1 1 Effects of attrition in the Norwegian Survey on statistics on income and living conditions Marit Wilhelmsen Statistics Norway Q European Conference on Quality in Official Statistics, Helsinki, Finland 4-6 May 2010

2 Effects of attrition in the EU-slic The response rate has been declining over recent years. What are the known background characteristics of the people that participate? How severe is the extent of attrition in the EU-silc? Is attrition influenced by the same characteristics as non response? Do attrition lead to increased survey bias, introduced in the first wave?

3 Background The sample units are persons aged 16 or more registered in the central population register (inhabitants). A rotational design was chosen to ensure both cross- sectional and longitudinal data. This design rotate a part of the sample form one year to the next retaining the other part unchanged. The sample units are asked to participate eight years in a row. Each year 1/8 of the sample will be replaced. We look the group drawn in 2003 and follow it until (n = 1066) We follow the respondent from the first wave T1 in (n= 731)

4 Response rate in the EU-Silc

5 Attrition in the Eu-silc Response rate for participants in T1 (2003) in

6 Education in T1 (2003) and response rate in

7 Income in T1 (2003) and response rate in 2004 – 2008

8 Logistic regression. Interviewed in Dependent variable: Interview in 2008

9 Concluding remarks To some extent attrition follows the same pattern as non response in the first wave. Education and young age matter if you participate or not Difficult to conclude if attrition leads to increased survey bias that where introduced in the first wave. Probably there are other unknown factors that decide if you participate or not, that might not be as selective Recruitment in the first wave is the most important factor for further recruitment in the survey.

10 Thank you for your attention