The Measurement Properties of Aggregated Relational Data and NSUM-Estimated Network Size.

Aggregated relational data (ARD), derived from questions of the form "How many people do you know who [belong to subpopulation X]?" are widely used to estimate the size and composition of social networks, often adopting the network scale-up method (NSUM). However, their measurement properties are insufficiently studied. The authors address this gap by assessing (1) the test-retest reliability of a large set of ARD questions and NSUM-estimated network sizes and (2) the convergent validity of these network size estimates. This mixed-methods study involved a heterogeneous quota sample of 50 citizens in Barcelona, Spain, in 2023. Respondents were interviewed twice over a 10- to 15-day period, answering a series of ARD questions on each occasion. Qualitative debriefing provided valuable insights into their response behaviors. Our findings indicate that NSUM accurately ranked respondents' network sizes but did not estimate their values consistently across measurements. Respondents gave lower answers in the second interview than in the first. In particular, the network sizes of people with large networks ("hubs") fluctuated significantly. NSUM-estimated network size moderately correlated with estimates from the summation method and Facebook friend counts. The authors discuss the implications and provide practical recommendations for ARD item selection and the use of NSUM instruments.