If your survey is lengthy, so long that it might deter some invitees from taking part, consider doing a two-step survey. The first survey gathers most of the data you would like to have; for those who respond to it, you send them a shorter survey that drills down on some points or adds the additional questions.

Once someone has invested the time to submit a completed survey, they are revealed to believe that the topic and findings are worth their effort. They evidence commitment. It may well be they are engaged enough with the subject of the survey to take another step.

I have written that it is a good practice to respond to each participant with an email that at the least thanks them for doing so. Such a tailored message can also encourage them to proceed with a second step. You don’t have to create a second online survey with a link to it in your thank-you email. In a throw-back, retro move, you could ask a few questions in the email. That will force you to extract the answers manually, but it is a delegable task, and you may only have a smallish number to deal with. Alternatively, you can wait until you have enough respondents that it makes sense to bulk-email them all with your follow-on inquiries.

When I have done such a two-step method, several benefits become clear. It lets me learn from the answers to the earlier surveys and refine the drill-down survey. I can gently inquire about new areas to explore. The back and forth increases my marketing contacts. The second step builds rapport with my respondents as I touch them again with what may appear to be a more personal, follow up survey. Notably, I ask them about colleagues or peers in their metropolitan area. The canned response capability of Gmail makes this much easier.

Someday, hosting software may be able to take the answer to a question on the first survey and trigger the sending of a second, shorter survey. Not just a conditional question but a second survey entirely. I have not found such an extension, yet, but it has promise.