This presentation if for beginners in R and is geared toward use in psychometrics (academic, credentialing, and psychological exam development).

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.