Considering the income question

Deciding whether or not to ask an income question was a critical step in the development of the 2011 Census questionnaire.

The 2007 Census Test included questions about the sources and level of each person’s income. Around 100,000 households were asked to participate in the test. Approximately half of these received questionnaires that included the income questions; the rest received questionnaires with no income questions.

The test evaluation included an assessment of the effect of the income questions on response rates, field operations, the public view of the census and the quality of the data obtained from these questions.

The case for inclusion

Four key findings supported the inclusion of an income level question in the 2011 Census:

1. Around 90.9 per cent of individuals who submitted valid responses to the 2007 Test also completed the income level question, even though it was the last question asked on the questionnaire

2. The inclusion of the income questions did not affect the item response rates to the other questions. This is consistent with findings from the Northern Ireland Statistics and Research Agency's (NISRA) 2007 Census Test in Northern Ireland, General Register Office Scotland's (GROS) 2006 Census Test in Scotland, and the 1997 Test taken in Great Britain

3. The inclusion of the income questions did not result in additional individuals contacting the Census Contact Centre regarding these questions

4. The inclusion of the income questions did not have a negative impact on the coverage of individuals within households

The case for exclusion

Five key findings supported the exclusion of an income level question:

1. The overall response rate for questionnaires with no income questions was 53.3 per cent whereas the response rate for income questionnaires was 50.6 per cent - a statistically significant difference of 2.7 percentage points, which is consistent with findings from the 1997 Test. This indicates that more households would need to be followed up for non-return of questionnaires if income questions were included in the 2011 Census

2. Individuals who were unemployed, over 65 years of age, less qualified, from certain ethnic minority backgrounds, living in local authorities identified as generally low income areas, or females tended to report lower income and had lower item response rates to the income level question than comparison groups

3. A total of 404 individuals who completed the 2007 Test income level question also took part in the Census Test Evaluation Survey (CTES), in which they were asked this question again. Responses matched in only 66.8 per cent of cases, indicating that the question was difficult to answer. This is consistent with findings from NISRA’s 2007 Test

4. There was evidence that individuals who submitted valid 2007 Test responses had concerns about the income questions. More than half of those who did not answer the income level question did answer the ethnic identity or qualifications questions

5. Many newspapers took a negative stance in their reporting of the inclusion of income questions in the 2007 Test and proposals to include such questions in the 2011 Census