inst/shiny-apps/mod2/aboutdata.md

In bcdudek/bcdstats: A collection of functions to support B. Dudek's APSY510/511 classes

Regression Models with a Numeric DV and two IV's, either Categorical or Numeric

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Two Categorical IVs:

======================================================== Data were simulated for these illustrations.

The two categorical IVs are both illustrated as having two levels. This makes the illustration a traditional 2x2 ANOVA design. Bar graph depictions with Simple Main Effects illustrated, reinforce this traditional anaylysis perspective.

In each case, sample size per group was esatablished as n=4, and the data were systematically created to produce numerical differences in cell means that are visually simple.

The Regression approach to data analysis of 2x2 designs switches to depiction of the data in a 3D Scatterplot, with regression surfaces included. Visualizing Simple Main Effects on these surfaces is a key goal of this app.

Two 2x2 ANOVA data sets were created for these Two-categorical IV's illustrations:

======================================================== One had no interaction and therefore an additive regression model is appropriate (fit the two-IV, main effects only, regression plane). The other had an interaction (therrefore, Simple Main Effects differ), and the warped regression surface is depicted. In this latter interaction model, the regression equation had the two main effect coding vectors plus their product term for the interaction.

In depictions of both data sets, the IV's are seen (in the 3D plots), to have been contrast coding vectors (+1, and -1 coefficients for the two levels) for the main effects.

One Categorical IV, one Quantitative IV

======================================================== Systolic blood pressure was predicted, in a linear regression model, from smoker status and body weight. These data were taken from the publicly available NHANES data set (https://www.cdc.gov/nchs/nhanes/index.htm)

In order to facilitate the visualizations, a random subsample of the full data set was taken. The outcome of the study in this subset of data may not be identical to the analsyses on the full data set. Therefore, the presentation of the data here should be viewed only in an instructional context for visualizing interaction and simple slopes. Users are advised to NOT draw scientific conclusions from these depictions.

Two Quantitative IVs

======================================================== The data set used in this set of visualizations has been provided by Professor James Boswell, and is from a psychological treatment study. Baseline indices of Depression severity, Anxiety Severity, and Positive Affect were acquired on a sample of clients prior to treatment. These simple measurements permit investigation of the relative and interactive importance of Anxiety and Positivity in their relationship to Depression scores. It is not surprising that Anxiety Scores and Depression scores are positively related.

The interesting question is whether Postitive Affect moderates this relationship. The analysis presented in these visualizations is superficial and is only intended for instructional purposes in seeing interaction and Simple Slopes. Any strong scientific conclusions based on these depictions would be premature.

bcdudek/bcdstats documentation built on Jan. 3, 2024, 10:09 p.m.