A report from AAPOR filed by Colleen Carlin:
At 10 am this morning in the cloudy city of New Orleans a packed crowd of survey enthusiasts gathered in a small room, all waiting to hear ‘the number’. ‘The number’ refers to the estimate put out twice a year by Stephen Blumburg and associates from the National Interview Health Survey. The NIHS is a large scale, face-to-face survey that includes questions about telephone usage. It has been invaluable in helping to estimate the percentage of cell only households in the United States.
The estimate from the last six months of 2007 is that 14.5 percent of adults (more than 32 million people) are wireless only; this is up from 12.6 percent for the first 6 months of 2007. If you prefer to think of things in terms of households the number is 15.8 percent. This means that nearly one out of every six homes in American is only reachable through a wireless telephone. As survey practitioners who rely heavily on telephone methodologies this number poses an increasing problem. But wait… it gets worse. There is now a group of people termed ‘wireless mostly’ that we need to worry about. These are the people who have a both a landline and cellular telephone, but who receive all or almost all calls on their cellular phones. I have a good friend from school that recently got married, had a child and bought a house. As a survey practitioner I was thrilled to hear that she had converted from one of those nasty ‘wireless only’ households into a dual cell and landline household upon purchasing her first home. My elation ended when I tried to call her on her landline one day. After several unsuccessful attempts to reach her I finally tried her cell phone. She told me that she stopped answering her landline after the first few weeks due to the frequent sales calls she receives at that number. Instead she uses her landline only for out-going calls when she is at home. According to the numbers from the NIHS 22.3 percent of households with both cellular phone and landlines are considered ‘wireless mostly’. These people are nearly as difficult (although not impossible) to reach in a RDD survey as wireless only people. Blumburg estimates anywhere from 16.4-30.4 percent of the adult population can not be contacted by a non-cell phone number.
One suggestion proposed to deal with this issue is through post survey adjustments. Can we try to account for wireless only people by using the estimates from those wireless mostly people who can be reached by landline? Results from wireless only respondents were compared to wireless mostly and everyone else. For most of the demographic and health variables the wireless mostly respondents were more similar to the wireless only people then the rest of the population. In other words, while the numbers didn’t match up exactly they were moving in the right direction. It is possible that wireless mostly respondents who can be reached by a landline could represent the wireless only people in a phone survey. It is also possible that the wireless mostly adults who respond to a landline survey might be more similar to others with landlines than to the wireless only population, meaning they would not be a good proxy. As with all things survey related, more research is needed.