For the Record
On the “doctoring” of population statistics
This article seeks to clarify some of the points and misconceptions mentioned in the article entitled “Population Statistics are Being Doctored,” which appeared in the “Business and Society” column of Dr. Bernardo Villegas in the 20 September 2010 issue of the Manila Bulletin (http://www.mb.com.ph/articles/277855/population-statistics-are-being-doctored).
Statement: “…in projecting population data from the 2000 census, some of the statisticians in the NSCB single-handedly added 146,582 babies to the actual number recorded in the 2000 census.”
The NSCB already responded to the issue originally raised by Dr. Jose S. Sandejas in a letter addressed to the Secretary of Socioeconomic Planning and Chairman of the NSCB Executive Board, Cayetano W. Paderanga, Jr., dated 2 September 2010 with clarification on the generation of population projections as well as the methodology involved in the process.
Relatedly, Secretary Paderanga also responded to the issue, in his letter dated 13 September 2010 to Dr. Sandejas.
The statements below were largely culled from the documentation of the population projection methodology attached as a technical annex to NSCB Board Resolution No. 7, Series 2006 entitled
“A Brief Description of the Methodology for the 2000 Census-Based Population Projections”
(http://www.nscb.gov.ph/resolutions/2006/7Annex.pdf) prepared by the NSCB-created interagency Technical Committee on Population and Housing Statistics (TCPHS), with additional supporting information.
1. On the interagency collaboration in the preparation of population projections
The generation of population projections is a collaborative effort among various agencies, including the academe. Per Executive Order No. 352 on the System of Designated Statistics, the TCPHS is in charge of coming up with the projection methodology, while the National Statistics Office (NSO) is designated to undertake the actual computation of the population projections.For the 2000 round of projections, the NSO created the Interagency Working Group (IAWG) on Population Projections, composed mainly of experts in the field of demography and chaired by NSO Administrator Carmelita Ericta. The IAWG, in turn, created four small working groups (SWGs), consisting of statisticians and demographers, to discuss in detail the assumptions to be used for the population projections concerning the base population, fertility, mortality, and migration. The SWGs were chaired by proficient demographers with particular expertise in these four areas of concern, i.e., Dr. Socorro Abejo of NSO (base population), Dr. Zelda Zablan of the Demographic Research and Development Foundation (fertility), Dr. Josefina Cabigon of the University of the Philippines Population Institute or UPPI (mortality), and Dr. Nimfa Ogena, also of UPPI (migration).
2. On the methodology
The methodology for the population projections, including the assumptions, went through a rigorous review process based on empirical evidence and informed by recent survey findings and administrative records. This was undertaken by the TCPHS, chaired by 2010 National Scientist Dr. Mercedes B. Concepcion, which endorsed it for approval of the NSCB Executive Board. Based on the recommendation of the TCPHS, the Board approved the methodology in February 2006 and endorsed the resulting population projections as the official figures to be utilized for planning and programming purposes.
3. On the base population
The base population used in these projections was the population enumerated during the 2000 Census of Population and Housing (CPH). The final population count as of 1 May 2000 was 76,504,077, which was forward-survived to 1 July 2000 after evaluating the age-sex distribution using indexes in assessing the quality of age-sex data (i.e., the UN Age-Sex Accuracy Index, Myer’s Index, and Whipple and Bachi indexes).
Although the indexes indicated minimal age heaping and digit preference, the proportion of the population aged 0-4 years was smaller than the proportion of the population aged 5-9 years in 58 out of 79 provinces. This clearly should not have been the case since it was inconsistent with the still relatively high and slowly declining fertility observed at the national and regional levels based on the quinquennial National Demographic Surveys (later expanded and renamed as the National Demographic and Health Survey or NDHS) conducted from 1968 to 2003. This fertility trend indicated a relatively young population, or specifically, a larger population aged 0-4 compared to the population aged 5-9. A close examination of the census survival ratios for these age groups and fertility and migration rates revealed a likely larger population aged 0-4 than what was reported in the census for the same age group. The smaller size of the population aged 0-4 compared to the population aged 5-9 for the 58 provinces in question implied an underenumeration of the population aged 0-4 years. As observed in most countries, the population below age 1 is the most underenumerated.
To adjust the population below 1 year of age, the number of births at the national level for year 2000 was estimated based on estimates of total fertility rates (TFRs) and age specific fertility rates (ASFRs) from the 1998 and 2003 NDHS. In order to obtain an estimate of the population below 1 year of age (Po) in 2000, these births were forward-survived to age below 1 year by applying the 1995 life table values of the proportion of infants born in a year who will survive to the end of that year calculated by Flieger and Cabigon (1999).
4. On the adjustment of the base population, not the population count
The difference between the estimated base population (Po) and the enumerated Po in year 2000 totaled 146,582. This number was added to the July 1, 2000 population aged 0 after extrapolating the enumerated May 1, 2000 population using the average annual population growth rate between May 1, 1990 and May 1, 2000.
It must be emphasized that the IAWG did not adjust the base population with the intent of changing the actual census count of children aged 0-4, but only for the purpose of coming up with the 2000-based population projections. As discussed above, this was deemed necessary based on an evaluation of the census survival ratios for age group 0-4 vis-à-vis fertility and migration rates undertaken by the SWG on Base Population, which revealed a likely larger population aged 0-4 than what was reported in the census for the same age group.
It must also be noted that the use of adjustment factors for the base population for projections is an internationally accepted practice among demographers, including those of the United Nations Population Division, to address the common problem of under enumeration in the population census, particularly for the youngest age group. Note that the 1990 and 1995 population projections also had some adjustments in the base population.
Statement: “…the Philippines' National Statistical Coordination Board in its website, quotes the Philippine Population Growth Rate (PPGR) for the year 2010 to be at the low level of only 1.82% per annum (vs. the 2.36% during the census year 2000, which figure is often still used to justify the view that PGR is ‘exploding.’ ”
It must be stressed that the population growth rates reflected in the NSCB web page on population projections (http://www.nscb.gov.ph/secstat/d_popnProj.asp) refer to the projected average annual rates of increase of the Philippine population for specific periods computed using exponential growth. Thus, the population growth rate of 1.82 percent represents the projected average annual rate of increase for the period 2010-2015. This figure and the other projected values from the table should be interpreted with caution, as these are projections based on certain assumptions of fertility and mortality, and hence, should not be taken as growth figures that have already been attained.
On the other hand, the growth figure of 2.36% mentioned in the article is the average annual population growth rate for 1995-2000 based on the actual 1995 and 2000 population census results.
Statement: “Equally worrisome is the Total Fertility Rate (TFR), the average number of children per woman, quoted by NSCB for the year 2010 at only 2.96 births per woman. This represents a big decline from the 2000 figure of 3.41 births per woman.”
Total fertility rate (TFR) refers to the average number of children that a woman of reproductive age would have in her lifetime. The TFR figures of 2.96 and 3.41 both represent the projected (not actual) average number of children that would be born alive for the period 2010-2015 and 2000-2005, respectively, to a woman (or group of women) during her lifetime, if she were to pass through her childbearing years (15-49) conforming to the age specific fertility rates of a given period.
We would like to stress that the official figures for population projections and other statistics released by the Philippine Statistical System are guided by basic principles of truth and professional integrity. The NSCB is committed to promote and maintain an efficient government statistical system that provides adequate, accessible, consistent, reliable, and timely data. We produce and compile information founded on scientific research, wide consultation, and professional discussion. To retain the trust in official statistics produced and disseminated by the PSS, we abide by the United Nations’ Fundamental Principles of Official Statistics.
And finally, we would like to assure Dr. Villegas that we, in the NSCB, are professional statisticians and we “do not engage in abracadabra”!
The NSCB would like to thank Dr. Bernardo Villegas of the Manila Bulletin for his interest in our statistics.
For further inquiries, please contact Ms. Didi M. Ignacio of the NSCB Social Sectors A Division at telephone numbered (632)890-9678 or through e-mail address rm.ignacio @nscb.gov.ph
The complete composition of the TCPHS in 2006 was as follows:
Chairperson: Dr. Mercedes B. Concepcion
National Academy of Science and Technology
Vice-Chairpersons: Ms. Nelia R. Marquez
Dr. Grace T. Cruz
University of the Philippines Population Institute
Members: Ms. Paula Monina G. Collado
National Statistics Office
Dr. Socorro N. Abejo
National Statistics Office
Dr. Josefina V. Cabigon
Dr. Zelda C. Zablan
Ms. Myrna B. Asuncion
National Economic and Development Authority
Ms. Mia C. Ventura
Commission on Population
Ms. Ma. Criselda R. Sy
Bureau of Labor and Employment Statistics
Department of Labor and Employment
Mr. Ronald G. Fontamillas
Housing and Urban Development Coordinating Council
Ms. Belen Cenizal
Housing and Land Use Regulatory Board
Dr. Jose Ramon G. Albert
Statistical Research and Training Center
Ms. Marilou Alferez
Subdivision and Housing Developers’ Association
Ms. Lina V. Castro
National Statistical Coordination Board
Ms. Fe Vida N. Dy-Liacco
National Statistical Coordination Board
Posted: 22 September 2010.