Christopher Jencks’ New York Review of Books article, “Why the Very Poor Have Become Poorer” is based on surveys and, as Jenks inadvertently acknowledges, surveys produce unreliable information; that is, information that may or may not be correct. For example, the Census Bureau’s Survey of Income and Program Participation (SIPP), produces “more income” per family “than . . . other Census surveys”. And even though SIPP estimates are higher than estimates from other Census surveys, “SIPP estimates” may be “too low”. Thus, estimates that are high may also be low. Jencks does not, because he cannot, tell us which high or low estimate is correct or incorrect. Like others who rely on survey research, Jencks just reports the conflicting information and fits it into his narrative. Survey researchers and those who rely on survey research have blatant disregard for consistency.
Jencks’ article exemplifies one of the major weaknesses of surveys: different surveys of the same topic (in this case, family income) produce different results.
For more information about the fatal flaws of survey research, see my book, The Problem with Survey Research.