Posts

New tutorial paper on BC-SMD effect sizes

I’m pleased to announce that the Campbell Collaboration has just published a new discussion paper that I wrote with my colleagues Jeff Valentine and Emily Tanner-Smith about between-case standardized mean difference effect sizes for single-case designs.
2016-12-19

Presentation at IES 2016 PI meeting

I am just back from the Institute of Education Sciences 2016 Principal Investigators meeting. Rob Horner had organized a session titled “Single-case methods: Current status and needed directions” as a tribute to our colleague Will Shadish, who passed away this past year.
2016-12-19

Bug in nlme::lme with fixed sigma and REML estimation

About one year ago, the nlme package introduced a feature that allowed the user to specify a fixed value for the residual variance in linear mixed effect models fitted with lme().
2016-11-07

What is Tau-U?

Parker, Vannest, Davis, and Sauber (2011) proposed the Tau-U index—actually several indices, rather—as effect size measures for single-case designs. The original paper describes several different indices that involve corrections for trend during the baseline phase, treatment phase, both phases, or neither phase.
2016-11-03

New working paper: Procedural sensitivities of SCD effect sizes

I’ve just posted a new version of my working paper, Procedural sensitivities of effect sizes for single-case designs with behavioral outcome measures. The abstract is below. This version is a major update of an earlier paper that focused only on the non-overlap measures.
2016-10-17

Simulation studies in R (Fall, 2016 version)

In today’s Quant Methods colloquium, I gave an introduction to the logic and purposes of Monte Carlo simulation studies, with examples written in R. Here are the slides from my presentation.
2016-09-28

Bug in nlme::getVarCov

I have recently been working to ensure that my clubSandwich package works correctly on fitted lme and gls models from the nlme package, which is one of the main R packages for fitting hierarchical linear models.
2016-08-10

Alternative formulas for the standardized mean difference

The standardized mean difference (SMD) is surely one of the best known and most widely used effect size metrics used in meta-analysis. In generic terms, the SMD parameter is defined as the difference in population means between two groups (often this difference represents the effect of some intervention), scaled by the population standard deviation of the outcome metric.
2016-06-03

Assigning after dplyr

Hadley Wickham’s dplyr and tidyr packages completely changed the way I do data manipulation/munging in R. These packages make it possible to write shorter, faster, more legible, easier-to-intepret code to accomplish the sorts of manipulations that you have to do with practically any real-world data analysis.
2016-05-13

Unlucky randomization

A colleague asked me the other day: I wonder if you have any suggestions for what to do if random assignment results in big group differences on the pre-test scores of the main outcome measure?
2016-05-11