It is designed to provide information on:
- the determining factors on the decision to have children or not, such as: educational level, income, reconciliation, availability of support, life as a couple, delay in emancipation, etc.
- the reasons leading to the delay in parenthood
- and on the changes in family structures and on the couple/child relations and their influence on the fertility of the populations, which will help in the preparation of population forecasts and projections. For the first time, men are also investigated in order to understand their familial and reproductive behaviour and thus have a gender perspective given that their work and family trajectories and their reproductive aspirations also have a direct impact on fertility.
The FS2018 provides data at the national level, for both men and women, and data broken down by Autonomous Community for women only, according to basic demographic characteristics, such as sex, age, nationality, income level, marital status, emotional situation, the level of education achieved, the employment situation, the number of children they have, the number of children they want and those they intend to have, barriers and incentives to the birth rate and types of assisted reproduction they have used, if applicable, according to the INE standardised classifications.
Specifically, the FS2018 uses three standardised classifications in its use of results:
-National Classification of Occupations NCO 2011: The occupation is coded at a two-digit level.
- National Classification of Education CNED14-P: The level of studies achieved is classified according to the aggregation of the CNED codes. The CNED-P is the reference classification to collect information on ongoing studies, and therefore its scope covers current programmes relating to both formal and non-formal education.
- National Classification of Economic Activities NCAE 2009: The activity is coded at a one-digit level.
The research is aimed at the group of persons aged 18 to 55, both ages included, who reside in the main family dwellings throughout the national territory.
The institutionalised population is not considered.
People from 18 to 55 years old, both ages included, residing in main family dwellings.
The population scope of the survey is made up of people between the ages of 18 and 55, both ages included, who live in family households. Persons of said ages residing in institutions or collective establishments are excluded.
The survey is aimed at an individual person, not at the dwelling, and an indirect respondent other than the selected person is not allowed to respond.
National and Autonomous Community results are provided for women and national results are provided for men.
The first Fertility Survey conducted by the INE was carried out in 1977. Since then, 4 editions have been carried out with non-regular periodicity.
The target population of the survey has been different in each edition.
The FS1977 was aimed at women aged 15 to 49 who had been married before.
The FS1985 was aimed at all women aged 18 to 49 regardless of their marital status.
The FS1999 addressed all women aged 15 to 49 regardless of their marital status.
The FS2018 targeted men and women aged 18 to 55, both ages included, living in main family dwellings.
Number of persons (Data provided in terms of absolute figures)
Percentage of persons (Data provided in terms of relative figures)
The time period to which the data refers varies according to the nature of the variables to be investigated. In general, the reference period, i. e., the period to which the situation of the person interviewed refers, is the date on which the interview is conducted.
Data referred to the period: EF2018 Definitivos
The compilation and dissemination of the data are governed by the Statistical Law No. 12/1989 "Public Statistical Function" of May 9, 1989, and Law No. 4/1990 of June 29 on “National Budget of State for the year 1990" amended by Law No. 13/1996 "Fiscal, administrative and social measures" of December 30, 1996, makes compulsory all statistics included in the National Statistics Plan. The National Statistical Plan 2009-2012 was approved by the Royal Decree 1663/2008. It contains the statistics that must be developed in the four year period by the State General Administration's services or any other entity dependent on it. All statistics included in the National Statistics Plan are statistics for state purposes and are obligatory. The National Statistics Plan 2017-2020, approved by Royal Decree 410/2016, of 31 October, is the Plan currently implemented. This statistical operation has governmental purposes, and it is included in the National Statistics Plan 2017-2020. (Statistics of the State Administration).
The INE adopts the logical, physical and administrative measures necessary for the effective protection of confidential data, from the collection of data to its publication.
The survey questionnaires include a legal clause that states the protection covering the data collected.
During the information processing phases, data allowing direct identification is only kept for as long as it is strictly necessary to guarantee the quality of the processes.
In the publication of the results tables, the detail of the information is analysed to prevent confidential data of the statistical units being deduced.
Microdata files are always anonymous.
The Fertility Survey is a statistical operation that the INE has carried out on four occasions without a fixed periodicity.
All information on the survey can be found at:
INEbase is the system the INE uses to store statistical information on the Internet. It contains all the information the INE produces in electronic formats. The primary organisation of the information follows the theme-based classification of the Inventory of Statistical Operations of the State General Administration . The basic unit of INEbase is the statistical operation, defined as the set of activities that lead to obtaining statistical results on a determined sector or subject based on the individually collected data. Also included in the scope of this definition are synthesis preparation.
Access to tables and time series in INEbase within the section "Demography and population" at www.ine.es:
In 2017, the number of consultations to the results tables was AC1= 22,340.
The anonymised microdata file of FS2018 is available on the INE website.
In order to guarantee confidentiality, certain variables (name and surname, province of residence,...) will be removed. Users may request some unpublished variable in accordance with the strict confidentiality requirements. Requests should be addressed to the INE. A description of how to make a tailored request can be found here:
This operation allows users' requests for tailored information not considered in the results tables to be met, after a feasibility study, in any case, by the INE.
A detailed description of the FS2018 methodology is available on the INE website.
Fields 10.6 to 17 of this document are the user-oriented quality report for this operation.
Quality assurance framework for the INE statistics is based on the ESSCoP, the European Statistics Code of Practice made by EUROSTAT. The ESSCoP is made up of 16 principles, gathered in three areas: Institutional Environment, Processes and Products. Each principle is associated with some indicators which make possible to measure it. In order to evaluate quality, EUROSTAT provides different tools: the indicators mentioned above, Self-assessment based on the DESAP model, peer review, user satisfaction surveys and other proceedings for evaluation.
For FS2018, a series of measures have been implemented to help ensure the quality of the process and results. Among them are the following:
-Creation of a working group with the participation of experts in demography from the Consejo Superior de Investigaciones Cientificas (Spanish National Research Council or CSIC), the Centro de Estudios Demograficos de la Universidad de Barcelona (Centre for Demographic Studies at the University of Barcelona or CED) and the INE for the creation of the questionnaire.
- The information collection method of this survey has been multichannel sequential. The main one being the web-based interview (CAWI), complemented by a telephone interview (CATI) and a personal interview (CAPI). In the three cases, the data collection has been carried out through an electronic questionnaire supported by a computer application, which incorporates checks on range, flow, completeness and validity that are in operation during the collection itself with the aim of carrying out an initial filtering in the field in the same household where the information is collected.
-Specific interviewer training
-Periodic inspection of the field work
-Exhaustive revision of the question codings that require it (level of education achieved, activity and occupation)
-Control of errors and post-collection warnings in order to corroborate the correct functioning of the applications and avoid systemic errors in the collection.
According to the measures implemented in the collection process and filtering of results described in the previous section, the strengths of the survey are:
-the completeness of the questionnaire as it contains the different aspects that may appear in a fertility survey.
- the absence of errors and inconsistencies between the responses to the questionnaire thanks to the electronic questionnaire (CAWI, CATI, CAPI) and an initial filtering in the field.
-adequate classification according to sociodemographic variables due to the exhaustive filtering of the variables on activity, occupation, level of education achieved and household composition.
-results measured by age, sex, nationality and provincial totals and in the case of women, also by Autonomous Community totals.
As for the survey limitations, it is important to point out those that are inherent to sampling statistical operations, such as non-response and sampling errors or coefficients of estimation variation. In both cases, they are kept within reasonable limits.
The main users of the survey results are researchers and universities, specialised press and media and, in general, anyone interested in analysing the low levels of fertility that Spain experiences, which does not ensure generational replacement and which will have direct consequences on the future of our labour market, our social protection systems, etc.
The INE has carried out general user satisfaction surveys in 2007, 2010, 2013 and 2016 and it plans to continue doing so every three years. The purpose of these surveys is to find out what users think about the quality of the information of the INE statistics and the extent to which their needs of information are covered. In addition, additional surveys are carried out in order to acknowledge better other fields such as dissemination of the information, quality of some publications...
On the INE website, in its section Methods and Projects / Quality and Code of Practice / INE quality management / User surveys are available surveys conducted to date.(Click next link)
The Fertility Surveys carried out by the INE are widely used by demographics researchers, part of whose research is published in various prestigious national and international journals.
There is no specific user satisfaction survey for FS2018; however, the user satisfaction surveys by INE indicate the user group's level of satisfaction with the Demography and Population statistics.
The 2018 Fertility Survey is included in the 2017-2020 National Statistics Plan, with code 7869 and its code in the Inventory of Statistical Operations (this code is a fixed identifier for the statistical operation, which does not change) is 30317.
This operation complies 100% (R1=100) with the purposes stipulated by the 2017-2020 National Statistics Plan, providing information on the fertility of the Spanish population and its socio-demographic characteristics, as can be seen in the 2018 Annual Programme for the development of said Plan (https://www.ine.es/normativa/leyes/plan/plan_2017-2020/calendario2018_en.pdf).
The survey is not regulated by any European directive. The requirements are dictated by the needs of expert researchers in the field of demography. To this end, a working group was set up with experts in demography from the CSIC, CED and the INE, whose objective was to incorporate all those considerations which, in the opinion of the group, could influence a priori people's fertility decisions, but also to ensure that the 2018 fertility survey had certain comparability with previous surveys carried out in Spain as well as with similar surveys carried out in other countries.
In this process, a dozen or so questionnaires used in recent research in other countries were extensively analysed and it was decided that the questionnaire should largely follow the United Nations project "Generations and Gender Survey", which has been used by many countries.
All the variables established in the questionnaire could be collected and used. The variable with the greatest partial non-response was that related to income.
The sample design is aimed at minimising sampling errors and the different processes that make up the survey are aimed at reducing non-sampling errors, both in the collection phase and in the subsequent filtering and imputing phases.
Calibration techniques have also been applied to reduce bias due to non-response.
Information on sampling errors is available on the INE website, so users can assess the quality of the data presented.
Finally, the exhaustive and centralised filtering of the coding for the level of studies, activity, occupation and household members variables has allowed us to provide a homogeneous and controlled processing of the subsequent classifications of the sample, also avoiding biases in the results of certain areas or groups.
These sampling errors can be found within the tabulation of the survey.
In the survey methodology, which is available on the INE website, non-sampling errors are reported.
The main source of non-sampling errors is due to the non-response of the persons selected for the sample. Fertility surveys, both in terms of the type and the volume of information collected in them, have traditionally been unpopular with the public, meaning that collaboration rates tend to be among the lowest within household surveys.
Non-response rate on the total number of surveys: A4= 30.1%
The total number of both manual and automatic account assignments was less than 1% of the total number of data (A7 = <1%).
The over-coverage rate or proportion of units outside the scope of the survey was 0.5% (A2 = 0.5%)
The time interval between the end of the reference period (25/6/2018) and the publication date of the preview results is 156 days (TP1=156).
The time interval between the end of the reference period (25/6/2018) and the publication date of the final results is 289 days (TP2=289).
The dissemination of both the preview and the final results of the survey were published according to date foreseen in the structural statistics calendar that the INE prepares and publishes for each year (TP3=0).
The design and the sample size for women allows the comparison of results at Autonomous Community level.
The definitions and concepts used in the survey questionnaire allow the results of the FS2018 to be compared with those of similar surveys in other countries.
The INE has carried out four Fertility Surveys since 1977 without a regular periodicity. However, data from this survey was only published in 1999 and 2018 but the target population addressed by these surveys has been different, therefore temporal comparability remains partially limited.
The main contribution of the survey is the possibility of knowing the current reasons for the phenomenon of Spanish fertility and cross-referencing these variables with sociodemographic variables.
The coherence between the variables is compared when the respondent's data is collected via the computer application (checking for errors and warnings) that contains the electronic questionnaire and is reviewed in the subsequent filtering process. This process has allowed all the variables collected in the questionnaire to be provided.
Additionally, the estimates have complete internal coherence, as they are based on the same data set and are calculated using the same estimation methods at all levels.
The use of an electronic questionnaire reduces the burden on the respondent in terms of interview time or duration, as opposed to the use of a paper questionnaire. Fundamentally, due to the fact that the electronic questionnaire incorporates flow controls in such a way that it automatically directs the respondent through the questions that must be answered in a faster way than when a paper questionnaire is provided.
At the same time, the working group that was created to design the questionnaire made a great effort to reduce the size of the questionnaire, thoroughly analysing the questions from previous editions and the needs of users, removing questions that were not subsequently used or that could be obtained by other sources or giving them a more general approach in this edition in order to introduce other new questions.
The estimate of the budgetary credit necessary to finance this survey foreseen for the four-year period is 1,136.44 thousand euros.
The INE of Spain has a policy which regulates the basic aspects of statistical data revision, seeking to ensure process transparency and product quality. This policy is laid out in the document approved by the INE board of directors on 13 March of 2015, which is available on the INE website, in the section "Methods and projects/Quality and Code of Practice/INE’s Quality management/INE’s Revision policy" (link).
This general policy sets the criteria that the different type of revisions should follow: routine revision- it is the case of statistics whose production process includes regular revisions-; more extensive revision- when methodological or basic reference source changes take place-; and exceptional revision- for instance, when an error appears in a published statistic-.
The definitive survey data is not reviewed and replaces the preview data once disseminated.
The definitive data have been published on April 9, 2019.
No revisions are made.
The preview data published in November 2018 have been subjected to furter filtering and have been used together with the information from some other questionnaires, which at the time of de advance were not yet sufficiently filtered at the time of the preview for the calculation of the definitive data.
The data obtained for this statistical operation is based on a personal survey carried out through an electronic questionnaire.
The questionnaire has been designed to collect information on people aged 18 to 55, both ages included, about their socio-demographic characteristics, those of their partners, ascendants and descendants, their retrospective marital, reproductive and work profiles, as well as their educational history and their values, beliefs and attitudes.
The questionnaire has been structured in ten blocks of questions: biographical data, household, dwelling, parents, relationships, children, fertility, studies, occupation and income and values, beliefs and attitudes. Nine of these ten blocks of questions are common to men and women, and only the one related to fertility is different depending on the sex of the respondent.
In terms of sample design, two independent samples have been selected, one of men and another of women. In both cases, selecting independent samples in each Autonomous Community.
A stratified two-stage sampling has been carried out, using the Continuous Population Register as a framework, in which the first phase units are the census tracts and the second phase units are the persons between 18 and 55 years of age, both ages included, resident in the census tracts that have been selected in the first stage.
Regarding the stratification criterion, the census tracts are stratified within each Autonomous Community according to the size of the municipality to which they belong.
Subsequently a sub-stratification has been carried out within each stratum using the socio-economic information available from the last census.
At the national level, a theoretical sample of 1,886 census tracts has been selected for women and 517 for men, representing a total theoretical sample of 31,570 people that was considered sufficient to obtain an effective sample providing reliable estimates at the Autonomous Community level for women and at the national level for men.
The 517 sections for which the male sample has been collected is a sub-sample of the 1,886 sections selected for the female sample.
The first Fertility Survey conducted by the INE was carried out in 1977. Since then, 4 editions have been carried out with non-regular periodicity.
The information collection method of this survey has been multichannel sequential. The main collection method has been that of a web-based interview (CAWI) completed by the respondent, which is complemented by a telephone interview (CATI) and a computer-assisted personal interview (CAPI).
The survey is addressed to a specific person, not to the dwelling, and nobody other than the selected person is allowed to respond (the interview ‘proxy’ was not accepted).
The information was collected over 15 weeks, from 12 March to 25 June 2018.
In all three cases, CAWI, CATI and CAPI, the questionnaire was electronic supported by a computer application, therefore it incorporates controls on range, flow, completion and validity that are in operation during the collection itself. In this way, most of the errors and inconsistencies can be filtered when the respondent is interviewed, since it incorporates warnings on minor inconsistencies or range errors that prevent the user from continuing until they are resolved.
Once the data has been received, a filtering application, developed by the Sub-directorate General for Information Technology and Communications (SGTIC), provides an exhaustive control of the data, analysing errors, serious inconsistencies, slight inconsistencies, extreme values, monitoring marginal distributions, crossing tables, etc. In addition, supplementary cross-checks are programmed or subsets of data are extracted to analyse specific variables.
In the first weeks of the information collection period, some serious errors were detected that allowed the electronic questionnaire to be improved. Errors also arose due to a misinterpretation of the questions which were corrected to some extent by transmitting them to the interviewers to be taken into account during the performance of their work, as well as to the operators of the 900 information and interviewee assistance line activated for the survey.
Likewise, during the entire collection, some invalid values and certain validation and range errors were detected in some questionnaires and corrected by re-contacting the respondent in 87% of the cases.
Once the data has been filtered, as explained in the previous section, the missing data is automatically imputed, applying the DIA program, based on the methodology by Fellegi & Holt. Exceptionally, in some cases, the correction of possible non-concordant or lost values has been carried out manually. All these works have been carried out by the corresponding unit of the SGTIC in close collaboration with the promoter service.
The next step is the calculation of the elevation factors, to determine the estimates of the different variables that are used in the survey, by the Sampling Unit of the INE.
Finally, the most significant tabulations of the survey are published, for which a comparison of the sample data with the population data and their analysis in order to check the sample's representation in relation to the variables used has previously been carried out. In the published tables, some cells for which the sample is considered to have been insufficient to collect this crossing of variables are blanked out, as a way of warning the user of the low quality of these data.
No adjustments are made