The 2018 yearbook includes a selection of the more relevant data taken from the year's CIS barometers. The section "Perceptions about the economic and political situation" combines the core questions from the different barometers dealing with this subject - both from a retrospective and a prospective point of view. The "Assessment of the government and the opposition" section offers a review of respondents' assessments of the government, opposition, ministers and main political leaders in the political barometers usually conducted in January, April, July and October. Due to the unusual political situation in 2018, this section is structured differently to previous yearbooks: it includes series on the successive PP and PSOE governments and the tables and graphs have therefore been adapted to the questions and time points that existed then.

     The other sections represent a selection of the questions from each monthly theme. To this end, a balance has been sought between the relevance of each indicator and the number of questions chosen for that month. However, on occasion, the choice of certain sets of questions has necessitated more space.

     In presenting the data for each question, we have tried to maintain a similar structure in each chapter. Thus, the blocks on "Perceptions about the economic and political situation" and "Assessment of the government and the opposition" incorporate the annual longitudinal evolution of those opinions with a graph representing the responses, monthly or quarterly.

     The monthly themed blocks show the marginal frequencies (or averages, as the case may be) for each of the selected questions, also accompanied by a specific graph. In most cases, these graphs represent the percentage of each response option on an axis from 0% to 100%. However, for some specific questions - such as the average rating of political leaders and ministers - this representation has been adjusted to a scale with lower and upper limits that are close to the data in order to ensure its visibility (from 0 to 5), given the proximity of these values.

     For easier identification, a representative name has been assigned to the content of the tables included, referring to the month or themed block to which they belong. For example, the first table in the block "Perceptions about the economic and political situation" is called "SIT1 Table"; the first table in the block "Assessment about the government and the opposition" is labelled "POL1 Table"; the first table in the February barometer is called "F1 Table", and so on for the remaining months. These tables are a transcription of the question and response categories from the original questionnaire.

     Below are cross-reference tables showing variables that have the most common sociodemographic and political indicators offered by the CIS to its users: sex, age, marital status, education, employment situation, social class, ideology, voting record, religion and residential location. Some of the variables included have been re-coded, or transformed, for easier reading and interpretation of the data which are generally calculated for each category of the indicators mentioned (in row percentages). Only for some questions have these percentages been calculated by column and where this is the case, it is pointed out in the document.

      New for the 2018 yearbook is the inclusion of tables showing the results of two or three questions with complementary or similar content combined into a single table. For easier comparison, certain response options are shown, and alongside the percentage, the number of respondents (n). As with the 2017 yearbook, some annual time series are also included (continuously since 2003) from the chapter "Public opinion and fiscal policy".

      Age and social class variables keep the same categories that the CIS provides for the different surveys through its website. However, education, work situation, ideology, voting record, religion and habitat have been re-coded differently to present a more summarised table of results.

     Age incorporates the following ranges: up to 24, 25 to 34, 35 to 44, 45 to 54, 55 to 64, and 65 and over. Under the ideology variable, the mid-range values 5 and 6 have not been grouped. The other values have been grouped: on the left, the values 1-2 and 3-4; and on the right, the values 7-8 and 9-10.

     The tables in the chapter on "Public opinion and fiscal policy" also include the answer option "none", which was included in the 2018 barometer. The residential-location size categories have been classified as follows: places with fewer than 10,000 inhabitants as "small town or city"; 10,001 to 100,000 inhabitants as "medium city"; 100,001 to 1,000,000 inhabitants as "large city"; and over 1,000,000 inhabitants as "large population centre".

     In creating the education, social class and religion variables, a combination of questions has been used. For education, the question about whether or not someone attended school and the question that records their highest level of education are combined to create the following categories: "primary school or below", "lower secondary school", "middle school", "higher secondary school", "higher vocational training", and "university".

     The religion variable integrates the definition of religious matters with the frequency of religious practice, to create three categories: "practicing believer", "non-practicing believer", and "atheist, non-believer."

     With regard to voting record, the question of whether or not the respondent voted at the last election is combined with the question of which party they voted for. And for each month, the political parties and groupings standing at the previous election are taken into account. In this case, the parties that stood in the June 2016 general elections are used for reference.

son los partidos presentados en las elecciones generales de junio de 2016. Alongside the parties are the categories "wasn't old enough", "blank", "didn't vote", "doesn't remember", and "no response". The category "didn't vote" covers all options - including being prevented from or inhibited from voting under any of the two original questions (went to vote but couldn't do so, didn't go to vote because was unable to, preferred not to vote, and vote void). The option "wasn't entitled to vote" (reflecting a lack of voting rights) is not shown in the ranking.

     The social class variable is created from the responses given by respondents to three questions: employment situation, occupation and socioeconomic status, in accordance with Spain's National Classification of Occupations ("CNO") 2011 and Spain's National Classification of Economic Activities ("CNAE") 2009. The five categories for this variable are: "upper/upper-middle class" (includes professionals and technical specialists, managers and middle managers); "new middle classes" (non-manual employees); "old middle classes" (entrepreneurs, self-employed and farmers); "skilled workers" (skilled manual workers, foremen and craftsmen); "unskilled workers" (workers in industry and services; and agricultural labourers).

     The response categories "don't know (DK)" and "no response (NR)" for the explanatory variables are only shown in the tables in cases where this figure itself makes sense. Thus, "DK" and "NR" have been included when presenting political ideology; "doesn't remember" and "NR" under voting record; and "NR" under the religion variable. However in other cases (sex, age, marital status, education, employment situation and social class) they are not included due to their residual nature.

     In addition, where included in the design of the questionnaire, we specify whether this relates to a "Spontaneous response" on the part of the respondent when asked the question and, on other occasions, whether the interviewer was instructed not to offer it as a category for a predetermined response option - in which case "DO NOT READ" is shown next to that category. This is the situation with the "not applicable" category, which does not represent a response as such, but includes any situations where, due to the respondent's personal situation, the question does not apply.

     The fact that some of the categories for the different indicators do not feature strongly among respondents' responses, together with the fact that the total sample is distributed across the groups generated by stratifying the cross-over variables, forces us to highlight the limitations it imposes when interpreting the percentages. The number of people (n) who answer that question by category or as a whole is therefore shown in parentheses.

     The information provided for the selected questions is sometimes partial, for easier reading. Thus, for example, the response options "a lot" and "quite a lot" used in some sets of questions to capture both frequency and degree of agreement, have been grouped under the option "a lot + quite a lot" and the other response options ("a little" and "not at all") have been excluded. In other cases, response categories have been grouped where the result has been deemed relevant or for the purpose of summarising and facilitating comparison. This is the case, for example, with the question on "Guarantees for protecting personal data on the internet", where two response options ("very high + high") are grouped together.

     Generally, the aim is to present the most significant result for the type of question, so that, sometimes, only one piece of information is incorporated. This is the case with the chapter entitled "Public opinion and fiscal policy", where only the category "very few" is showing for the question relating to "Resources allocated to different public services".

     On the other hand, for questions that include the option of giving more than one answer (for example: first and second place), only the data referring to the first place are represented in the cross-reference tables. In addition, for 0 to 10 scales, when it is not part of a set of questions, the categories have been grouped for easier reading: 0-2, 3-4, 5, 6-7 and 8-10.

     Throughout the document there are multiple-choice questions that aggregate the answers given by the respondents to a list of options. Unlike the other questions, for these questions (n) represents the totality of answers instead of the totality of people who have answered. The interviewer marks all answers mentioned by the respondent, which means that the sum of the column percentages is greater than 100. At times, to make the table easier to read for multiple-choice questions, the most frequently mentioned answers are chosen - such as, for example, the question about "Ways of personally enjoying your main days off", where certain representative activities have been selected.

     The technical data sheets relating to each of the barometers in this yearbook can be found in an appendix.