News and Updates

Categories

The Cronbach’s Alphas for all the scales in my path analysis are in the .7s, so why is a reviewer criticizing me for not paying sufficient attention to reliability?

December 21, 2019

The issue of reliability can be a complex and often misunderstood issue. Entire text books have been written about reliability, validity, and scale construction, so we only briefly touch on the key issues here (see Bandalos, 2018, for an excellent recent example). To begin, in most areas across the behavioral, educational, and health sciences, theoretical constructs are hypothesized to exist yet cannot be directly measured. Common examples include depression, anxiety, academic motivation, commitment to treatment, and perceived stress. A vast array of psychometric methods have been developed over the past century to use multi-item scales as a basis to infer the existence of these underlying constructs. Indeed, the genesis of factor analysis (most commonly dated to Spearman in 1903) was motivated by the desire to use multi-test assessments to compute person-specific values of cognitive functioning. Psychometric methods are sometimes organized into pragmatic approaches (e.g., Classical Test Theory) and axiomatic approaches (e.g., item response theory and factor analysis). However, a fundamental component of all of these methods is reliability.

(more…)

Read More

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

Read More

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.

Read More

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.

(more…)

Read More

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.

(more…)

Read More