Links to specific topics

Wednesday, June 15, 2016

Simpson’s paradox, moderation, and the emergence of quadratic relationships in path models


Among the many innovative features of WarpPLS are those that deal with identification of Simpson’s paradox and modeling of nonlinear relationships. A new article discussing various issues that are important for the understanding of the usefulness of these features is now available. Its reference, abstract, and link to full text are available below.

Kock, N., & Gaskins, L. (2016). Simpson’s paradox, moderation, and the emergence of quadratic relationships in path models: An information systems illustration. International Journal of Applied Nonlinear Science, 2(3), 200-234.

While Simpson’s paradox is well-known to statisticians, it seems to have been largely neglected in many applied fields of research, including the field of information systems. This is problematic because of the strange nature of the phenomenon, the wrong conclusions and decisions to which it may lead, and its likely frequency. We discuss Simpson’s paradox and interpret it from the perspective of path models with or without latent variables. We define it mathematically and argue that it arises from incorrect model specification. We also show how models can be correctly specified so that they are free from Simpson’s paradox. In the process of doing so, we show that Simpson’s paradox may be a marker of two types of co-existing relationships that have been attracting increasing interest from information systems researchers, namely moderation and quadratic relationships.

Among other things this article shows that: (a) Simpson’s paradox may be caused by model misspecification, and thus can in some cases be fixed by proper model specification; (b) a type of model misspecification that may cause Simpson’s paradox involves missing a moderation relationship that exists at the population level; (c) Simpson’s paradox may actually be a marker of nonlinear relationships of the quadratic type, which are induced by moderation; and (d) there is a duality involving moderation and quadratic relationships, which requires separate and targeted analyses for their proper understanding.

Enjoy!

Saturday, June 11, 2016

Interview video: Conference on Information Systems in Latin America


Recently an interview was conducted for the 3rd Conference on Information Systems in Latin America. In it, Dr. Ned Kock was interviewed by Dr. Alexandre Graeml. The topics covered include: structural equation modeling (SEM), partial least squares (PLS) and related techniques, PLS-based SEM, covariance-based SEM, factors versus composites, nonlinear analyses, and WarpPLS.

WarpPLS and its application to research in business and information systems

The link below is for the Conference’s web site.

ISLA 2016 - Information Systems in Latin America Conference

Enjoy!

Thursday, June 9, 2016

PLS-SEM performance with non-normal data


Many claims have been made in the past about the advantages of structural equation modeling employing the partial least squares method (PLS-SEM). While some claims may have been exaggerated, we are continuously finding that others have not. One of such claims, falling in the latter category (i.e., not an exaggeration), is that PLS-SEM is robust to deviations from normality. In other words, PLS-SEM performs quite well with non-normal data.

A new article illustrating this advantage of PLS-SEM is now available. Its reference, abstract, and link to full text are available below.

Kock, N. (2016). Non-normality propagation among latent variables and indicators in PLS-SEM simulations. Journal of Modern Applied Statistical Methods, 15(1), 299-315.

Structural equation modeling employing the partial least squares method (PLS-SEM) has been extensively used in business research. Often the use of this method is justified based on claims about its unique performance with small samples and non-normal data, which call for performance analyses. How normal and non-normal data are created for the performance analyses are examined. A method is proposed for the generation of data for exogenous latent variables and errors directly, from which data for endogenous latent variables and indicators are subsequently obtained based on model parameters. The emphasis is on the issue of non-normality propagation among latent variables and indicators, showing that this propagation can be severely impaired if certain steps are not taken. A key step is inducing non-normality in structural and indicator errors, in addition to exogenous latent variables. Illustrations of the method and its steps are provided through simulations based on a simple model of the effect of e-collaboration technology use on job performance.

The article’s main goal is actually to discuss a method to create non-normal data where the data creator has full access to all data elements, including factor or composite scores and all error terms, and where severe non-normality is extended to error terms. In the process of achieving this goal, the article actually demonstrates that PLS-SEM is very robust to severe deviations from normality, even when these deviations apply to all error terms. This is an issue that is often glossed over in PLS-SEM performance tests with non-normal data.

Readers may also find the YouTube video linked below useful in the context of this discussion.

View Skewness and Kurtosis in WarpPLS

Enjoy!

A thank you note to the participants in the 2016 PLS Applications Symposium


This is just a thank you note to those who participated, either as presenters or members of the audience, in the 2016 PLS Applications Symposium:

http://plsas.net/

As in previous years, it seems that it was a good idea to run the Symposium as part of the Western Hemispheric Trade Conference. This allowed attendees to take advantage of a subsidized registration fee, and also participate in other Conference sessions and the Conference's social event.

I have been told that the proceedings will be available soon from the Western Hemispheric Trade Conference web site.

Also, the full-day workshop on PLS-SEM using the software WarpPLS was well attended. This workshop was fairly hands-on and interactive. Some participants had quite a great deal of expertise in PLS-SEM and WarpPLS. It was a joy to have conducted the workshop!

As soon as we define the dates, we will be announcing next year’s PLS Applications Symposium. Like this years’ Symposium, it will take place in Laredo, Texas, probably in mid-April as well.

Thank you and best regards to all!

Monday, April 18, 2016

Possible installation problems and the MATLAB Compiler Runtime



The vast majority of WarpPLS users do not have any installation problems, but some users do. One possible cause is an incompatibility between the MATLAB Compiler Runtime and their computer's operating system setup. This is explored in more detail below.

Another possible cause of installation problems is one or more software applications that interfere with the proper running of WarpPLS. There have been reports from users suggesting that the following software applications may do that: Panda Antivirus, Norton Antivirus, and XLSTAT.

Yet another possible cause of installation problems are security software tools (to stop malware) that prevent users from making modifications in the folders in their computers that store data about programs. Closely aligned with this cause are security restrictions placed on computers by their organizations' IT offices.

The MATLAB Compiler Runtime

The MATLAB Compiler Runtime is for MATLAB programs what the Java Runtime is for Java programs, and what the Microsoft .NET Framework is for .NET-based programs. That is, it is a set of executable modules that are called by executable files compiled using MATLAB.

WarpPLS is an executable file compiled using MATLAB, and thus requires the MATLAB Compiler Runtime (version 7.14) to run properly. Like many other runtime libraries, the MATLAB Compiler Runtime has originally been developed in C and C++.

MATLAB does not have to be installed for WarpPLS to run

The MATLAB Compiler Runtime is provided in the self-extracting executable file used for the installation of WarpPLS. It is free of charge. MATLAB does not have to be installed for WarpPLS to run, only the specific MATLAB Compiler Runtime that accompanies WarpPLS.

In theory, the MATLAB Compiler Runtime should allow for a “compile once, run everywhere” approach to programming. That is, code that uses the MATLAB Compiler Runtime would be developed on one operating system, compiled, and then deployed, together with the MATLAB Compiler Runtime, to computers running any operating system.

This approach works well in theory, but not always in practice. This comment applies not only to MATLAB but also to Java and .NET applications – you are probably well aware of this if you are a Java or .NET programmer.

Seek professional IT support if you are using an organizational computer

It is possible that a specific user’s computer configuration will prevent the proper installation of the MATLAB Compiler Runtime, by blocking certain operating system configuration changes (e.g., Windows registry changes), as a security measure. This is often the case when organizational computers are used.

Also, a user may not have administrator rights on a computer, or have limited administrator/power user rights, which may prevent certain operating system configuration changes necessary for the proper installation of the MATLAB Compiler Runtime. Having professional IT support in this type of scenario is a must.

Here are a few steps to take if you are having problems installing and running WarpPLS on a Windows computer:

1) Reinstall WarpPLS using the larger file containing the MATLAB Compiler Runtime (approximately 170 MB), choosing the option “Repair”.

There have been reported cases in which users cannot start WarpPLS or move beyond WarpPLS’s first screen. This may happen even if the user has a valid license, with the software behaving as though it is not licensed at all. This may also happen before the user acquires a valid license, while trying to use WarpPLS within the trial license period.

A possible solution here that has worked well in the past is to reinstall WarpPLS using the larger file containing the MATLAB Compiler Runtime. When the MATLAB Compiler Runtime installation software pops up, choose the option “Repair”, and proceed with the full reinstallation.

2) Do the above, but change the folder where the WarpPLS program is installed, choosing a folder that is not in a protected area.

As a possible variation to the above, you may change the folder where the WarpPLS program is installed, choosing a folder that is not in a protected area. For example, you may choose the folder “C:\WarpPLS” or the folder “C:\WarpPLS [version; e.g., 5.0]”. Being outside a protected area prevents certain software, such as antivirus software and malware, from interfering with WarpPLS’s execution.

3) Completely uninstall the MATLAB Compiler Runtime and WarpPLS, disable any antivirus software currently running, reinstall the MATLAB Compiler Runtime and WarpPLS, and then re-enable the antivirus software.

To uninstall the MATLAB Compiler Runtime, follow the following procedure (or a similar procedure, depending on the version of Windows you are using): go the “Control Panel”, click on “Add or Remove Programs” or “Programs and Features”, and uninstall the MATLAB Compiler Runtime.

To uninstall the main software program (i.e., WarpPLS), simply delete the main software installation folder. This folder is usually “C:\Program Files\WarpPLS [version; e.g., 5.0]” or “C:\Program Files (x86)\WarpPLS [version]”, unless you chose a different folder for the main software program during the installation process. Then delete the shortcut created by the software from the desktop.

4) Check the "Program Files" and the "Program Files (x86)" directories (assuming that the MATLAB Compiler Runtime is installed on the C drive), to see if one of the following folders is there.

C:\Program Files\MATLAB\MATLAB Compiler Runtime\v714\runtime\win32

C:\Program Files (x86)\MATLAB\MATLAB Compiler Runtime\v714\runtime\win32

If not, make sure that you are logged into your computer with full administrator rights, and reinstall the MATLAB Compiler Runtime. You can do that running the self-installing .exe file (approximately 170 MB) for WarpPLS, which includes the MATLAB Compiler Runtime. Or, contact your local IT support, and ask them to help you do so.

5) Go to the Command Prompt and type “PATH”, to see if one of the following paths shows on the list provided.

C:\Program Files\MATLAB\MATLAB Compiler Runtime\v714\runtime\win32

C:\Program Files (x86)\MATLAB\MATLAB Compiler Runtime\v714\runtime\win32

If not, on the Command Prompt, type one of the following commands, depending on the folder in which the MATLAB Compiler Runtime is installed:

set PATH=C:\Program Files\MATLAB\MATLAB Compiler Runtime\v714\runtime\win32;%PATH%

set PATH=C:\Program Files (x86)\MATLAB\MATLAB Compiler Runtime\v714\runtime\win32;%PATH%

Then type “PATH” again, and make sure that the new path has been added. This will change the Windows registry; a minor and pretty harmless change. If you are concerned about making registry changes yourself, or cannot do that due to limited rights or any other reason, please contact your local IT support, and ask them to help you do so.

6) Try to install WarpPLS on a different computer, and see if it runs well there.

This last step is annoying but important because there are certain computer-specific configuration setups, or even malware allowed in by those setups, that may prevent the MATLAB Compiler Runtime from properly installing or executing. This is rare, but does happen sometimes. Comparing computers can help solve problems like these.

If you can install and run WarpPLS on one computer, but not on another, there may be a computer configuration or malware problem that is preventing you from doing so. If you have access to good-quality local IT support, you should contact it, and ask them to help you identify and solve the problem.

Saturday, April 16, 2016

PLS Applications Symposium; 13 - 15 April 2016; Laredo, Texas


PLS Applications Symposium; 13 - 15 April 2016; Laredo, Texas
(Abstract submissions accepted until 4 March 2016)

*** Only abstracts are needed for the submissions ***

The partial least squares (PLS) method has increasingly been used in a variety of fields of research and practice, particularly in the context of PLS-based structural equation modeling (SEM). The focus of this Symposium is on the application of PLS-based methods, from a multidisciplinary perspective. For types of submissions, deadlines, and other details, please visit the Symposium’s web site:

http://plsas.net

*** Workshop on PLS-SEM ***

On 13 April 2015 a full-day workshop on PLS-SEM will be conducted by Dr. Ned Kock, using the software WarpPLS. This workshop will be hands-on and interactive. To participate in the workshop, please indicate your interest when making your registration for the Symposium.

The following topics, among others, will be covered - Running a Full PLS-SEM Analysis - Conducting a Moderating Effects Analysis - Viewing Moderating Effects via 3D and 2D Graphs - Creating and Using Second Order Latent Variables - Viewing Indirect and Total Effects - Viewing Skewness and Kurtosis of Manifest and Latent Variables - Conducting a Multi-group Analysis with Range Restriction - Viewing Nonlinear Relationships - Conducting a Factor-Based PLS-SEM Analysis - Viewing and Changing Missing Data Imputation Settings - Isolating Mediating Effects - Identifying and Dealing with Outliers - Solving Indicator Problems - Solving Collinearity Problems.

-----------------------------------------------------------
Ned Kock
Symposium Chair
http://plsas.net


Monday, February 8, 2016

Conducting a nonlinear robust path analysis


What if a researcher has only one measure for each latent variable, and still wants to perform a nonlinear “robust” analysis where no parametric assumptions (e.g., univariate or multivariate normality) are made beforehand?

This would call for a new nonlinear robust multivariate analysis approach – a nonlinear robust path analysis. Through this approach the variables in the structural model would not be “latent”, strictly speaking, and thus other assessments would have to be performed in place of a confirmatory factor analysis. That is, without multiple indicators per latent variable measurement, quality assessments must deviate somewhat from what would be used in a traditional structural equation modeling analysis.

A new article illustrating a nonlinear robust path analysis with WarpPLS is now available. To the best of our knowledge, this is one of the first published articles employing this type of analysis. The full reference, link to full text PDF file maintained by the University of California, and abstract for the article are available below.

Kock, N. (2015). Wheat flour versus rice consumption and vascular diseases: Evidence from the China Study II data. Cliodynamics, 6(2), 130–146.

PDF file:

http://escholarship.org/uc/item/7hk1254d

Why does wheat flour consumption appear to be significantly associated with vascular diseases? To answer this question we analyzed data on rice consumption, wheat flour consumption, total calorie consumption, and mortality from vascular diseases obtained from the China Study II dataset. This dataset covers the years of 1983, 1989 and 1993; with data related to biochemistry, diet, lifestyle, and mortality from various diseases in 69 counties in China. Our analyses point at a counterintuitive conclusion: it may not be wheat flour consumption that is the problem, but the culture associated with it, characterized by: decreased levels of physical activity, decreased exposure to sunlight, increased consumption of processed foods, and increased social isolation. Wheat flour consumption may act as a proxy for the extent to which this culture is expressed in a population. The more this culture is expressed, the greater is the prevalence of vascular diseases.

While this is an academic article, I think that the main body of the article is fairly easy to read; which was one of the expectations communicated to us by the Editor and the reviewers. WarpPLS users may find themselves in this same situation – having to prevent more technical statistical material from “spoiling” the reading experience of a non-technical audience. In this case, more technical readers may want to check under “Supporting material”, which is one of the links on the left, where they will find a detailed description of the data used and the results of some specialized statistical tests.

Enjoy!