There have been several researchers that examined whether there is a
difference in response between first class postage versus bulk rate. A
meta-analysis of these studies revealed a small, but significant,
aggregate difference of 1.8 percent. Envelopes with bulk mail permits
might be perceived as "junk mail", unimportant, or less personal, and
thus will be reflected in a lower response rates.
A few researchers have also examined whether metered
mail or stamps work better on the outgoing envelope. The
results of these studies suggest a small increase in
response favoring a stamped envelope. A meta-analysis of
these studies revealed that the aggregate difference was
slightly less than one percent.
Many researchers have reported increased response
rates by using registered, certified, or special delivery
mail to send the questionnaire. The wisdom of using these
techniques must be weighed against the consequences of
angering respondents that make a special trip to the post
office, only to find a questionnaire.
It is not clear whether a typed or hand-addressed
envelope affects response. One study, conducted at the
University of Minnesota, reported that students responded
better to hand-addressed postcards, while professors
responded better to typed addresses.
This writer could find no studies that examined
whether gummed labels would have a deleterious effect on
response rate, although we might predict that response
rate would be less for gummed labels because they have
the appearance of less personalization.
This writer could also find no studies that examined
whether the color of the envelope affects response rate.
First impressions are important, and the respondent's
first impression of the study usually comes from the
envelope containing the survey. Therefore, we might
predict that color would have a positive impact on
response because of its uniqueness.