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A New Podcast on All Things Quantitative: Quantitude

October 30, 2019

Our very own Patrick Curran has teamed up with Greg Hancock (Professor, College of Education, University of Maryland) to launch a new podcast called Quantitude. It is dedicated to all things quantitative, ranging from the relevant to the highly irrelevant. Picture a cross between the Car Talk guys, the two old men from the Muppets, and a graduate statistics course.

Quantitude explores serious issues but in a sometimes grousing and irreverent way. Episodes address current topics in quantitative methodology, data analysis, and research methods; interviews with professionals in the field; responses to listener questions; quantitative puzzlers; and much more. Episodes are posted every-other week, notably on “Quanti-Tudesday”.

So if you’re interested, please check Quantitude out. The podcast can be found at https://www.buzzsprout.com/639103 (or wherever you listen to your favorite podcasts), and the Quantitude home page is http://quantitudethepodcast.org/. Finally, Quantitude is on Twitter at @quantitudepod

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2020 Summer Workshops

October 2, 2019

We’re pleased to announce our summer workshop schedule for 2020. The schedule for our regular 5-Day workshops is:

In addition, we are pleased to again offer a steeply reduced cost ($100) 3-day introductory workshop designed specifically for graduate students seeking advanced methodological training:

Given high demand, students are asked to pre-register for this event by March 20, 2020, and will be notified if they have been selected to attend by April 1, 2020.

See our Training page for a general description of our teaching philosophy, links to course reviews and sample course notes.

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How can I estimate statistical power for a structural equation model?

July 6, 2019

This is a question that often arises when using structural equation models in practice, sometimes once a study is completed but more often in the planning phase of a future study. To think about power, we must first consider ways in which we can make errors in hypothesis testing (Cohen, 1992). Briefly, the Type I error rate is the probability of incorrectly rejecting a true null hypothesis; this is the probability that an effect will be found in a sample when there is truly no effect in the population. In contrast, the Type II error rate is the probability of accepting a false null hypothesis; this is the probability that an effect will not be found in a sample when there truly is an effect in the population. Statistical power is one minus the Type II error rate and represents the probability of correctly rejecting a false null hypothesis; this is the probability that an effect will be found in the sample if an effect truly exists in the population. It is important to determine whether a proposed study will have sufficient power to detect an effect if an effect really exists. Although power is quite easy to compute for simple kinds of tests such as a t-test or for a regression parameter, it becomes increasingly complicated to compute power for complex SEMs.

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What are modification indices and should I use them when fitting SEMs to my own data?

June 10, 2019

This is a great question and is one that prompts much disagreement among quantitative methodologists. Nearly all confirmatory factor analysis or structural equation models impose some kind of restrictions on the number parameters to be estimated. Usually, some parameters are set to zero (and thus not estimated at all), but sometimes restrictions come in the form of equality constraints or other kinds of structured relations among parameters. The model chi-square test reflects the extent to which these imposed restrictions impede the ability of the model to reproduce the means, variances, and covariances that were observed in the sample. Smaller chi-square values reflect that the estimated model is able to adequately reproduce the observed sample statistics whereas larger values reflect that some aspect of the hypothesized model is inconsistent with characteristics of the observed sample.

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Do you have any materials that demonstrate how to estimate structural equation models using lavaan in R?

April 24, 2019

This is a question we often hear, particularly from students and junior researchers who don’t have access to sometimes expensive commercial software for fitting structural equation models. It is possible to estimate a wide array of SEMs, ranging from simple path models to fully latent SEMs to growth curve models and beyond, using the lavaan package within R. For those who may be interested, we have developed detailed demonstrations of how to estimate a broad class of SEMs using lavaan and these are now freely available for download.

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