1) Survey design: The objectives, universe, sample and questionnaire.
2) Data collection or field work
5) Results publication: How are the results of CIS surveys disseminated?
The aims of the survey: What topics does the CIS research?
To begin to carry out a survey, it is necessary to define its aims: On which topic or topics do we want to learn the public's attitudes and opinions.
The CIS aims to gain a deeper knowledge of the attitudes and behaviour of Spanish society, and to measure its degree of stability and/or change over time. Since it was founded, it has taken nearly 2,000 surveys on widely ranging topics.
The definition of the universe (population of interest) and sample selection: Who is asked to answer the survey?
The survey universe is the population from which we want to obtain information. The population at whom CIS surveys are generally addressed holds Spanish nationality and is over 18 years of age, but sometimes they are addressed at the entire population residing in Spain (and they therefore include residents from abroad). It also carries out surveys where the universe is the young population (generally defined as that aged between 15 and 29) or some other subgroup of the population.
Given that it is impossible to interview the whole of the population, it is necessary to make a selection, take a sample of people on whom the survey will be taken. The CIS follows the necessary scientific procedures to obtain representative samples. It is crucial that these procedures be observed in order to be able to use the data obtained in the survey to describe and analyse the population from which the sample has been taken, always bearing in mind that there is always a margin of error (the size of which appears on each survey fact sheet).
Although the size and characteristics of the sample vary according to the aims of the survey, CIS surveys usually take a minimum sample of 2,500 individuals.
The writing of the questionnaire: How are the questions asked?
The questionnaires are made up of a series of questions which enable it to gather the public's opinions on different topics. In the case of the CIS, they are largely of a social and political nature. They furthermore include questions on the characteristics of the persons being interviewed (sex, age, level of qualifications, occupation), given that one of the aims is to learn whether there are differences in the opinions in each of those groups. Survey data files do not hold any information that can identify the people that have taken part in them.
CIS technical staff draw up the questionnaires based on thorough documentation which includes consultation of previous studies performed in the CIS and in other institutions, as well as those designed by international bodies devoted to carrying out surveys.
When designing the questions, special care is placed on them being understood by all the persons interviewed, irrespective of their level of qualifications or any other characteristic. Special care is also taken that they be balanced and not contain any kind of bias.
In most of the questions asked by the CIS, the answer options appear on the questionnaire and they are given a numerical code, which is what is recorded on the data file.
There are other questions on the questionnaire which are open, with no preset answer options, such as, that included in all the CIS monthly barometers, which asks the persons interviewed to express, in their own words, what they believe are Spain's three main problems. All these responses are then subsequently classified in the CIS in what is termed the “codification process”. It is thus possible to group together all those referring to “unemployment”, “housing”, “immigration”, in order to be able to count up the number of mentions each of these topics receives.
La recogida de datos –llamada también “trabajo de campo”- consiste en la aplicación de un mismo cuestionario de preguntas a todas las personas seleccionadas. En la actualidad, el CIS recoge los datos de encuesta a través de entrevistas telefónicas, aunque ocasionalmente puede realizar entrevistas presenciales en el domicilio de la persona entrevistada.
Si la encuesta es telefónica, las entrevistadoras y entrevistadores llamarán a teléfonos móviles y fijos con la ayuda de una aplicación que genera números aleatorios; cuando realizan las llamadas no tienen ninguna información sobre a quién ni a dónde están llamando; por esa razón, al contactar con una persona se pregunta sobre el sexo y la edad y el municipio al que se está llamando, con el fin de comprobar si cumple con las características que requiere la muestra diseñada.
Si la encuesta es presencial, en el domicilio, entrevistadoras y entrevistadores acreditadas/os recorren las secciones censales –calles y números predeterminados- que se han extraído al azar para la muestra y contactan con los ciudadanos/as en sus casas con el fin de recoger su opinión sobre el tema de la encuesta.
La colaboración de las personas seleccionadas es siempre voluntaria pero fundamental para conseguir que los resultados de la investigación reflejen con rigor las opiniones del conjunto de la sociedad.
La encuesta no es un examen y no hay respuestas correctas o erróneas, lo que buscamos es la opinión sincera sobre un tema. En cualquier momento, la persona entrevistada puede elegir no contestar a una pregunta si así lo desea.
Todas las respuestas son anónimas y están protegidas por las leyes de secreto estadístico y de protección de datos de carácter personal. La información recogida se utiliza de manera agregada, sin referencias individuales. No se conserva ningún dato personal que pueda identificar a una persona concreta.
El CIS realiza labores de supervisión e inspección del proceso de realización de las entrevistas para garantizar la calidad de los datos que recoge. Por este motivo, en el caso de las entrevistas telefónicas, la conversación será grabada; si la entrevista se ha realizado personalmente en el domicilio de la persona entrevistada, las/os entrevistadoras/es le pedirán un número de teléfono para poder comprobar que efectivamente se ha realizado la entrevista a dicha persona.
Si usted desea verificar la extensión desde la que el CIS le ha llamado, puede llamar a los siguientes números de teléfono, donde se le informará del estudio que se está llevando a cabo y se verificará la extensión telefónica desde donde se le ha llamado.
Once the data collection process has concluded, all the information obtained from the answers to the questionnaires is processed.
In order to learn the results and analyse public opinion on the subject of the survey, the information obtained has to be recorded. The answers the interviewees give to each question on a survey are converted into a data file or matrix structure.
In the files, each row corresponds to one questionnaire (one interviewee) and the columns contain each of the questions they have been asked. The specific answer that the interview has given to question on the questionnaire is put in the intersection of the row and column. The end file never contains information that could identify the interviewee.
Structure of a data file
| Questionnaire no. | Province | Municipality | Gender | Age | No. of children | Appraisal of the economic situation | Appraisal of state education (0-10) | Appraisal of the work done by teachers | Degree to which you agree with the contents of the Organic Law on Education |
| 0001 | Murcia | Ojós | Male | 18 | 0 | So-so | 3 | So-so | Totally agree |
| 0002 | Barcelona | Masnou | Female | 78 | 2 | Bad | 6 | Bad | Partially agree |
| 0003 | Badajoz | Mérida | Female | 45 | 2 | Bad | 7 | Good | Does not know |
| ... | |||||||||
| ... | |||||||||
| 2499 | |||||||||
| 2500 | Zaragoza | Calatayud | Male | 32 | 1 | Good | 5 | Good |
The information recorded on the data files provides the survey results.
The CIS presents the results of its surveys both in documents that contain the data already processed and the matrices or files on which the data is recorded.
a) Documents that contain the data already processed (or tabulated):
Initially, a provisional version of these documents is presented on the CIS website, in documents called “results previews”.
Subsequently, a thorough review of all the data is carried out to detect any possible error before the files becomes part of the CIS Data Bank. Once all the data has been reviewed and the verification, purging and anonymisation process has been performed, the study goes into the CIS Data Bank and the data file is then available to the public. The Law that regulates CIS operations stipulates specific deadlines for each of these steps, depending on the type of survey that has been performed.
b) Data files or matrices, showing all the answers given by interviewees, once the purging, validation and anonymisation process has been carried out
People who want to make an in-depth analysis of the results of a survey usually use the data file, as this enables them to cross any kind of information (questions), or, for example, in the case of surveys containing information on voting intention, to try to make different estimates of election results.
c) Technical documentation: