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- 1. D I A N E T A L L E Y U N I V E R S I T Y O F N O R T H C A R O L I N A , C H A P E L H I L L R Programming for Psychometrics Presented to Alpine Testing Solutions August 2013
- 2. Define R/perceptions of R R in psychometrics What’s great and not so great about R Legal defensibility and R Learning R The R environment A few tips for beginners
- 3. What is R? Implementation of the S statistical programing language (Bell Labs -Chambers, Wilkes, Becker) Developed at University of Auckland by professors Robert Gentleman and Ross Ihaka http://www.r-project.org/contributors.html - lists all R contributors An object oriented language…..sort of
- 4. The R Community: Perceptions from without and within R is for hippies! …(Quote from a SAS user) …or perhaps nerds with a quirky sense of humor using words such as Cran-tastic, Cranberries, and useRs
- 5. The R Community Oh, and all the pirate jokes! “R Matey”
- 6. But seriously, what is R? It has an academic following and data analytics across industries (i.e., pharma, biostats). The commercialized side of R: Data Analytics Revolution Analytics Enterprise software Possibly the SAS Enterprise version of R
- 7. How is R being used in Psychometrics I’m using the term psychometrics in reference to the field of testing (educational, credentialing, and psychology) Research See references Mostly using simulated data and related to the use of a particular r package (i.e., eRm for Rasch modeling) Test delivery The Psychometric Centre at Cambridge University Concerto http://www.psychometrics.cam.ac.uk/page/338/concerto-testing- platform.htm What about use in practice? There’s not much evidence yet that I have found indicating R is being used to construct examinations for high stakes testing purposes.
- 8. Benefits It’s free! Runs on multiple platforms (Windows, Unix, MacOS) Validation/replication of analyses (assumes commented code and documentation) Long term efficiency (using the same code for multiple projects)
- 9. Psychometric Capabilities CTT IRT Factor Analysis Scoring Test delivery (Concerto) Survey analysis Database access
- 10. Drawbacks Perceptions (as they pertain to using R for high stakes testing purposes) Open source could be a problem for use with high stakes testing projects…maybe Challenging to learn (some say R is one of the hardest programming languages to learn) http://www.statmethods.net/about/learningcurve.html http://datakeyword.blogspot.com/2012/10/analysis-tools-comparison-r- language.html
- 11. R is free software and comes with ABSOLUTELY NO WARRANTY. What does that mean for use in psychometric practice? Or for any practice for that matter.
- 12. R and Legal Defensibility Is the open source nature of R an issue for legal defensibility?
- 13. Learning to Program in R
- 14. Books For a comprehensive list go to http://www.r- project.org/doc/bib/R-books.html Field, A., Miles, J., & Field, Z. (2012). Discovering statistics using R. London: Sage Publications Ltd . This is great for learning how to use R in the context of statistical tests, unless you are sensitive to Dr. Field’s non-pc sense of humor. Pace, L. (2012). Beginning R: An introduction to statistical programming. New York: Apress. These two are great reference books to have on the shelf: Teetor, P. (2011). R cookbook. Sebastopol, CA: O'Reilly. Teetor, P. (2013). R graphics cookbook . Sebastopol, CA: O'Reilly.
- 15. Free Online R Tutorials http://www.statmethods.net/ Quick R – This was one of my favorites for getting started. https://www.coursera.org/course/compdata There’s a course starting in September taught by a professor at John’s Hopkins University http://ww2.coastal.edu/kingw/statistics/R-tutorials/ http://tryr.codeschool.com/ Beware the pirate humor! http://r-statistics.net/r-tutorial.html http://www.personality-project.org/r/book/ http://www.computerworld.com/s/article/9239625/Beginner_s_gui de_to_R_Introduction http://decisionstats.com/2013/07/18/datamind-a-new-effort-to- teach-r-online-for-free- rstats/?goback=.gde_77616_member_259229553 Heavily focused on data analytics in R
- 16. R Training for a Price http://georgia-r- school.org/?goback=.gmr_77616.gde_77616_member_20182 0973 • Online only http://www.revolutionanalytics.com/ • Instructor led training and online (through stats.com) • Path available that leads to a credential
- 17. User Groups and Blogs That I Like LinkedIn R Project for Statistical Computing Most friendly to new users who are asking basic questions. http://www.r-bloggers.com http://www.foastat.org/ http://planetr.stderr.org/ http://stackoverflow.com/ This is the best I’ve found for technical questions
- 18. Associations FOA – Foundation for Open-Analytic Statistics Promoting methodology and software that allows truly reproducible research Free online journal http://eeecon.uibk.ac.at/psychoco/ Psychometric computing
- 19. Conventions and best practices No official best practices Google’s R Style Guide is helpful When in doubt use rseek.org (this is google with an R filter – hugely helpful!)
- 20. The R Environment
- 21. Installing R http://cran.r-project.org/ Technical docs - http://developer.r-project.org/ Latest release 3.0.1 Mirrors - R isn’t housed in a single location, but across the globe at mirror sites. Pick the one nearest you. Task View This is an amazing reference. Packages are organized by purpose (i.e., Social Sciences, Psychometrics, Graphics). Updates You can install new version without uninstalling old version. Haven’t found an answer to the question of whether you should do this. Internet based R, if you prefer http://roncloud.com –
- 22. Installing Packages Base packages Psych packages http://cran.r-project.org/web/views/ Install once, call each time you need to use it library() require() Or, if you are using an IDE such as Rstudio it’s as simple as checking a box Masking - Learn what it is and pay attention to it!
- 23. Programming Environments Basic R Some free IDEs Rstudio (My personal preference) - http://www.rstudio.com/ide/docs/using/source Architect - http://www.openanalytics.eu/downloads RevolutionR - http://www.revolutionanalytics.com/downloads/ Revolution Analytics has 3 versions, a “community” version that is free and two that are not free
- 24. Some Psychometric Packages to Start With CTT psych psychometric ggplot2 equate plyr eRM mirt sem
- 25. Getting Help R manual library(help="stats") Package documentation and vignettes rseek.org
- 26. A note about graphs and tables Graphs graphics is part of basic R ggplot2 is recommended by many users and books Tables: It’s not pretty if you are doing this using psych packages! I’m sure there’s a way to make an APA table, but I haven’t found it yet. Applications that allow you to create reports (pdf, word, LaTeX) Sweave knitr
- 27. Writing an R program
- 28. Objects and Functions object <- function (formal arguments) Example 1 rawScores <- c(26, 42, 36, 49) Example 2 mean(rawScores) Is this all you need to know?
- 29. Functions, Classes, and Object-Oriented Programming http://developer.r-project.org/ Chambers, J. (2006) How S4 methods work. Retrieved from http://developer.r-project.org/howMethodsWork.pdf August 1, 2013 This is a good description of how classes, methods, objects, and functions work. It also explains how R is different from other OO languages such as Java and C++. Venables, W. N., (2009). An introduction to R. United Kingdom: Network Theory Limited. (Also avaible online at http://www.cran.r-project.org/doc/manuals/R-intro.pdf)
- 30. A few things to note… naming objects (i.e., rawScores, raw.scores) Keep them simple Start with letter, not a number Don’t use underscores or spaces Don’t begin with caps Don’t replicate (we’ll come back to this) R users don’t like loops. Use apply() in the plyr package – although some disagree attach() Popular opinion is NOT to use attach. This gets to the problem of masking if you have two objects with the same name and you attach them both, which is being called by your program?
- 31. Psychometrics in R – Related Research Chalmers, R. P. (2012). mirt: A multidimensional item response theory package for the R environment. Journal of Statistical Software, 48(6), 1-29. Debelak, R., & Tran, U. S. (2013). Principal component analysis of smoothed tetrachoric correlation matrices as a measure of dimensionality. Educational and Psychological Measurement, 73(1), 63-77. De Leeuw, J., & Mair, P. (2007). An introduction to the special volume of “psychometrics in R.” Journal of Statistical Software, 20(1), 1-5. Epskamp, S., Cramer, A. O. J., Waldrop, L. J., Schmittmann, V. D., & Borsboom, D. (2012). qgraph: Network visualizations of relationships in psychometric data. Journal of Statistical Software, 48(4), 1-18.
- 32. More References Fox, J. P., Entink, R. K., & van der Linden, W. (2007). Modeling of responses and response times with the package cirt. Journal of Statistical Software, 20(7), 1-14. Frick, H., Strobl, C., Leisch, F., & Zeileis, A. (2012). Flexible Rasch mixture models with package psychomix. Journal of Statistical Software, 48(7), 1-25. Hatzinger, R., & Dittrich, R.(2012). prefmod: An R package for modeling preferences based on paired comparisons, rankings, or ratings. Journal of Statistical Software, 48(10), 1-31. Mair, P., & Hatzinger, R. (2007). Extended Rasch modeling: The eRm package for the application of IRT models in R. Journal of statistical software, 20(9), 1- 20.
- 33. More References Monecke, A., & Leisch, F. (2012). semPLS: Structural equation modeling using partial least squares. Journal of statistical software, 48(3), 1-32. Rosseel, Y. (2012). lavaan: An R package for structural equation modeling. Journal of Statistical software, 48(2), 1-36. Verhelst, N. D., Hatzinger, R., & Mair, P. (2007). The Rasch sampler. Journal of Statistical Software, 20(4), 1-14. Weeks, J. P. (2010). plink: An R package for linking mixed-format tests using irt- based methods. Journal of Statistical Software, 35(12), 1-33. Wickelmaier, Fl., Strobl, C., & Zeileis, A. (2012). Psychoco: Psychometric computing in R. Journal of Statistical software, 48(1), 1-5.
- 34. One Final Comment R really is a community of users in support of a common cause. I have found a great deal of passion and dedication in its users and a strong desire to help others in the common pursuit of good research. Ask questions, but be respectful of the community and research your problems/questions before you ask them.

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