The definitive study into how through the post questionnaires work appeared in the Journal of Marketing Research volume XII pages 440 to 453. In essence the findings of the paper "Mail surveys and response rates: A literature review" by L Kanuk and C Berenson of City University, New York, are these:

Preliminary Notification.   Advance notification that one is going to be involved in a questionnaire project can enhance response rates - especially where the advance notification is by telephone.   This is in keeping with the general finding in direct mail that a preliminary phone call can enhance response rates of all types.

Length of the questionnaire. There is no evidence to suggest short questionnaires get better response rates that long questionnaires.

Sponsorship.  There is little research on how the sponsorship of a questionnaire can affect the response rate, but the little research there is suggests that a well known and respected name can enhance response rates.

Return envelopes.  Amazingly there appears to be no research on the impact of putting a freepost envelope in with a questionnaire, although one survey did test the response rate of putting in a stamped addressed envelope, and found the response rate went up.  However some research has been done by Hamilton House (and this is not research conducted under university research conditions) which suggests that the way in which the return mechanism works depends on who is being questioned.  Consumers seem to respond more to the pre-paid envelope than businesses where the availability of the pre-paid envelope seems to make little difference.

Postage.  There was no noticeable difference to response rates between first and third class post, although response rates were higher when the questionnaire was posted via airmail or special delivery.

Personalisation.  All the research shows that no increase is gained in response rates when personalisation (or "mailmerging" as it is now known) is used.  This is completely in keeping with our own research projects on sales-orientated campaigns where mailmerge produces zero or negative results in most cases.  See the separate article on this for more information.

Cover Letters.  The American research was unable to find any studies on how the covering letter affected response rate, and so could draw no conclusion.  Our own research shows that the way in which a covering letter is written can have massive effects on response rates in mailings in general, so it would seem reasonable to assume that this is true in questionnaires as well.

Anonymity.  The researchers found that offering the respondents anonymity gave no increase in response rate - no matter how it was offered.

Size and colour.  Again there was no evidence found in the studies that the size, style of reproduction or the colour used had any effect on response rates.   The lack of impact of colour is interesting, and suggestive, when one considers the comments on colour made by its advocates (see the Factors article on colour - especially the final section).

Money incentive.  Small money incentives can help get questionnaires sent back very effectively.   In the 1970s experiments were undertaken using sums from 25 cents upwards, and all were effective.   One might assume that a 20p or 50p piece attached to the questionnaire would do the job well.

Deadlines were found to have no impact on response rate totals, but they did speed up the rate of return.

Differences between responders and non-responders.   As we might expect, the middle class person is more likely to respond than the working class person.

Followups.  Follow ups and reminders are almost univerally successful in increasing response rates.  As a result, they say, the well financed researcher can potentially achieve an extremely high total response rate.  But of course the cost of each new return increases as time goes by.

Research on line and via email.   This was obviously not covered in the original research survey quoted here, and I am not aware of any surveys done since.  But there has been a regular point made in research that data gathered on-line is much more unreliable than data provided in printed form.  The suggestion is that people filling in on-line feel anonymous, and often don't feel any relationship with the research - they just complete the form to get on a website, or because it is there.   Thus there is a tendency to tick any box that comes up, rather than laboriously flip through alternatives.   This I suspect is especially so on the ubiquitous question about where one is from.  When the UK falls at the bottom of the list it is much easier to tick Afghanistan at the top.

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This article is written by Tony Attwood, Chairman of Hamilton House Mailings Ltd.  If you would like to discuss the writing or design of your mailing campaign, or indeed a single mailshot, with Tony, without cost or obligation, just call 01536 399 000, or email Creative@hamilton-house.com   You can also send Tony a copy of your latest advert and he will call you back with his thoughts on how your response rate could be raised - again without cost or obligation.