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Panel Effects in the American National Election Studies Bartels, Larry M. Uploaded 07-11-1998 Keywords panel attrition panel conditioning fractional pooling two-stage auxiliary instrumental variables American National Election Studies Abstract Parallel panel and fresh cross-section samples in recent NES surveys provide valuable leverage for assessing the magnitude of biases in statistical analyses of survey data due to panel attrition and panel conditioning. My analysis employing a variety of typical regression models suggests that, on average, panel biases reduce the inferential value of panel data by about ten percent. Biases in individual coefficients are rarely statistically "significant," even when panel and cross-section respondents have markedly different characteristics. Thus, while I propose adjustments for panel effects in both cross-sectional and dynamic analyses, such adjustments are unlikely to be necessary in typical applications using NES or similar data