On this page you will find a number of links to files containing syntax useful for researchers in the social sciences. The files will be in one of several formats (e.g., .txt, .sps). For instance, I have put together R functions useful in testing mediation and moderation (separately). These functions are only modestly documented with comments and are presented as a collection in a text document. I will, overtime, add to this page. Some of the R functions will eventually be packaged and documented with help files.
I have created these functions for use in my personal research as well as for three courses that I teach at the graduate level in the Department of Psychology at the University of Missouri - St. Louis.
Quantitative Methods II - A
comprehensive study of the use of multivariate statistics in data analysis.
Topics include the general linear model, multiple regression, factor
analysis, and multivariate analysis of variance.
Psychometric Theory - A consideration of classical and modern theories
of psychological testing. Topics include test reliability, validity, and
construction.
Quantitative Methods III - A
selective study of the use of multivariate statistics in data analysis.
Topics include structural equation modeling, multilevel modeling, and
analysis of longitudinal data.
I most frequently use the FREE program R ( www.r-project.org ) for most of my statistical operations. However, I make use of Excel ( www.microsoft.com ) and SPSS ( www.spss.com ) as well.
There are a number of authoritative introductions to using R and S-PLUS. I have put together a brief introduction. This is by no means comprehensive.
Data Screening is useful and often complex. ... I have put together a set of R functions to perform operations such as (1) convert a set of values to z scores, (2) assess both univariate and multivariate skewness and kurtosis, (3) graph basic univariate plots, among other things. This set of functions will be packaged and submitted to CRAN - the Comprehensive R Archive Network shortly.
Mediation occurs when the effect of an antecedent variable on a consequence is intervened by a mediating variable. One method for assessing mediation is through the product of the indirect paths. I have put together a set of R functions that correspond to a manuscript that was presented at Academy of Management. The functions assess both proximal and distal mediation. For distal mediation, that is mediation involving more than one mediator in a causal chain, all possible indirect effects plus the total indirect effect are returned. Functions are also created to assist in bootstrapping confidence intervals of various indirect effects.
Moderation occurs when the effect of one variable on another (X on Y) varies as a function of a third variable (Z). The component variables (X & Z) are said to interact with one another as they effect Y. I have put together a set of R functions that correspond to Aiken & West (1991) and Cohen, Cohen, West & Aiken (2003). The functions are useful in (1) testing interactions, (2) centering data, (3) testing simple slopes, and (4) graphing the effect of Y on X for two levels of Z (μZ ± 1 SD).
Applied Psychometric Theory is a package for R useful for basic item analysis, validity generalization, utility analysis and reliability estimation among other things. The set of functions correspond to the concepts and equations introduced in an introductory course in Psychometric theory at the graduate level. It is especially useful for I/O psychologists, but should be useful to all practitioners in the area of psychological measurement. The package is available for download from CRAN (Comprehensive R Archive Network). This package requires that you have R 2.3.0 or newer. The package also requires the installation of the package Multilevel (available from CRAN). The manual consisting of help files can be obtained in .pdf format here.
Instructional Videos - I have created (or will soon create) a series of videos that are useful in getting started with various software packages. For instance, I have created videos to demonstrate the use of R and Excel for basic issues such as basic matrix algebra in Excel, graphing in R, and how to obtain and enter useful functions in R. This set of videos will grow over the next few years based on student needs. Currently, the videos are password protected. This is just so that I can keep track of who is making use of them. If you are interested in viewing them, please send me an email. LINK to videos.
Thomas D. Fletcher, PhD
One University Blvd.
University of Missouri - St. Louis
St. Louis, MO 63121
Last updated: 12/20/06