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The blog of the National Network of Libraries of Medicine Evaluation Office

Boosting Response Rates with Invitation Letters

"You've got mail" graphicwith mail spelled m@il

Today’s topic: The humble survey invitation letter.

I used to think of the invitation letter (or email) as a “questionnaire delivery device.”  You needed some way to get the URL to your prospective respondents, and the letter (or, more specifically, the email) was how you distributed the link. The invitation email was always an afterthought, hastily composed after the arduous process of developing the questionnaire itself.

Then I was introduced to Donald Dillman’s “Tailored Design Method” and learned that I needed to take as much care with the letter as I did the questionnaire. A carefully crafted invitation has been proven to boost response rates. And response rate is a key concern when conducting surveys, for reasons clearly articulated in this quote from the American Association of Public Opinion Research:

“A low cooperation or response rate does more damage in rendering a survey’s results questionable than a small sample, because there may be no valid way scientifically of inferring the characteristics of the population represented by the non-respondents.” (AAPOR, Best Practices for Research)

With response rate at stake, we need to pay attention to how we write and send out our invitation emails.

This blog post features my most-used tips for writing invitation emails, all of which are included in Internet, Phone, Mail, and Mixed-Mode Surveys: The Tailored Design Method by Dillman, Smyth, and Christian (2014). Now in its fourth edition, this book is the go-to resource for how to conduct all aspects of the survey process. It is evidence-based, drawing on an extensive body of research literature on survey practice.

Plan for Multiple Contacts

Don’t think “invitation email.”  Think “communication plan,” because Dillman et al. emphasized a need for multiple contacts with participants to elicit good response rates. The book outlines various mailing schedules, but you should plan for a minimum of four contacts:

  • A preliminary email message to let your participants know you will be sending them a questionnaire. (Do not include the questionnaire link)
  • An invitation email with a link to your questionnaire (2-3 days after preliminary letter)
  • A reminder notice, preferably only to those who have not responded (one week after the invitation email)
  • A final reminder notice, also specifically to those who have not responded (one week after the first reminder).

 Tell Them Why Their Feedback Matters

Emphasize how the participants’ feedback will help your organization improve services or programs. This simple request appeals to a common desire among humans to help others. If applicable, emphasize that you need their advice specifically because of their special experience or expertise. It is best to use mail merge to personalize your email messages, so that each participant is personally invited by name to submit their feedback.

If you are contacting people who have a relationships with your organization, such as your library users or members of your organization, play up that relationship. Also, make a commitment to share results with them at a later date. (And be sure to keep that commitment.)

Make Sure They Know Who’s Asking

With phishing and email scams abounding, people are leery about clicking on URLs if an email message seems “off” in any way. Make sure they know they can trust your invitation email and survey link. Take opportunities to publicize your institutional affiliation. Incorporate logos or letterhead into your emails, when possible.

Provide names, email addresses and phone numbers of one or two members of your evaluation team, so participants know who to contact with questions or to authenticate the source of the email request. You may never get a call, but they will feel better about answering questions if you give them convenient access to a member of the project team.

It is also helpful to get a public endorsement of your survey project from someone who is known and trusted by your participants.  You can ask someone influential in your organization to send out your preliminary letter on your behalf. Also you or your champion can publicize your project over social media channels or through organizational newsletters or blogs.

And How You Will Protect Their Information

Be explicit about who will have access to individual-level data and will know how they answered specific questions. Be sure you know the difference between anonymity (where no one knows what any given participant specifically said) and confidentiality (where identifiable comments are seen by a few specific people). You can also let them know how you will protect their identity, but don’t go overboard. Long explanations also can cast doubt on the trustworthiness of your invitation.

Provide Status Updates

While this may seem “so high school,” most of us want to act in a manner consistent with our peer group. So if you casually mention in reminder emails that you are getting great feedback from other respondents, you may motivate the late responders who want to match the behavior of their peers.

Gifts Work Better Than Promises

The research consistently shows that sending a small gift to everyone, with your preliminary or invitation letter, is more effective than promising an incentive to those who complete your questionnaire. If you are bothered by the thought of rewarding those who may never follow through, keep in mind that small tokens (worth $2-3) sent to all participants is the most cost effective practice involving incentives. More expensive gifts are generally no more influential than small gifts when it comes to response rates. Also, cash works better than gift cards or other nonmonetary incentives, even if the cash is of less value.

Beyond Invitation Letters

The emails in your survey projects are good tools for enhancing response rate, but questionnaire design also matters. Visual layout, item order, and wording also influence response rate. While questionnaire design is beyond the scope of today’s post, I recommend The Tailored Design Method to anyone who plans to conduct survey-based evaluation in the near future. The complete source is provided below.

Source: Dillman DA, Smyth JD, and Christian LM. Internet, Phone, Mail, and Mixed-Mode Surveys: The Tailored Design Method, 4th edition. Hoboken, NJ: Wiley; 2014.

 

 

 

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Last updated on Monday, June 27, 2016

Funded by the National Library of Medicine under Contract No. UG4LM012343 with the University of Washington.