One approach that might fit here is similar to what he calls "Double Sampling", which is basically to email the 30 that didn't respond, and even if you get something like 5-10 responses back, you can use that smaller sample to roughly represent the entire 30 that didn't respond. Not perfect (this will increase the error bars for your survey results), but nothing in survey design is.
A few other options are also offered, such as taking a much smaller representative sample, but somehow forcing 100% participation (possibly do-able in some circumstances) to help provide a gradient for the whole population, including those who didn't respond to the initial survey.
I was contacted for the Swiss labor market survey and ignored that because I was very busy with other things (business, baby, etc.) It required multiple extended phone interviews.
They followed up and emphasised that they take the experiment very seriously and that my answers would be considered representative of 500 people in Switzerland, notionally all juggling the same priorities as me.
I was very impressed at the seriousness and made time to take the survey.
One approach that might fit here is similar to what he calls "Double Sampling", which is basically to email the 30 that didn't respond, and even if you get something like 5-10 responses back, you can use that smaller sample to roughly represent the entire 30 that didn't respond. Not perfect (this will increase the error bars for your survey results), but nothing in survey design is.
A few other options are also offered, such as taking a much smaller representative sample, but somehow forcing 100% participation (possibly do-able in some circumstances) to help provide a gradient for the whole population, including those who didn't respond to the initial survey.