1. Presentation of the Groningen group plan Marijtje van Duijn ECRP Meeting Ljubljana, Feb. 2, 2012

2. Who is (who?) in Groningen Marijtje van Duijn Christian Steglich Christophe Stadtfeld Tom Snijders Mark Huisman Filip Agneessens …

3. What do we do – for ECRP? Statistics, models, methods, simulation/computing, applications … ECRP project: Peer Influence in Social Networks: Comparing and Evaluating Methods across Domains. Focused on influence – and disentangling it from selection (contagion vs. homophily)

4. Influence vs. selection Hot topic! Requirements – Longitudinal data – Adequate statistical model/method SAOM; network autocorrelation; GEE; SEM; … Why difficult? (interesting!) – Results seem to depend on model used – Adequacy of model assumptions Not straightforward in longitudinal social network data No ‘independent’ observations … Lots of debate

5. The Groningen contribution Comparing and evaluating method Two dimensions 1.Models (used for the analysis) 2.Data (and their properties) SAOM (RSiena) is the starting/reference point – Analysis – Data generation Simulation studies – Aimed at comparison of models/methods

6. General purpose of a simulation study Show that (estimation) method works well Generate data according to model Estimate model parameters Show that these are ‘good’ (unbiased, etc.) Show that model estimation is sensitive to assumption violation and/or misspecification Generate ‘wrong’ data Use ‘wrong’ model for estimation Evaluate estimation resuls

7. Rough design of ECRP simulation study Generate data and analyze it with – the ‘true’ model and – other ‘wrong’ models – Compare the results of both analyses Works for SAOM (can do both) More difficult for other models/methods – E.g. GEE has implicit way of controlling for dependence in the network data How use it for data generation? What are true parameter values? – What are realistic parameter choices, i.e. leading to plausible network data (structures)

8. Input from/output to other projects Other projects may provide interesting and realistic data configurations – For our data generating Our methods may be useful for other projects – Advice for choosing analysis method – For analysis of your data Great for collaboration!

9. Why now (and not earlier)? Interesting question… Some possible answers – Focus on model development (as a start) – Various approaches to model development (different groups; working on similar problems; with different modeling solutions) – Now that models have been developed, a wider view is possible – …???

10. First start Christoph’s presentation tomorrow Questions and suggestions …???