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Institut für Erziehungswissenschaft

Stella Sophia Bollmann

Stella Sophia Bollmann, Dr. phil.

  • Wissenschaftliche Mitarbeiterin / Academic Associate
+41 44 634 63 40
Kantonsschulstrasse 3, 8001 Zürich

Current Courses

V-Nr Lehrveranstaltung Beginn / Ende Termin Dozierende Raum

Research Interests

  • Latent variable models
  • Variable selection in multilevel data
  • Questionable research practices
  • Analysis of learning trajectories



  • 2016 Master of Science (M.Sc.) in Statistics, Ludwig-Maximilians-University Munich.
  • 2015 PhD in Psychology (Dr. phil), Ludwig-Maximilians-University Munich.
  • 2011 Diploma (Dipl.) in Psychology, Ludwig-Maximilians-University Munich.
  • 2005 Abitur, Leibniz-Gymnasium Altdorf bei Nürnberg.



  • Since 2023      Research Associate and project manager for PISA and ÜGK, Research Methods in Developmental and Educational Sciences, University of Zurich.
  • Since 2022      Postdoc, Methods for Developmental and Educational Sciences, University of Zurich.
  • 2020 – 2023    Statistical Consultant, Research and Development, University of Teacher Education Lucerne.
  • 2020 – 2021    Postdoc, Health Science and Medicine, University of Lucerne.
  • 2019 – 2022    President of the Swiss Statistical Society (SSS).
  • 2016 – 2019    Postdoc, Psychological Methods, Evaluation and Statistics, University of Zurich.
  • 2015 – 2016    Bavarian Equal Opportunities Sponsorship (BGF) 2015, Sponsorship for women in academia, Land of Bavaria, as postdoc.
  • 2013    Visiting Research Student (VRS), Department of Statistics, London School of Economics (LSE), 4 months.
  • 2013    Short-term scholarship for PhD students, German Academic Exchange Service (DAAD), as PhD student.
  • 2011 – 2016    Research Associate and Lecturer, Psychological Methods and Assessment, Prof. Dr. M. Bühner, Ludwig-Maximilians-University Munich.
  • 2008 - 2011    Student Assistant, Psychological Methods and Assessment, Ludwig-Maximilians-University Munich



Peer-reviewed publications

  • Bollmann, S., Groll, A., Havranek, M. (2023). Accounting for clustering in automated variable selection using hospital data: A comparison of different LASSO approaches. BMC Medical Research Methodology 23(1), 280.
  • Havranek, M., Ondrej, J., Widmer, P., Bollmann, S., Spika, S., Boes, S (2023). Using exogenous organizational and regional hospital attributes to explain differences in case-mix adjusted hospital costs. Health Economics.
  • Havranek, M., Ondrej, J., Bollmann, S., Widmer, P., Spika, S., Boes, S (2022). Identification and assessment of a comprehensive set of structural factors associated with hospital costs inSwitzerland. PLoS One, 17 (2): e0264212.
  • Götz, M., O’Boyle, E., Gonzalez-Mulé, E., Banks, G. & Bollmann, S. (2021). The "Goldilocks Zone": (Too) many confidence intervals in tests of mediation just exclude zero. Psychological Bulletin, (147), 95-114.
  • Bollmann, S., Berger, M., & Tutz, G. (2018). Item-Focussed Trees for the Detection of Differential Item Functioning in Partial Credit Models. Educational and Psychological Measurement, 78(5), 781-804.
  • Bollmann, S. (2018). Distributions. In B. B. Frey (Ed.), The SAGE encyclopedia of educational research, measurement, and Evaluation (Vol. 2, p. 540–544). SAGE Publications.
  • Bollmann, S. (2018). True-false items. In B. B. Frey (Ed.), The SAGE encyclopedia of educational research, measurement, and evaluation Vol. 4, p. 1728. SAGE Publications.
  • Bollmann, S. (2018). Exploratory factor analysis. In V. Zeigler-Hill & T. K. Shackelford (Ed.), Encyclopedia of personality and individual differences (p. 1-6). Springer International Publishing.
  • Bollmann, S., Cook, D., Dumas, J., Fox, J., Josse, J., Keyes, O., Strobl, C., Turner, H, & Debelak, R. (2017). A First Survey on the Diversity of the R Community. The R Journal, 9, 541-552.
  • Bollmann, S., Böbel, E., Heene, M., & Bühner, M. (2015). Which Person Variables Predict how People Benefit from True-False over Constructed Response Items? Psychological Test and Assessment Modeling, 57(2), 147-161.
  • Heene, M., Bollmann, S., & Bühner, M. (2014). Much ado About Nothing, or Much to do About Something? Journal of Individual Differences, 35(4), 245-249.


  • Bollmann, S. S., Prosperi, O., Kolovou, D., & Salvisberg, M., (2023). Mathematikbezogene Emotionen und Einstellungen In A. B. Erzinger, G. Pham, O. Prosperi, & M. Salvisberg (Eds.), PISA 2022: Die Schweiz im Fokus (pp. 35–43). University of Bern.
  • Havranek, M., Ondrej, J., Bollmann, S. (2020). Patientensicherheit und Wiedereintritte im Spiegel der medizinischen Statistik der Krankenhäuser.


  • Bollmann, S. (2016). Differential item functioning in partial credit models. Master thesis in statistics, Institute of Statistics, Ludwig Maximilians University Munich.
  • Bollmann, S. (2015). Vergleich von Methoden zur Strukturfindung in der Psychometrie mit Hilfe echter Daten. Dissertation in Psychology, Department of Psychology, Ludwig Maximilians University Munich.
  • Bollmann, S. (2011). The Influence of person variables on guessing success in true-false items. Diploma thesis, Department of Psychology, Ludwig Maximilians University Munich.