Corrigendum: Repeated Measures Correlation

Bakdash, Jonathan Z.; Marusich, Laura R.

doi:10.3389/fpsyg.2019.01201

CORRECTION article

Front. Psychol., 28 May 2019

Sec. Quantitative Psychology and Measurement

Volume 10 - 2019 | https://doi.org/10.3389/fpsyg.2019.01201

Corrigendum: Repeated Measures Correlation

This article is a correction to:

Repeated Measures Correlation
1. Read original article

$\nJonathan Z. Bakdash$ Jonathan Z. Bakdash¹^*

Laura R. Marusich²

¹US Army Research Laboratory, Human Research and Engineering Directorate, Aberdeen Proving Ground, United States
²US Army Laboratory South Field Element, Human Research and Engineering Directorate, University of Texas Arlington, Arlington, TX, United States

A Corrigendum on
Repeated Measures Correlation

by Bakdash, J. Z., and Marusich, L. R. (2017). Front. Psychol. 8:456. doi: 10.3389/fpsyg.2017.00456

In the original article, there were errors in Equations 2 and 3¹. For Equations 2 and 3, j should be the participant and i the trial/repeated measure (i and j are swapped for consistency with Equation 1). In Equation 2, ${\bar{M e a s u r e 2}}_{i}$ should be ${\bar{M e a s u r e 1}}_{j}$ . Additionally, the notation using c is confusing in Equation 2 and incorrect in Equation 3. Last, the left side of Equation 3 is incorrect, it should be the predicted value not its mean.

Corrections have been made to the Background section, subsection Rmcorr and ANCOVA, Equations and rmcorr Table, paragraphs four and five:

In Equations 2 and 3, Equation 1 is rewritten for rmcorr to show one measure as a function of its mean value, participant, and the covaried value of the other measure. Note following Equation 1, i and j are now exchanged for consistency: j = participant and i = trial or repeated measure.

\begin{array}{l} {M e a s u r e 1}_{i j} = {\bar{M e a s u r e 1}}_{j} + P a r t i c i p a n t_{j} + β ({M e a s u r e 2}_{i j} - {\bar{M e a s u r e 2}}_{j}) + ε_{i j} & (2) \end{array}

Measure1 and Measure2 are exchangeable.

Measure1_ij is the value of Measure1 for the jth participant at their ith trial.

${\bar{M e a s u r e 1}}_{j}$ is the mean of Measure1 (all i trials) for the jth participant.

Participant_j is a unique identifier that acts as a dummy or proxy coded variable.

β is the value of the covariate, which is the overall or common slope.

Measure2_ij is the value of Measure2 for the jth participant at their ith trial.

${\bar{M e a s u r e 2}}_{j}$ is the mean of Measure2 (all i trials) for the jth participant.

ε_ij is the error for the jth participant at their ith trial.

Equation 2 is rewritten to calculate the predicted value of the rmcorr regression line for each participant by trial. We drop the error term because we do not fit a confidence interval for the regression line.

\begin{array}{l} {M e a s u r e 1}_{i j}^{'} = {\bar{M e a s u r e 1}}_{j} + P a r t i c i p a n t_{j} + β ({M e a s u r e 2}_{i j} - {\bar{M e a s u r e 2}}_{j}) & (3) \end{array}

$M e a s u r e 1_{i j}^{'}$ is the predicted y-value of Measure1 for the jth participant at their ith trial.

Measure2_ij is the actual x-value which corresponds to the predicted y-value in the regression line.

Please note that the rmcorr package has always produced the corrected results.

The authors apologize for these errors and state that they do not change the scientific conclusions of the article in any way. The original article has been updated.

Footnotes

1. ^We are grateful to Alexander Wedel for identifying these errors and also thank him for helping correct the equations.

Keywords: correlation, repeated measures, individual differences, intra-individual, statistical power, multilevel modeling

Citation: Bakdash JZ and Marusich LR (2019) Corrigendum: Repeated Measures Correlation. Front. Psychol. 10:1201. doi: 10.3389/fpsyg.2019.01201

Received: 15 April 2019; Accepted: 07 May 2019;
Published: 28 May 2019.

Edited and reviewed by: Prathiba Natesan, University of North Texas, United States

Copyright © 2019 Bakdash and Marusich. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Jonathan Z. Bakdash, jonathan.z.bakdash.civ@mail.mil

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