Unweighted base size
The unweighted base is the number of people who were asked a specific question.
Weighted base size
To ensure that the sample used is as closely representative of the full population as possible YouGov "weights" each respondent to make up for a slight discrepancy between our panel and general population. These weights are calculated such that respondents belonging to an under-represented demographic are weighted higher than respondents belonging to an over-represented demographic, and so that the weighted proportions for the demographic variables in the dataset the weighting targets.