The Effect of Questionnaire Length on Response Rates and Level of Estimates in the German Job...

The Effect of Questionnaire Length on Response Rates and Level of Estimates in the German Job Vacancy Survey

Hans Kiesl

Institute for Employment Research (IAB), Germany

Q2008 – European Conference on Quality in Official Statistics

Rome • July 9-11, 2008

2

Background

Regulation (EC) No. 453/2008 of the European Parliament and of the

Council of 23 April 2008 on quarterly statistics on Community job

vacancies

Member states have to provide quarterly data on job vacancies (broken down to NACE section level) quality reports

In Germany, the data will be provided by the IAB.

3

Background (2)

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 NACE-sector)

Since 1989, IAB conducts a yearly (4th quarter) 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); voluntary

CATI interviews in quarters 1 - 3

4

Basic sampling design

stratified SRS; 16 sectors 7 size classes x West/East

sampling rates and sample sizes in different size classes (IV/2006):

  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

5

Highly skewed distribution of job vacancies0

100

200

300

400

job

vaca

ncie

s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

6

Highly skewed distribution of job vacancies0

20

40

60

80

100

job v

acancie

s

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

91 88 84 76 72 68 86 89 88 84 78 77 81 87 83 87% of Zeros:

7

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 2007

8

Reasons for non-response

After fall 2007 survey, CATI sub-sample of non-respondents to

find out main reasons for non-response

sample of 1292 business units

6% no/wrong telephone number or late respondents

15% not willing to respond

79% respondents; their reasons for non-response in job vac. survey:

54%: no time; too much work (72% for largest units)

20%: no job vacancies (25% for smallest units)

4%: no relevant topic (44% for smallest units)

7%: take part in surveys only if mandatory

7%: never take part in surveys

9

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; 9,450 sampling units).

Research 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)

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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%      

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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%      

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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

Linear GREG, using CLAN (Statistics Sweden)

Results quite robust with regard to underlying model

e.g. constant variance or variance proportional to (1 + number of registered vacancies)

13

Impact of length of questionnaire on estimated number of job vacancies (1)

  8 pagesestimated

standard error estimated cv

  1 page    

West 791,000 27,000 3.4%

  843,000 51,000 6.0%

East 212,000 10,000 4.7%

  229,000 32,000 14.0%

Germany 1,003,000 30,000 3.0%

  1,072,000 60,000 5.6%

(Note: differences to officially published results due to slightly different weighting)

14

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 pages

1 page

Impact of length of questionnaire on estimated number of job vacancies (2)

15

Impact of length of questionnaire on estimated number of job vacancies (2)

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 pages

1 page

16

Impact of length of questionnaire on estimated number of job vacancies (3)

    8 pages 1 page

     (higher

response)

weighting without number of registered vacancies 211,000 256,000

registered job number of vacancies 529,000 676,000

vacancies share of registered vacancies 40% 38%

  number of units with vacancies 166,000 176,000

weighting with      

registered job number of registered vacancies 465,000 465,000

vacancies number of vacancies 791,000 843,000

  share of registered vacancies 59% 55%  number of units with vacancies 172,000 199,000

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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).

Indication that non-response bias might be only modest.

Thank you very much for your attention!

Q2008 – European Conference on Quality in Official Statistics

Rome • July 9-11, 2008