Presented by Assistant Professor Nalan Bastürk, Maastricht University (joint work with Suzanne van Bronswijk, Lotte Lemmens, Marcus Huibers and Frenk Peeters).


In applied psychological studies, data are often highly heterogeneous and the existence of latent subgroups of individuals is acknowledged. Recent challenges related to this heterogeneity are the determination of the correct number of subgroups by model-based clustering. The state-of-the-art models used for this purpose are prone to include too many subgroups due to overfitting, potential lack of robustness of the model specification and misleading results due to the use of continuous data models for count data collected as psychological indicators. We propose to use mixtures of Poisson distributions and Bayesian inference with weakly informative priors to assess such heterogeneity and to identify latent subgroups of individuals as descriptive step, for example prior to model based-clustering. We show that multiple modes in the estimated density for psychological indicators serve as indicators of heterogeneity and distinct subgroups in the data, and the use of proper and informative priors improve the obtained results. As a first step, we apply the mixture models to data from a recently conducted randomized trial, comparing the effectiveness of cognitive therapy and interpersonal psychotherapy for depression. We show that the obtained subgroups of individuals differ from conventional groupings in the literature and that individuals change between groups throughout treatment. The obtained results give valuable insights into the heterogeneity of the data and provide promising directions for time series models of these data, taking the count data properties into account. During this presentation, I will also outline a general research line on time series modeling of mental-health data, obtained from standardized depression measurement instruments.

About the presenter’s visit

Nalan Bastürk will be visiting the School of Economics on Thursday 5 December 2019.  While here he will be using room 520A Colin Clark Building.  If you would like to meet with him or have lunch or dinner with him please contact Professor Rodney Strachan who will be his host while at The University of Queensland.  Professor Strachan can be contacted on

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Room 105
Level 1, Colin Clark Building (#39)
UQ St Lucia