摘要：Objectives. We examined whether the widespread assumption that Hispanics are subject to greater noncoverage bias in landline telephone surveys because they are more likely than other ethnic groups to use cell phones exclusively was supported by data. Methods. Data came from the 2010 National Health Interview Survey and the 2009 California Health Interview Survey. We considered estimates derived from surveys of adults with landline telephones biased and compared them with findings for all adults. Noncoverage bias was the difference between them, examined separately for Hispanics and non-Hispanic Whites. Results. Differences in demographic and health characteristics between cell-only and landline users were larger for non-Hispanic Whites than Hispanics; cell usage was much higher for Hispanics than non-Hispanic Whites. The existence, pattern, and magnitude of noncoverage bias were comparable between the groups. Conclusions. We found no evidence to support a larger noncoverage bias for Hispanics than non-Hispanic Whites in landline telephone surveys. This finding should be considered in the design and interpretation of telephone surveys. The population trend of dropping landline telephone service and switching to cellular phones is a well-known threat to landline random-digit-dialed telephone surveys, in which cell phone numbers are not part of the sample. 1–6 According to the National Health Interview Survey (NHIS), the rate of cell-only usage for the US adult (aged ≥ 18 years) general population was 27.8% in the second half of 2010, more than double the rate in 2007 (12.6%). 7 This increasing cell-only usage implies that the proportion of the population without a landline telephone is much larger than when traditional landline random-digit-dialed surveys became popular in the 1970s. This decreases the proportion of the general population covered by the landline telephone frame, which is the listing of telephone numbers used to draw the samples. If we assume that those who have both cell and landline telephones but mostly use cell phones are difficult to reach over landline telephones, close to half of the adult population (45.2%) would be classified as unreachable via landline telephones. 7 Greater cell phone usage also implies greater noncoverage bias. As defined in literature, the noncoverage problem arises from failure to include some elements of the population in the frame. 8 Noncoverage bias is the difference in estimates derived from those who are covered by the frame and those who should be covered. It can also be calculated by multiplying the noncoverage rate and the difference between those who are covered and those who are not. For telephone surveys, bias may arise not only at the population level but also at the subpopulation level when the cell-only users are not accounted for in the data collection. 3,9 For example, for low-income young adults, ignoring cell-only users is likely to incur bias in health risk behavior variables, and for young adults in general, the estimates for alcohol consumption have been found to be subject to such noncoverage bias. 3,9 Besides age and lifestyle characteristics, ethnicity/race is considered to be an important correlate of telephone usage. The cell phone usage rates differ by ethnicity/race, and often non-Hispanic Whites report a lower cell-only rate than do other groups. Among minority groups, Hispanics are associated with the highest cell-only rate. 1,7,10 Figure A (available as a supplement to the online version of this article at http://www.ajph.org ) summarizes cell phone usage estimates for the adult general population, Hispanics, and non-Hispanic Whites from the 2008, 2009, and 2010 NHIS, as reported in Blumberg and Luke. 7 Hispanics consistently reported much higher cell-only and cell-mostly usage than the rest of the population. Their cell-only rate was close to 40%, and their combined cell-only and cell-mostly rate was higher than 55% in the second half of 2010, both about 13.4 percentage points higher than those of non-Hispanic Whites. The documented difference in cell phone usage leads many researchers to believe that noncoverage bias is larger for Hispanics than for other ethnic groups. However, this belief requires further investigation, because discussions about noncoverage bias need to address both noncoverage rates and differences between persons who are and are not covered by the frame. 8 Even with a high noncoverage rate, noncoverage bias may be trivial, if those who are covered by the frame are similar to those who are not. The reverse is also true. A low noncoverage rate does not guarantee low noncoverage bias. It is therefore essential to evaluate noncoverage bias rather than merely accounting for noncoverage rates. We examined potential noncoverage bias in landline telephone surveys for Hispanics by assessing their telephone usage and associated health characteristics. We further compared telephone usage and noncoverage bias between Hispanics and non-Hispanic Whites in 2 independent data sources.
