A magazine publisher is informed that 72% of subscribers last year did not renew their subscriptions. This publisher wants to randomly survey 8% of these past subscribers asking the reason why they did not renew their subscriptions. All of last year's subscribers who did not renew their subscriptions are known collectively as what

Sampling frame

Explanation:

A sampling frame is the source where the researcher draws his samples from. In other words, a sampling frame is like the population where the researcher gets samples for his investigation. In the above example, we are told the researcher wants to know why the 72% that subscribed last year didn't subscribe this year. He draws a sample of 8% from the 72% that he is trying to study, therefore the 72% are the sampling frame from where he gets his sample.