A brief look at response to postal sifts, surveys and keeping in touch exercises from the viewpoint of the sampling implementation unit
2. General Mailing Procedures
In the majority of postal work the addresses are kept on a database. At present most postal work is conducted using the Postal Administration System (PAS) which resides on the VAX. The addresses reach the database either by a file transfer from the PAF, if a PAF based sample, or by the addresses being keyed by Data Prep, if a non PAF based sample. All addresses keyed by Data Prep require serial numbering by the SIU first.
The PAS allows for the production of address and serial number labels, address lists, reminder labels, reports and the production of a final sample if a sift is being used, plus the update of data where necessary.
The majority of postal work has two reminders sent. These reminders are despatched to all who have not replied, at intervals of two weeks. “Postals” are always despatched and returned by first class mail since a fast turn round is essential. Despatch normally takes place on a Thursday since the public seem to respond better if they receive the sift/questionnaire near to the weekend.
Some postal sifts and surveys have all non response follow up by interviewers calling. The SIU code the sift forms and Questionnaires to show the outcome using a different set of codes ot allow comparison of postal and interviewer response.
3.
Response
3.1 Toddlers Dietary Sift
Type: Postal Survey
Objective: To identify households with children aged 1.5 to 4.5 years of age by means of a one page sift document, asking age and sex of all those in the household. Source of sample: PAF based - clustered
Tracie Goodfellow Response to Postal Surveys Table 1 Toddlers Dietary Survey Postal Sift
Replies by wave and stage
WAVE Resp. to Orig M/O Resp. to 1st Rem Resp. to 2nd Rem Resp. to Int Call
No. % No. % No. % No. %
1 2,660 38% 1,127 16% 1,419 20% 1,794 26%
2 2,415 35% 1,520 22% 1,502 21% 1,563 22%
3 2,922 42% 1,604 23% 884 12% 1,590 23%
4 2,632 38% 1,422 20% 1,352 19% 1,594, 23%
Tot. 10,629 38% 5,673 20% 5,157 18% 6,541 23%
a) The base used for the calculations for each wave was the set sample of 7,000.
b) All postal response figures include: Completed Sift forms, Post Office (PO) returns, Refusals. c) The response to the interviewer call includes all non contacts, hence each wave totals 100%. d) M/O – Mail out.
Size: At each wave 7,000 addresses Timing: Wave 1 February – March 1992
Wave 2 May – June 1992
Wave 3 August – September 1992 Wave 4 November – December 1992 Reminders: Two at each wave, plus, interviewer follow up to non response
Points to Note;
a) Tables 1 and 2 show the response to this sift. b) The response at wave 1 was lower. This was a
direct result of the decision not to send a sift form with the first reminder. All other waves had sift forms sent at both reminder stages and the response increased markedly (See Table 1).
c) Wave 3 generated a much higher response to the postal at the original mail out and first reminder stages than all of the other waves., although the final response to the “postal” was similar to that experienced at waves 2 and 4 (See Table 2). This may have been due to the timing of this wave, although, other factors such as areas selected, can not be ruled out.
3.2 Day Care
Type: Postal Sift
Objective: To identify households containing children under the age of eight, using a one page
Table 2 Toddlers Dietary Survey Postal Sift
Positive response rates and non response rates
WAVE Post. Resp. Int. Resp. Non Resp. Total
No. % No. % No. % No. %
1 4,518 65% 1,150 16% 1,332 19% 7,000 100%
2 4,940 71% 1,007 14% 1,053 15% 7,000 100%
3 4,934 71% 984 14% 1,082 15% 7,000 100%
4 4,890 70% 900 13% 1,210 17% 7,000 100%
Tot. 19,282 69% 4,041 14% 4,677 17% 28,000 100%
a) Response = Completed sift form.
Tracie Goodfellow Response to Postal Surveys Table 3 Day Care Postal Sift
Replies by wave and stage
WAVE Resp. to Orig M/O Resp. to 1st Rem Resp. to 2nd Rem Resp. to Int Call
No. % No. % No. % No. %
1 13,080 48% 5,753 21% 5,510 9% 21,343 78%
2 4,712 49% 1,897 20% 897 9% 7,506 78%
Tot. 17,792 48% 7,650 21% 3,407 9% 28,849 78%
Figures quoted include: Completed Returns, PO Returns, Refusals.
sift document asking age and sex of members of the household. Source of sample PAF based sample – clustered Size: Initially 27,200 addresses
boosted by a further 9,600 Timing: July – September 1990
Reminders: Two postal reminders, on interviewer follow up to non response.
Points to note:
a) Sift questionnaires were mailed out with all reminders.
b) Response by post was higher than for the Toddlers’ sift; 78% were returned by post for this sift compared with 69% on the Toddler’s Survey. Response on the Toddlers’ sift was boosted by interviewer follow up.
3.3 nt Feeding, 1990 Great Britain sample
Type: Postal Survey
Objective: To collect information about experiences of infant feeding from mothers of babies at three stages from the age of six weeks to nine months, using a sixteen page questionnaire.
Source of sample: Draft Birth Registrations clustered by registration sub-districts or groups of sub-districts
Size: At stage one 9,064 births
At stage two 7,950 babies
At stage three 7,139 babies
Timing: Stage 1 October–
November 1990
Stage 2 January–February 1991
Stage 3 June – July 1991
Table 4 Infant Feeding Postal Survey, 1990 Great Britain sample Positive response rates and non response rates
STAGE Post. Resp. Int. Resp. Non Resp. Total
No. % No. % No. % No. %
1 7,150 79% 800 9% 1,114 12% 9,064 100%
2 6,336 80% 803 10% 811 10% 7,950 100%
3 5,577 78% - - 1,562 22% 7,139 100%
Tot. 19,063 80% 1,603 7% 3,487 14% 24,153 100%
Source: OPCS, 1990 infant Feeding Survey report a) Response = Completed questionnaire.
b) Non response = No baby, PO Returns, Refusals, no reply to interviewer/Postal, Non Contact by interviewer. c) Response rates are calculated on the set sample at each stage.
Tracie Goodfellow Response to Postal Surveys
Table 5 Children’s Dental Health Postal Survey
Replies by stage
Resp. to Orig M/O Resp. to 1st Rem Resp. to 2nd Rem Resp. to Int Call
No. % No. % No. % No. %
2,254 40% 1,328 23% 988 17% 1,096 19%
a) The base used for the calculations for each wave was the set sample of 5,666. b) All postal response figures include: Completed questionnaires, PO returns. Refusals. c) The response to the interviewer call includes all non contacts, hence each wave totals 100%.
Reminders: Two at each stage plus interviewer follow up to non response at stages 1 and 2 Points to note:
a) The sample declined over time due to refusals at each stage. However, the actual postal response remained fairly stable.
3.4 Children’s Dental Health
Type: Postal Survey
Objective: To collect background information about children who had been dentally examined in school, via a ten page questionnaire. Source of sample: Pupils on school registers in selected schools
Size: The set sample was 5,811, however, 145 dropped out of the sample because the school was told that the child had refused the dental examination or because the child had left school prior to the “postal”, hence, all figures are based on 5,666. Timing: February – March 1993
Reminders: Two plus interviewer follow up to non response
3.5 National Foundation for Educational Research
Type: Postal Survey – Personality Test
Objective: To collect completed
personality tests from a sample of adults. It was estimated that it would take about one hour for the test to be completed. Source of sample: Omnibus Survey, individuals
aged 16 – 64 selected by interviewer and who had responded to the Social Survey Division Omnibus Survey. The test was left with respondents who were asked to return it by post in a pre paid envelope. Size: 1,506 Timing: January – March 1993
Interviewer placement 18 – 28 January 1993
1st reminder despatched 18 February 1993
Table 6 Children’s Dental Health Postal Survey Positive response rates and non response rates
Post. Resp. Int. Resp. Non Resp. Total
No. % No. % No. % No. %
4,516 80% 682 12% 468 8% 5,666 100%
a) Response = Completed sift form.
Tracie Goodfellow Response to Postal Surveys
Table 7 NFER Postal Survey
Positive response by stage and non response
Resp. to left Qu. Resp. to 1st Rem Resp. to 2nd Rem Total Resp Total Non
Resp.
No. % No. % No. % No. % No. %
1,226 81% 61 4% 88 6% 1,375 91% 131 9%
a) Response = completed questionnaire b) All Non response were no replies.
2nd reminder despatched 4 March 1993
Reminders: Two but due to interviewer placement a longer time than normal was allowed between the placement and the first reminder.
Points to note:
a) A £5 incentive payment was offered to all who returned a completed questionnaire.
b) First contact was by interviewer who asked the Omnibus respondent if they would be willing to complete a further questionnaire. This meant that the element of ineligibility was ruled out and that those asked had already responded to the Omnibus Survey (80% of set sample responded to the Omnibus).
c) Further NFER surveys using the Omnibus as first contact will be carried out shortly without a £5 incentive payment although only to respondents in Non-Manual occupations. It will be interesting to see how response to these compares to the very high response rate achieved with the incentive payment.
3.6 Retirement Survey
Type: Keeping in touch exercise Objective: To keep in touch with a
sample of those aged 55 to 69 years of age who were interviewed on a survey of retirement plans. Each person was sent a one page questionnaire to complete. Source of sample: Originally postal sift, then
full interview
Size: Original follow up size 3543
Timing: Year 1 May – June 1991 Year 2 May – June 1992 Year 3 May – June 1993 Reminders: One
Points to note:
a) The 1993 survey is not yet complete, hence, response rates are only to date.
b) The number of movers found by this exercise was minimal at 14.
c) Between years some of the sample were lost due to deaths which were notified to the SIU largely by the National Health Service Central Register. The number of deaths on this survey were high due to the age of the population covered.
4. Summary
4.1 Postal Sifts
The Toddlers’ sift yielded a response rate of 69% on average of all of the 4 waves. This was boosted to 83% by the use of an interviewer follow up. There was an indication that response to the reminders was lowered if a further sift form was not included.
The Day Care sift, which had no interviewer follow up, achieved a response rate of 78%, however this figure includes PO returns and refusals.
4.2 Postal Surveys
The two postal surveys reported in this paper with 2 reminders and a questionnaire included at all stages but with no incentive payment yielded an average actual response rate of 80%.
Tracie Goodfellow Response to Postal Surveys Table 8 Retirement Keeping in Touch Exercise
Positive response by wave and stage
YEAR. Resp. to Orig M/O Resp. to 1st Rem Total Resp Total Non Resp.
No. % No. % No. % No. %
1991 2,087 59% 766 22% 2,853 81% 690 19%
1992 2,245 68% 444 13% 2,689 81% 621 19%
1993 1,941 63% 449 15% 2,390 78% 693 22%
a) Response = Completed form
b) Non response = PO Returns, Refusals, No reply to Postal, death.
The NFER yielded a 91% response rate which was considerably higher and was due to a combination of the fact that first contact was made by the interviewer and the fact that a £5 incentive payment on completion of the questionnaire.
4.3 Keeping in Touch Exercise
The total response with one reminder only is 81%. However, this is from an elderly population who tend to respond more quickly and readily. A similar
exercise with a younger population may vary considerably.
4.4 Future “Postals”
I hope to include a small paper in the next bulletin following up some of the issues raised in this paper and exploring the use of “postals” in constructing sampling frames.