The negative values -21 -20, -11, -10, -9, -8, -7, -2, -1 have been reserved for different types of missing data. Other than these values any negative value represent actual value of the variable.
The value -1 means that the respondent said they didn’t know the answer to this question and -2 means they refused to answer the question. The value of -8 means the respondent was not asked this question as they were not eligible. For example, only those who say they are currently employed are asked questions about their current employment. So, for others the value of these variables will be -8. The value -9 is reserved for non-specific reasons of missing value such as coding error.
A value of -7 is assigned for questions not asked of the proxy respondents. Sometimes when a person refuses to complete the adult interview, they may agree that someone else (generally their adult children or spouse or partner who is expected to know about them) answer the questions on their behalf. These proxy interview questionnaires are shorter and only include factual information that someone else may know about the sample member. So, if a question is not included in the proxy questionnaire, the value of that variable for the proxy respondent will be -7.
There are additional negative values set aside for missingness relevant in specific files. In the xwavedat file, -20 means “no data from BHPS” and -21 means “no data from Understanding Society”. In Wave 6, some questions were asked of the new IEMB sample and not the other samples (GPS, EMBS, BHPS samples) while it was the other way round for some questions. The differences in these two sets of questionnaires are available here. But as the data collected in Wave 6 from all samples are provided in one set of datafiles, missing values of -11 and -10 are provided to reflect this type of missingness. So, only in Wave 6 data files -11 means “variable not available for non-IEMB samples” and -10 means “variable not available for IEMB sample”.
