Subcommittee on Fertility Measurement of the U.S. National Committee on Vital and Health Statistics.
2
See Bureau of the Census,Current Population Reports, Series P-25, No. 286, “Projections of the Population of the United States by Age and Sex: 1964 to 1985, with Extensions to 2010,” by Jacob S. Siegel, Meyer Zitter, and Donald S. Akers (July, 1964). The projections first appeared in an advance report-s-Series P-25, No. 279 (February, 1964). The previous projections appeared in Series P-25, No. 187, “Illustrative Projections of the Population of the United States, by Age and Sex: 1960 to 1980,” by Meyer Zitter and Jacob S. Siegel (November, 1958). The series was carried forward to the year 2000 in U.S. Senate Select Committee on National Water Resources,Water Resources Activities in the United States (Population Projections and Economic Assumptions, Committee Print No.5, 1960), p. 26. An interim revised series appeared in Series P-25, No. 241, “Interim Revised Projections of the Population of the United States, by Age and Sex: 1965 and 1970” (June 1962), and No. 251, “Interim Revised Projections of the Population of the United States, by Age and Sex: 1975 and 1980” (July 1962).
3
For examples of the period fertility method, see the following: Series P-25, No. 187; Bureau of the Census, “Forecasts of the Population of the United States: 1945–1975,” by P. K. Whelpton, Hope Tisdale Eldridge, and Jacob S. Siegel (Government Printing Office, 1947).
4
For descriptions of the cohort method, see the following: P-25, No. 286, pp. 12–23; Pascal K. Whelpton,Cohort Fertility, Native White Women in the United States, Princeton University Press, 1954; Pascal K. Whelpton and Arthur A. Campbell, “Fertility Tables for Birth Cohorts of American Women,” Part I, in Public Health Service, National Office of Vital Statistics,Vital Statistics—Special Reports, Selected Studies, Vol. 51, No. 1 (June 1960); Ronald Freedman, Pascal K. Whelpton, and Arthur A. Campbell,Family Planning, Sterility, and Population Growth, (McGraw-Hill, 1959), chap. x, “Future Trends in Family Size”; Pascal K. Whelpton, “Cohort Analysis and Fertility Projections,”Emerging Techniques in Population Research, Milbank Memorial Fund, 1963. A book by Pascal K. Whelpton, Arthur A. Campbell, and John E. Patterson is in preparation which analyzes the results of the “Growth of American Families” survey of 1960.
5
For discussions of the parity progression method, see the following: P-25, No. 286, pp. 35–37; Guy H. Orcutt, Martin Greenberg, John Korbell, and Alice M. Rivlin,Micro-analysis of Socioeconomic Systems: A Simulation Study, Part II, “A Demographic Model of the U.S. Household Sector,” Harper & Bros., 1961; Alice M. Rivlin, “The Use of Computer Simulation in Population Studies: An Illustration,” International Population Conference, New York, 1961; Wilson H. Grabill, “Derivation of Age-Specific First Marriage Rates and of Birth Rates Specific for Order of Birth and Interval since First Marriage or since Birthdate of the First Child,” unpublished white paper; and internal memoranda of the Bureau of the Census by Howard G. Brunsman and by James Beshers.
6
Norman B. Ryder, “Problems of Trend Determination during a Transition in Fertility,”Milbank Memorial Fund Quarterly (January, 1956).
7
Norman B. Ryder, “The Structure and Tempo of Current Fertility,” in National Bureau of Economic Research,Demographic and Economic Change in Developed Countries, Princeton University Press, 1960; “The Translation Model of Economic Change,”Emerging Techniques in Population Research, Milbank Memorial Fund, 1963; “The Process of Demographic Translation,”Demography, Vol. I, No.1, 1964.
12
For a discussion of the stability of the birth rate, see Dudley Kirk, “The Influence of Business Cycles on Marriage and Birth Rate,” in National Bureau of Economic Research,Demographic and Economic Change in Developed Countries, Princeton University Press, 1960.
13
Grabill,op. cit. Wilson H. Grabill, “Derivation of Age-Specific First Marriage Rates and of Birth Rates Specific for Order of Birth and Interval since First Marriage or since Birthdate of the First Child,” unpublished white paper.
14
Joseph Schachter, Deward E. Waggoner, and Pascal K. Whelpton, “Short Range Birth Projections,”Public Health Reports, (November, 1958).
16
Orcutt,Micro-analysis of Socio-economicSystems; Howard G. Brunsman, “Significance of Electronic Computers for Users of Census Data,”Emerging Techniques of Demographic Research, Milbank Memorial Fund, 1963; James M. Beshers, “Cohort Projection Models,” paper presented at the annual meeting of the Population Association of America, San Francisco (June 11, 1964).
17
U.S. Bureau of Labor Statistics, Bull. No. 1242, “Population and Labor Force Projections for the United States, 1960 to 1975,” by Sophia Cooper and Stuart Garfinkle (1959), pp. 33–37.
18
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19
For a step in this direction, see Nathan Keyfitz, “The Population Projection as a Matrix Operator,”Demography, Vol. I, No. 1, 1964.

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