Click, collect, compare: Evaluating a nonprobability web survey for family demography

Background: High-quality population data are expensive to collect and limited in substantive scope, constraining timely and innovative research. Objective: We evaluate nonprobability data from the KINMATRIX survey by comparing it with external data on kinship structure and relationships to kin. Methods: KINMATRIX is a web-based quota survey of over 12,000 younger adults (aged 25–35) in 9 European countries and the United States. Respondents reported egocentric kinship networks, yielding more than 250,000 ego–kin dyads. We compare indicators in three domains – family network size (number of living kin), family relationships (emotional closeness, geographical distance, coresidence, and contact frequency), and family complexity (parental separation and number of half-siblings) – with estimates from probability-based surveys, demographic projections based on official vital statistics, and national registers. Results: KINMATRIX estimates of family network size tend to be lower than demographic projections based on official data, with smaller gaps for aunts and uncles and larger gaps for siblings and cousins. Cross-national differences in the number of parents, siblings, aunts, uncles, and cousins are broadly consistent across data sources, whereas patterns differ for grandparents. Regarding family relationships, the correspondence between KINMATRIX and probability surveys varies across indicators, but established north–south contrasts are generally preserved. Regarding family complexity, KINMATRIX yields lower rates of parental separation than probability-based data, but it broadly captures cross-national differences. Contribution: Our comparisons point to nonprobability data having both promise and pitfalls in family demography, highlighting the need for study-specific benchmarking and targeted validation.