This document discusses the benefits and challenges of combining multiple samples and modes in survey research. It notes that while telephone surveys appear resistant to bias despite low response rates, costs continue rising and response rates dropping. Common reasons for mixed method designs include using appended samples, listed samples with incomplete coverage, or selecting specific geographic subsamples. However, combining probability and nonprobability samples can increase systematic nonresponse and variability in bias. Using multiple modes also poses issues as different modes may produce different levels of measurement error. The document discusses various weighting and calibration methods that can help adjust for sample and nonresponse errors when combining samples and modes.
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