# Jeromy Anglim's Blog: Psychology and Statistics

## Monday, May 24, 2010

### Great Measurement but Small Sample Size: Case Study of Videotaped Families

New York Times reports on an interesting UCLA study that involved video taping 32 Los Angeles families over the course of a week. The study generated rich data for analysis. It's great to see researchers moving beyond self-report measures towards real-world well-coded behavioural observations. However, great measurement does not overcome issues of a small sample size.

## Thursday, May 20, 2010

### Inverting a Logistic Function

I was recently talking to a researcher who had conducted a cognitive experiment that involved experimentally manipulating a variable x, a continuous property of a stimulus, looking at the effect on a variable p, the probability of giving a response. The function p(x) was assumed to be a logistic function. The researcher wanted to know how to calculate the point on x at which the fitted logistic regression function equalled 0.5.

### Fitting Nonlinear Regression Models to Multiple Participants Using SPSS

This post briefly discusses how to run a nonlinear regression in SPSS. Specifically, it discusses the scenario where you have a a set of k observations for each of n participants, and where your aim is to fit a nonlinear function to the data of each participant in order to save the parameter estimates for subsequent analysis. This is a relatively common task in psychology. You have multiple participants measured on a numeric repeated measures variable and you want to see how a dependent variable is related to this repeated measures variable. And you want to do this separately for each participant. For example, you might be modelling performance as a function of practice or accuracy as a function of stimulus intensity.

## Sunday, May 16, 2010

### A 34 Minute Video on Using R to Analyse Winter Olympic Medal Data

In this post I present a 34-minute video on using R. The video is based on an analysis of 1924 to 2006 Winter Olympic Medals that I presented previously in text form. The video aims to to show what an interactive session in R might look like using StatET and Eclipse.

## Monday, May 10, 2010

### Abbreviations of R Commands Explained: 250+ R Abbreviations

The R programming language includes many abbreviations. Abbreviations exist in function names, argument names, and allowed values for arguments. This post expands on over 150 R abbreviations with the aim of making it easier for users new to R who are trying to memorise R commands.

## Wednesday, May 5, 2010

### Statistical Power Analysis in G*Power 3

G*Power 3 is an excellent piece of software for performing statistical power analysis. It is particularly useful for applied researchers who need to perform a power analysis as part of their research. The software is free, runs on Windows, and provides a user friendly GUI. G*Power 3 can be downloaded here This post discusses the features of G*Power 3 and provides examples of some of the useful plots that can be generated.

### Videos on Data Analysis with R: Introductory, Intermediate, and Advanced Resources

If you want to learn about R through videos, there are now a large number of options. This post provides links to many of these video under the headings of: (a) What is R? (b) Introductory R, and (c) Intermediate and Advanced R.