How Measurement Changes Can Exaggerate the Growth of Religious “Nones”

Academic and popular interest in nonreligion has risen in parallel with the growth of religiously unaffiliated populations. In many countries, census and survey questions used to measure religion have been modified to better capture nonreligious identities. Little attention has been given to how these changes in measures affect specific claims about the rise of the “nones.” Although there is no doubt that religiously unaffiliated populations have grown in many countries during the twenty- first century, the degree of such growth has sometimes been exaggerated due to measurement effects. We review methodological issues that affect the estimates of the size of religiously unaffiliated populations and their change over time. We call for further study to quantify the effect of these changes.