Listed below are letters and other communications since 2009 explaining to institutions or organizations – with respect to the recipients’ own analyses of demographic differences, analyses by others that pertain to the recipients, or guidance on analyses of demographic differences that the recipients have given (or should give) to others – that most analyses of demographic differences regarding outcome rates are undermined by failure to recognize patterns by which measures tend to be affected by the prevalence of an outcome. Many items since 2012 are principally focused on the mistaken belief that generally reducing some adverse outcome will tend to reduce relative demographic differences in rates of experiencing the outcome (and the proportions more susceptible groups make up of persons experiencing the outcome) and explain that the opposite is the case. Recent treatments of the issues addressed in the communications may be found in “The Mismeasure of Health Disparities,” Journal of Public Health Management and Practice (July/Aug. 2016), “Race and Mortality Revisited,” Society (July/Aug. 2014), and “The Mismeasure of Health Disparities in Massachusetts and Less Affluent Places,” Methods Seminar, Department of Quantitative Health Sciences, University of Massachusetts Medical School (Nov. 18, 2015). A very recent treatment of the mistaken belief that generally reducing adverse criminal justice outcomes will tend to reduce relative racial/ethnic differences in rates of experiencing the outcomes, and the proportion racial/ethnic minorities make up of persons experience the outcomes, may be found in “United States Exports Its Most Profound Ignorance About Racial Disparities to the United Kingdom,” Federalist Society Blog (Nov. 2, 2017).