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Re-designing the German job vacancy survey ─ assessing the impact of high non-response rates
Hans Kiesl, Susanne Rässler
Institute for Employment Research (IAB), Germany
International Conference on Establishment Surveys IIIMontreal • June 18-21, 2007
2
Background
Information on job vacancies in Germany
Business units might report job vacancies to the Federal Employment Agency
Federal Employment Agency publishes monthly statistics on number of registered job vacancies (by industry class and NACE-sector)
IAB conducts a yearly (4th quarter) mail sample survey among business units to estimate number of job vacancies (registered or not) and to get additional information (e.g. about recruiting strategies)
Mail questionnaire (8 pages in length)
In the future: quarterly survey (CATI interviews in quarters 1-3)
3
Basic sampling design
stratified SRS; 16 sectors 7 size classes West/East
sampling rates and sample sizes in different size classes:
West East rate sample size rate sample size< 10 0.9% 11067 3.3% 10963
10 - 19 5.9% 8533 26.1% 9546
20 - 49 7.3% 6745 33.6% 8282
50 - 199 8.6% 4541 13.3% 1815
200 - 499 32.9% 3249 50.3% 1111
500 - 999 68.3% 1806 73.0% 395
>= 1000 75.1% 984 84.8% 193
total 2.4% 36925 8.0% 32305
4
Problem: extremely low response rates
0%
5%
10%
15%
20%
25%
30%
35%
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
5
Reasons for non-response
After 2004 survey, CATI subsample of non-respondents to find out main reasons for non-response
sample of 1700 business units
26% no/wrong telephone number
16% not willing to respond
58% respondents; their reasons for non-response in job vac. survey:
75%: no time; too much work (88% for largest units)
27%: no job vacancies (41% for smallest units)
25%: no relevant topic (44% for smallest units)
17%: take part in surveys only if mandatory
9%: never take part in surveys
6
Impact of length of questionnaire (1)
During the 4th quarter of 2006 (at the same time of the regular survey with 8 pages) a separate survey was conducted (1 page, basic infos, e.g. number of job vacancies).
Questions:
Has length of questionnaire significant impact on response rates? (Prediction: yes)
If so, do different response rates lead to different estimates of number of job vacancies? (Prediction: yes)
7
Impact of length of questionnaire (2)
Response rates by size of business units:
8 pages 1 page abs. diff. rel. diff.< 10 21.0% 27.3% + 6.3% + 29.9%
10 - 19 17.0% 30.7% + 13.7% + 80.1%
20 - 49 18.9% 28.2% + 9.3% + 49.1%
50 - 199 23.2% 28.6% + 5.4% + 23.2%
200 - 499 18.1% 27.1% + 9.0% + 49.9%
500 - 999 18.4% 28.5% + 10.1% + 54.9%
>= 1000 26.8%
8
Impact of length of questionnaire (3)
Response rates by sector:
8 pages 1 page abs. diff. rel. diff.Agriculture, farming, forestry, fishing 24.8% 36.5% + 11.6% + 46.9%
Manufacturing 19.6% 29.8% + 10.2% + 52.3%
Construction 21.5% 28.8% + 7.3% + 34.1%
Sale, trade, hotels and restaurants, transport, communications 14.9% 23.3% + 8.4% + 56.1%
Financial intermediation, insurance, renting and business activities 17.3% 24.9% + 7.6% + 44.0%
Public administration, education, health, social work, other service activities 23.0%
9
Weighting and estimation
Calibrate Horvitz-Thompson-estimator to totals from auxiliary data: sampling frame out of date (> 1 year)
up-to-date estimates on number of units by size and by sector (no
cross-classification)
up-to-date estimates on number of employees by size and sector (no
cross-classification)
registered number of job vacancies by sector
Previously: iterative proportional fitting with additional restriction
two different weighting factors within each stratum (units with and without job vacancies)
no variance estimation
Now: linear GREG
10
Effect on distribution of weighting factors
11
Impact of length of questionnaire on estimated number of job vacancies (1)
8 pages Standard error CV 1 page
West 775,000 29,000 3.7%
848,000 51,000 6.0%
East 212,000 10,000 4.7%
229,000 32,000 14.0%
Germany 987,000 31,000 3.1%
1,077,000 60,000 5.6%
12
Estimated number of job vacancies
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
< 10 10 - 19 20 - 49 50 - 199 200 - 499 500 - 999 >= 1000
8 pages1 page
Impact of length of questionnaire on estimated number of job vacancies (2)
13
Impact of length of questionnaire on estimated number of job vacancies (3)
Estimated number of job vacancies
0
50000
100000
150000
200000
250000
300000
350000
400000
450000
Agriculture,farming, forestry,
fishing
Manufacturing Construction Sale, trade,hotels and
restaurants,transport,
communications
Financialintermediation,
insurance,renting andbusinessactivities
Publicadministration,
education,health, socialwork, other
service activities
8 pages1 page
14
Conclusions
Length of questionnaire has considerable effect on response rates (as expected).
Change in response rates seem to have only little effect on main survey estimates (job vacancies) (not as expected).
Nevertheless split questionnaire design will be adopted in future.
Small-scale non-respondent CATI follow-up survey will be conducted every year.
Thank you very much for listening!
International Conference on Establishment Surveys IIIMontreal • June 18-21, 2007