To cite psychotree in publications use the references for the relevant functions/data sets:

If you use Bradley-Terry trees, bttree(), please cite:

Carolin Strobl, Florian Wickelmaier, Achim Zeileis (2011). Accounting for Individual Differences in Bradley-Terry Models by Means of Recursive Partitioning. Journal of Educational and Behavioral Statistics, 36(2), 135-153.<doi:10.3102/1076998609359791>

If you use Rasch trees, raschtree(), please cite:

Carolin Strobl, Julia Kopf, Achim Zeileis (2015). Rasch Trees: A New Method for Detecting Differential Item Functioning in the Rasch Model. Psychometrika, 80(2), 289-316.<doi:10.1007/s11336-013-9388-3>

If you use rating scale or partial credit trees, rstree()/pctree(), please cite:

Basil Komboz, Achim Zeileis, Carolin Strobl (2016). Tree-Based Global Model Tests for Polytomous Rasch Models. Educational and Psychological Measurement, forthcoming.

If you use MPT trees, mpttree(), please cite:

Florian Wickelmaier, Achim Zeileis (2016). Using Recursive Partitioning to Account for Parameter Heterogeneity in Multinomial Processing Tree Models. Working Paper 2016-26. Working Papers in Economics and Statistics, Research Platform Empirical and Experimental Economics, Universitaet Innsbruck. URL http://EconPapers.RePEc.org/RePEc:inn:wpaper:2016-26

If you use the SPIEGEL Studentenpisa data subsample, SPISA, please cite:

Sabine Trepte, Markus Verbeet (2010). Allgemeinbildung in Deutschland -- Erkenntnisse aus dem SPIEGEL Studentenpisa-Test. VS Verlag, Wiesbaden.

Corresponding BibTeX entries:

  @Article{,
    title = {Accounting for Individual Differences in {B}radley-{T}erry
      Models by Means of Recursive Partitioning},
    author = {Carolin Strobl and Florian Wickelmaier and Achim
      Zeileis},
    journal = {Journal of Educational and Behavioral Statistics},
    year = {2011},
    volume = {36},
    number = {2},
    pages = {135--153},
    doi = {10.3102/1076998609359791},
  }
  @Article{,
    title = {Rasch Trees: A New Method for Detecting Differential Item
      Functioning in the {R}asch Model},
    author = {Carolin Strobl and Julia Kopf and Achim Zeileis},
    journal = {Psychometrika},
    year = {2015},
    volume = {80},
    number = {2},
    pages = {289--316},
    doi = {10.1007/s11336-013-9388-3},
  }
  @Article{,
    title = {Tree-Based Global Model Tests for Polytomous {R}asch
      Models},
    author = {Basil Komboz and Achim Zeileis and Carolin Strobl},
    journal = {Educational and Psychological Measurement},
    year = {2016},
    note = {Forthcoming},
  }
  @TechReport{,
    title = {Using Recursive Partitioning to Account for Parameter
      Heterogeneity in Multinomial Processing Tree Models},
    author = {Florian Wickelmaier and Achim Zeileis},
    institution = {Working Papers in Economics and Statistics, Research
      Platform Empirical and Experimental Economics, Universit\"at
      Innsbruck},
    year = {2016},
    type = {Working Paper},
    number = {2016-26},
    month = {September},
    url = {http://EconPapers.RePEc.org/RePEc:inn:wpaper:2016-26},
  }
  @Book{,
    title = {{A}llgemeinbildung in {D}eutschland -- Erkenntnisse aus
      dem {SPIEGEL} {S}tudentenpisa-{T}est},
    editor = {Sabine Trepte and Markus Verbeet},
    year = {2010},
    publisher = {VS Verlag},
    address = {Wiesbaden},
  }