## The Annals of Applied Statistics

- Ann. Appl. Stat.
- Volume 9, Number 3 (2015), 1247-1277.

### Estimating population size using the network scale up method

Rachael Maltiel, Adrian E. Raftery, Tyler H. McCormick, and Aaron J. Baraff

#### Abstract

We develop methods for estimating the size of hard-to-reach populations from data collected using network-based questions on standard surveys. Such data arise by asking respondents how many people they know in a specific group (e.g., people named Michael, intravenous drug users). The Network Scale up Method (NSUM) is a tool for producing population size estimates using these indirect measures of respondents’ networks. Killworth et al. [*Soc. Netw.* **20** (1998a) 23–50, *Evaluation Review* **22** (1998b) 289–308] proposed maximum likelihood estimators of population size for a fixed effects model in which respondents’ degrees or personal network sizes are treated as fixed. We extend this by treating personal network sizes as random effects, yielding principled statements of uncertainty. This allows us to generalize the model to account for variation in people’s propensity to know people in particular subgroups (barrier effects), such as their tendency to know people like themselves, as well as their lack of awareness of or reluctance to acknowledge their contacts’ group memberships (transmission bias). NSUM estimates also suffer from recall bias, in which respondents tend to underestimate the number of members of larger groups that they know, and conversely for smaller groups. We propose a data-driven adjustment method to deal with this. Our methods perform well in simulation studies, generating improved estimates and calibrated uncertainty intervals, as well as in back estimates of real sample data. We apply them to data from a study of HIV/AIDS prevalence in Curitiba, Brazil. Our results show that when transmission bias is present, external information about its likely extent can greatly improve the estimates. The methods are implemented in the NSUM R package.

#### Article information

**Source**

Ann. Appl. Stat., Volume 9, Number 3 (2015), 1247-1277.

**Dates**

Received: August 2013

Revised: December 2014

First available in Project Euclid: 2 November 2015

**Permanent link to this document**

https://projecteuclid.org/euclid.aoas/1446488738

**Digital Object Identifier**

doi:10.1214/15-AOAS827

**Mathematical Reviews number (MathSciNet)**

MR3418722

**Zentralblatt MATH identifier**

06525985

**Keywords**

Aggregated relational data barrier effect HIV/AIDS recall bias social network transmission bias

#### Citation

Maltiel, Rachael; Raftery, Adrian E.; McCormick, Tyler H.; Baraff, Aaron J. Estimating population size using the network scale up method. Ann. Appl. Stat. 9 (2015), no. 3, 1247--1277. doi:10.1214/15-AOAS827. https://projecteuclid.org/euclid.aoas/1446488738