The polls are carried out on a monthly basis - except in August - and their main objective is to measure Spanish public opinion at that time. They involve interviews with around 2,500 randomly-chosen people from all over the country, with extensive social and demographic information on them being gathered for analysis as well as their opinions.
These studies include a block of set questions from which the “poll indicators are drawn up”. In addition to these, each poll contains another block of variable questions, which focus on a particular political or social issue on each occasion.
In January, April, July and October, the polls include a group of set questions on political attitudes, which the CIS uses to calculate and publish voting estimates.
The results of the monthly polls are made public on the CIS website, initially in “results preview format”. Once the other technical processes have been completed, including anonymisation, the study data are transferred to the CIS data bank, at which point the study microdata file can be downloaded from the web page along with the rest of the associated documentation.