SHARE data collection is based on computer-assisted personal interviewing (CAPI). The interviewers conduct face-to-face interviews using a laptop computer on which the CAPI instrument is installed. Personal interviews are necessary for SHARE because they make the execution of physical tests and the collection of biomarkers possible. Exceptions are the drop off and the vignettes questionnaires which are conducted via paper & pencil as well as the end-of-life interviews that can be conducted via CATI (computer-assisted telephone interview), too. For more details on SHARE data collection see the methodology of Börsch-Supan, A. and H. Jürges (2005).
An additional exception is the SHARE Corona Survey (see 4.11 for further details). Personal interviewing was not possible after the outbreak of the SARS-CoV2 pandemic. After careful considerations of the feasibility of different alternatives for SHARE’s target population, it was decided that SHARE would resume interviewing with a Computer-Assisted Telephone Interview (CATI).
The SHARE target population consists of all persons aged 50 years and over at the time of sampling who have their regular domicile in the respective SHARE country. A person is excluded if she or he is incarcerated, hospitalized or out of the country during the entire survey period, unable to speak the country’s language(s) or has moved to an unknown address. In Wave 1 all household members born 1954 or earlier, are eligible for an interview. Starting in the second wave, for new countries or refreshment samples, there is only one selected respondent per household who has to be born 1956 or earlier in wave 2, 1960 or earlier in wave 4, 1962 or earlier in wave 5, 1964 or earlier in wave 6, and 1966 or earlier in wave 7. In addition – in all waves – current partners living in the same household are interviewed regardless of their age.
All SHARE respondents who were interviewed in any previous wave are part of the longitudinal sample. If they have a new partner living in the household, the new partner is eligible for an interview as well, regardless of age. Age eligible respondents who participated are traced and re-interviewed if they move within the country and end-of-life interviews are conducted if they decease. Younger partners, new partners and partners who never participated in SHARE will not be traced and are not eligible for an end-of-life interview.
In order to save time and reduce the respondents' interview burden, the CAPI main questionnaire is designed in a way that not every eligible household member is asked every questionnaire module. Household respondents answer questions on housing, household income and consumption representative for all household members. On behalf of the couple, financial respondents answer financial transfer and asset questions and family respondents answer questions on children and social support – also on behalf of the couple. The respondent types are indicated by the variables hou_resp (household respondent), fin_resp (financial respondent) and fam_resp (family respondent) in the cv_r module as well as in the technical variables module. The SHARELIFE questionnaire does not differentiate between respondent types.
If physical and/or cognitive limitations make it too difficult for a respondent to complete the interview her-/himself it is possible that the sample respondent is assisted by a so-called proxy respondent to complete the interview (“partly proxy” interview). If the proxy respondent answers the entire questionnaire in lieu of the respondent, the interview is referred to as a “fully proxy” interview. Examples of conditions under which proxy interviewing is allowed are hearing loss, speaking problems, Alzheimer´s disease and difficulties in concentrating for the whole interview time period. Proxy respondents are also asked for end-of-life interviews in case of a respondent´s decease. Some questionnaire modules are defined as non-proxy sections because those cannot be answered by other persons. Cognitive functioning, mental health (partly), grip strength, walking speed, activities, and expectations modules are non-proxy sections. The other sections contain the information on who answered the section at the end of the respective questionnaire module: (1) respondent only, (2) respondent and proxy or (3) proxy only.
Depending on the available sampling frame, some countries might need a screening procedure to determine the eligibility status of the respondents while others need no initial screening. Based on this differentiation, there are several ways in which final response rates can be calculated, depending on how cases of unknown eligibility are handled (see AAPOR guidelines for further information):
|I:||number of completed interviews|
|P:||number of partial interviews|
|R:||number of refusals and break-offs|
|NC:||number of non-contacts|
|O:||number of other non-interviews|
|UH:||number of cases with unknown eligibility (unknown if housing unit exists)|
|UO:||number of cases with unknown eligibility (unknown, other)|
|e:||fraction of eligible units among the cases with known eligibility|
Further information on the calculation as well as the final response rates in SHARE on household and individual level by wave, country, and certain subgroups can be found in this Technical Paper.
After several waves, various types of retention rates can be calculated conditional on previous participation that might differ between countries due to differences in the sample composition. In SHARE we differentiate between the following concepts:
- Individual-level retention excluding recovery
- Individual-level retention including recovery of former respondents
- Individual-level retention including recovery of former respondents and new/missing partners
More detailed information about the participation of respondents in their first (baseline/refreshment) interview and the longitudinal development of the survey including response and retention rates can be found in this Technical Paper.
Sample attrition means that respondents drop out from the survey over time. The reasons for the drop-out can be multifarious. For a longitudinal sample which was drawn randomly at the beginning of the data collection process, sample attrition would not pose any challenges if the attrition occurs randomly – which is not the case in reality. Besides refreshing the sample in several countries (which is also dependent on funding) the strategy of SHARE to deal with problems of sample attrition is to dedicate special effort into re-interviewing respondents who participated in previous waves and to provide calibrated weights. Under certain conditions, these weights may help to reduce the potential selectivity bias generated by sample attrition and unit nonresponse.
SHARE makes every effort to interview and recover (panel) respondents, and is quite successful in that (see recovery rates in Bergmann et al., 2019, section 5). However, after several waves of non-participation, the chance to recover any more respondents from households that did not participate for a very long time is negligibly low. Furthermore, a high percentage of unpromising cases is demotivating for interviewers and can affect the overall wave response/retention rates and the fieldwork quality. Since Wave 7, we therefore apply sample cleaning rules similar to most other large panel studies.
Sample cleaning rules in SHARE:
- Households in which none of the eligible members has participated in three or more consecutive waves are dropped from the longitudinal sample. Non-participation can be either non-contact, refusal, unknown address or any other justified reason.
- Eligible individual sample members who have deceased and where it was not possible to find a proxy conducting an end-of-life interview for two waves or longer are dropped from the longitudinal sample.
SHARE classifies the vital status of respondents as either “alive”, “dead” or “unknown”. Note that due to the lack of a national mortality register in most European countries, we cannot reliably ascertain the vital status of non-respondents. More information can be found in this Technical Paper.
Survey data can cover a wide range of topics. However, a survey cannot cover all topics of interest and information provided by respondents could be incomplete or inaccurate. Administrative data is more accurate but usually limited to a certain topic. Linking survey data with administrative data is a way to combine the best of both worlds. Upon respondents’ written consent, administrative data of the German Pension Fund can be linked to the survey data of the German subsample of SHARE (SHARE-RV). Similar linkage projects have been set up in other SHARE countries as well: Austria, Belgium, Estonia, Denmark, Finland, the province of Girona in Spain, Luxembourg and the Netherlands. For more information on this project see question 6.3.
The SHARE study is subject to continuous ethics review. During Waves 1 to 4, SHARE was reviewed and approved by the Ethics Committee of the University of Mannheim. Wave 4 and the continuation of the project were reviewed and approved by the Ethics Council of the Max Planck Society. In addition, the country implementations of SHARE were reviewed and approved by the respective ethics committees or institutional review boards whenever this was required. The numerous reviews covered all aspects of the SHARE study, including sub-projects and confirmed the project to be compliant with the relevant legal norms and that the project and its procedures agree with international ethical standards. Please see overview and summary of the ethics approvals for more information.