Managing your invitation rate is half art and half science. Set your rate too high and you’ll hit your collection limit too early in the month; set it too low and you won’t meet your sample for the month.
We recommend checking out your historical data for an idea on invitation rate. On average, about 1-2% of visitors who receive the invitation and complete the survey. If you have 250 respondents per month and you assume a completion rate of 1%, you will need to invite 25,000 people. If your monthly (unique) traffic is 50,000, then you should set your invitation rate at 50% (25,000/50,000).
However, website visitor behavior differs from one site to the next. Lower engagement sites generally have a lower completion rate, whereas sites with a more engaged audience will have a higher completion rate. You will need to monitor your survey for the first few days to see if you’re over sampling or under sampling. Once you’ve established the average completion rate for your site, you should be able to set your invitation rate such that your sample is evenly distributed across the month.