A report form AAPOR filed by Collen Carlin.
Another cloudy, rainy day here at AAPOR in New Orleans and another day of cell phone discussions to attend. Yesterday we heard further evidence that the cell phone only population is growing and today there was information on the changes to this population and ways to include cell-only people in a study in a more efficient manner.
The folks at U of M and Gallup used the Gallup panel (itself RDD – landline recruited) to conduct a mail/web study to examine the characteristics of people who had recently switched to cell-only (within the last year) to those people who made this switch prior to that time period. The results indicate that those who made the switch to cell only recently tend to be older, married, and living in the Midwest when compared to those who have been cell only longer. Conclusions are that the demographics of the cell only population maybe shifting away from the young, urban, lower income people that we previously knew to comprise this group.
Next up was a study done by the folks at CBS that was akin to the work Mitofsky and Waksberg did to develop the method for RDD. If we accept that the cell only group is creeping into a greater proportion of the population we need to investigate ways to include this group that are more economical. The authors took a list of known cell phone, known non-cell phone and undetermined cell phone numbers and added +45 to the digit within the 100 number blocks. The purpose was to determine if there are 100 blocks of numbers with higher proportions of working cell phone numbers, much as we find with landline numbers. This allows us to more efficiently target working telephone numbers within an RDD method. For the numbers that were modified from the known cell phone and undetermined numbers, approximately 75 percent were determined to be working cell phone numbers, 20 percent were non-working and 4 percent were unknown. The numbers from the known non-working cell phone group that were modified yielded 42 percent working cell phone, 58 percent non-working cell and 0 percent unknown numbers. The numbers in the same 100 block as the known working cell phone numbers were significantly more likely to also be working cell phone numbers, but non-working cell phone numbers did not necessarily denote an entirely bad number block. If we need to start including cell phone numbers in our telephone surveys than it is useful to know ways to more efficiently target these numbers.
Results from another study presented explored the relationship between those people who intend to switch to cell only within the next year and those people who have gone cell only already. This small study found similarities within these groups which could provide some information for weighting purposes.