Has Conservative Judaism's reported sharp decline from 40% to 27% of American Jewish adults between 1990-2000 been accurately measured? Critical analysis of three national surveys reveals serious methodological flaws undermining this widely-cited finding. By comparing response rates across national Jewish population surveys conducted in 1971, 1990, and 2000, this research exposes a dramatic deterioration in data quality - from a robust 79% response rate in 1971 to just 29% in 2000. Statistical analysis demonstrates that the 2000 survey's exceptionally low participation introduces substantial nonresponse bias, potentially increasing total survey error by at least seven times the reported sampling error. Given these severe methodological limitations, the claimed one-third decline in Conservative movement affiliation cannot be reliably accepted. To restore scientific validity in future national Jewish population surveys, significant improvements are needed, including face-to-face interviewing, partnership with university-based research organizations, and enhanced community engagement strategies to achieve adequate response rates for meaningful conclusions.