Objective

According to Wikipedia, stepwise regression is a method of fitting regression models whereby an automatic procedure chooses the predictive variables. The procedure is a step-by-step iterative process that considers a variable for addition to or subtraction from the set of explanatory variables based on a pre-specified criterion. Usually, stepwise regression takes the form of forward selection, backward elimination, or bidirectional elimination.

The vignette conducts a stepwise regression on a dataset of 218 respondents experiencing significant organisational change. Respondents reported their self-efficacy, irrational ideas, maladaptive defence mechanisms, emotion, behavioural intentions and reaction towards change in their organisation.

This vignette compares and evaluates the goodness of fit for each model derived from the stepwise regression.

Workflow

The raw data set was wrangled and tidied before processing. Conducted a brief exploratory analysis comprising a statistical summary and correlation analysis to understand the variables.

Proceeded to implement forward selection, backward elimination and bidirectional elimination, which resulted in two final models. The preferred model was selected for further investigation. This included:

  • a review of model assumptions
  • model correlation and network analysis
  • visualising the relationship between the most significant explanatory variables and the response variable
  • visualising the relationship between the most significant explanatory variable and the response variable segmented by categorical variables.

Results

1. Explore variables

The data set was filtered to those respondents who reported experiencing significant organisational change. Table 1 is a statistical summary of the proposed explanatory variables and the response variable (reaction).

Table 1 Statistical summary of explanatory and response variables
vars n mean sd median trimmed mad min max range skew kurtosis se
self_efficacy 1 218 5.56 0.80 5.65 5.64 0.76 1.71 6.94 5.24 -1.21 2.80 0.05
needs_approval 2 218 4.20 1.39 4.00 4.23 1.48 1.00 7.00 6.00 -0.14 -0.70 0.09
fears_failure 3 218 4.08 1.51 4.00 4.09 1.48 1.00 7.00 6.00 -0.01 -0.85 0.10
labelling_blame 4 218 3.19 1.32 3.00 3.11 1.48 1.00 7.00 6.00 0.54 -0.32 0.09
catastrophising 5 218 3.73 1.32 3.50 3.69 1.48 1.00 7.00 6.00 0.14 -0.89 0.09
managing_feelings 6 218 3.91 1.30 4.00 3.91 1.48 1.00 6.50 5.50 -0.08 -0.68 0.09
anxious_thoughts 7 218 4.12 1.16 4.00 4.15 0.74 1.50 7.00 5.50 -0.18 -0.39 0.08
avoidance 8 218 2.25 0.98 2.00 2.14 0.74 1.00 5.50 4.50 1.04 0.91 0.07
past_influences 9 218 2.79 1.31 2.50 2.71 1.48 1.00 6.00 5.00 0.58 -0.72 0.09
facing_reality 10 218 4.56 1.43 5.00 4.62 1.48 1.00 7.00 6.00 -0.34 -0.78 0.10
passive_existence 11 218 4.23 1.23 4.00 4.26 1.48 1.00 7.00 6.00 -0.15 -0.47 0.08
dissociation 12 218 2.73 1.20 2.50 2.61 0.74 1.00 6.50 5.50 0.89 0.27 0.08
displacement 13 218 3.06 1.28 3.00 3.01 1.48 1.00 7.00 6.00 0.34 -0.52 0.09
isolation_of_affect 14 218 3.40 1.50 3.50 3.37 2.22 1.00 7.00 6.00 0.16 -0.94 0.10
reaction_formation 15 218 4.14 1.23 4.00 4.14 1.48 1.50 7.00 5.50 0.11 -0.59 0.08
denial 16 218 2.51 1.04 2.00 2.44 0.74 1.00 6.50 5.50 0.77 0.30 0.07
projection 17 218 2.50 1.11 2.00 2.40 0.74 1.00 6.00 5.00 0.86 0.07 0.07
passive_aggression 18 218 2.59 1.06 2.50 2.49 0.74 1.00 6.50 5.50 0.92 0.67 0.07
acting_out 19 218 3.56 1.34 3.50 3.55 1.48 1.00 6.50 5.50 0.04 -0.87 0.09
emotion 20 218 3.80 1.13 3.80 3.79 1.11 1.00 6.90 5.90 0.09 -0.22 0.08
behavioural_intentions 21 218 5.08 1.11 5.25 5.15 1.19 1.75 7.00 5.25 -0.58 -0.17 0.08
reaction 22 218 4.23 1.91 5.00 4.31 1.48 1.00 7.00 6.00 -0.27 -1.37 0.13

Chart 1 supports Table 1, showing correlation coefficients between each variable.

2. Stepwise regression

Prepared and implemented three methods of stepwise regression (forward selection, backward elimination and bidirectional elimination). The three methods produced two different but similar models. Reviewed the parameters for both models and compared model fit.

2.1 Model 1

Table 2 summarises the parameters for Model 1, derived from forward selection. The number of explanatory variables reduced from 21 in Table 1 to seven, shown in Table 2. Table 2 p-values show that the explanatory variables isolation of affect, avoidance, emotion and behavioural intentions are statistically significant. The coefficient of determination is also significant, with an adjusted R2 of 0.718.

Table 2 Parameters for Model 1
Parameter Coefficient SE 95% CI t(210) p
(Intercept) -3.82 0.51 (-4.82, -2.82) -7.53 < .001
behavioural intentions 1.05 0.09 (0.87, 1.23) 11.66 < .001
emotion 0.57 0.09 (0.39, 0.74) 6.41 < .001
avoidance 0.26 0.08 (0.10, 0.42) 3.14 0.002
isolation of affect 0.11 0.05 (0.01, 0.21) 2.20 0.029
denial -0.15 0.08 (-0.30, 1.55e-03) -1.95 0.052
fears failure 0.08 0.05 (-8.75e-03, 0.17) 1.78 0.076
reaction formation -0.09 0.06 (-0.20, 0.02) -1.56 0.120
Model: reaction ~ behavioural_intentions + emotion + avoidance + isolation_of_affect + denial + fears_failure + reaction_formation (218 Observations)
Residual standard deviation: 1.014 (df = 210)
R2: 0.727; adjusted R2: 0.718

Chart 2 plots important explanatory variables for Model 1.

The equation derived for Model 1 follows.

\[ \small \begin{aligned} \operatorname{\widehat{reaction}} &= -3.82 + 1.05(\operatorname{behavioural\_intentions})\ + \\ &\quad 0.57(\operatorname{emotion}) + 0.26(\operatorname{avoidance})\ + \\ &\quad 0.11(\operatorname{isolation\_of\_affect}) - 0.15(\operatorname{denial})\ + \\ &\quad 0.08(\operatorname{fears\_failure}) - 0.09(\operatorname{reaction\_formation}) \end{aligned} \]

2.2 Model 2

Table 3 summarises the parameters for Model 2, derived from backward elimination and bidirectional elimination. The number of explanatory variables reduced from 21 in Table 1 to 11 in Table 3. Table 3 p-values show that the explanatory variables reaction formation, anxious thoughts, isolation of affect, avoidance, emotion and behavioural intentions are statistically significant. The coefficient of determination is also significant, with an adjusted R2 of 0.725.

Table 3 Parameters for Model 2
Parameter Coefficient SE 95% CI t(206) p
(Intercept) -3.85 0.62 (-5.08, -2.63) -6.23 < .001
fears failure 0.08 0.05 (-0.02, 0.17) 1.50 0.134
catastrophising -0.10 0.07 (-0.23, 0.03) -1.47 0.142
managing feelings 0.12 0.07 (-0.02, 0.26) 1.71 0.089
anxious thoughts 0.14 0.07 (1.95e-03, 0.27) 2.00 0.047
avoidance 0.23 0.09 (0.06, 0.39) 2.65 0.009
facing reality -0.10 0.06 (-0.22, 0.02) -1.69 0.092
isolation of affect 0.11 0.05 (0.02, 0.21) 2.28 0.023
reaction formation -0.11 0.06 (-0.23, -7.19e-04) -1.98 0.049
denial -0.12 0.08 (-0.28, 0.03) -1.57 0.118
emotion 0.58 0.10 (0.39, 0.77) 6.10 < .001
behavioural intentions 1.04 0.09 (0.86, 1.21) 11.50 < .001
Model: reaction ~ fears_failure + catastrophising + managing_feelings + anxious_thoughts + avoidance + facing_reality + isolation_of_affect + reaction_formation + denial + emotion + behavioural_intentions (218 Observations)
Residual standard deviation: 1.002 (df = 206)
R2: 0.739; adjusted R2: 0.725

Chart 3 plots important explanatory variables for Model 2.

The equation derived for Model 2 follows.

\[ \small \begin{aligned} \operatorname{\widehat{reaction}} &= -3.85 + 0.08(\operatorname{fears\_failure})\ - \\ &\quad 0.1(\operatorname{catastrophising}) + 0.12(\operatorname{managing\_feelings})\ + \\ &\quad 0.14(\operatorname{anxious\_thoughts}) + 0.23(\operatorname{avoidance})\ - \\ &\quad 0.1(\operatorname{facing\_reality}) + 0.11(\operatorname{isolation\_of\_affect})\ - \\ &\quad 0.11(\operatorname{reaction\_formation}) - 0.12(\operatorname{denial})\ + \\ &\quad 0.58(\operatorname{emotion}) + 1.04(\operatorname{behavioural\_intentions}) \end{aligned} \]

3. Compare models

Table 4 compares the results of both models side-by-side.

Table 4 Compare output for Models 1 and 2
  Model 1 (Response: reaction) Model 2 (Response: reaction)
Predictors Estimates std. Beta CI standardized CI p Estimates std. Beta CI standardized CI p
(Intercept) -3.82 *** 0.00 -4.82 – -2.82 -0.07 – 0.07 <0.001 -3.85 *** 0.00 -5.08 – -2.63 -0.07 – 0.07 <0.001
behavioural intentions 1.05 *** 0.61 0.87 – 1.23 0.51 – 0.72 <0.001 1.04 *** 0.60 0.86 – 1.21 0.50 – 0.71 <0.001
emotion 0.57 *** 0.33 0.39 – 0.74 0.23 – 0.44 <0.001 0.58 *** 0.34 0.39 – 0.77 0.23 – 0.45 <0.001
avoidance 0.26 ** 0.13 0.10 – 0.42 0.05 – 0.22 0.002 0.23 ** 0.12 0.06 – 0.39 0.03 – 0.20 0.009
isolation of affect 0.11 * 0.09 0.01 – 0.21 0.01 – 0.16 0.029 0.11 * 0.09 0.02 – 0.21 0.01 – 0.17 0.023
denial -0.15 -0.08 -0.30 – 0.00 -0.17 – 0.00 0.052 -0.12 -0.07 -0.28 – 0.03 -0.15 – 0.02 0.118
fears failure 0.08 0.07 -0.01 – 0.17 -0.01 – 0.14 0.076 0.08 0.06 -0.02 – 0.17 -0.02 – 0.14 0.134
reaction formation -0.09 -0.06 -0.20 – 0.02 -0.13 – 0.01 0.120 -0.11 * -0.07 -0.23 – -0.00 -0.15 – -0.00 0.049
catastrophising -0.10 -0.07 -0.23 – 0.03 -0.16 – 0.02 0.142
managing feelings 0.12 0.08 -0.02 – 0.26 -0.01 – 0.18 0.089
anxious thoughts 0.14 * 0.08 0.00 – 0.27 0.00 – 0.16 0.047
facing reality -0.10 -0.08 -0.22 – 0.02 -0.16 – 0.01 0.092
Observations 218 218
R2 / R2 adjusted 0.727 / 0.718 0.739 / 0.725
AIC 634.648 633.144
  • p<0.05   ** p<0.01   *** p<0.001

Output 1 compares the fit statistics for Models 1 and 2. Both models produced very similar results. Therefore, either model could be selected depending on requirements. It could be argued that Model 1 is preferred because it achieves this close result with fewer explanatory variables and has the lower BIC. It could be argued Model 2 is preferred because it has a lower AIC and higher adjusted R2.

Output 1 Model fit statistics

$Models
  Formula                                                                                                                                                                                                
1 "reaction ~ behavioural_intentions + emotion + avoidance + isolation_of_affect + denial + fears_failure + reaction_formation"                                                                          
2 "reaction ~ fears_failure + catastrophising + managing_feelings + anxious_thoughts + avoidance + facing_reality + isolation_of_affect + reaction_formation + denial + emotion + behavioural_intentions"

$Fit.criteria
  Rank Df.res   AIC  AICc   BIC R.squared Adj.R.sq   p.value Shapiro.W
1    8    210 634.6 635.5 665.1    0.7270   0.7179 1.028e-55    0.9925
2   12    206 633.1 634.9 677.1    0.7386   0.7246 6.128e-54    0.9947
  Shapiro.p
1    0.3354
2    0.6461

Another test for comparing regression models is the analysis of variance (ANOVA). ANOVA determines which model has the best parsimonious fit. Output 2 is an ANOVA comparison of both models. With four additional explanatory variables, the p-value for Model 2 is not less than 0.05. Therefore it is inferred that Model 1, derived from forward selection, has a better fit for this data set.

Output 2 ANOVA model comparison

Analysis of Variance Table

Model 1: reaction ~ behavioural_intentions + emotion + avoidance + isolation_of_affect + 
    denial + fears_failure + reaction_formation
Model 2: reaction ~ fears_failure + catastrophising + managing_feelings + 
    anxious_thoughts + avoidance + facing_reality + isolation_of_affect + 
    reaction_formation + denial + emotion + behavioural_intentions
  Res.Df    RSS Df Sum of Sq      F Pr(>F)  
1    210 216.00                             
2    206 206.79  4    9.2144 2.2948 0.0605 .
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

4. Supplementary analysis

Model 1 was assessed as the preferred model. The remainder of this vignette provides supplementary analysis.

4.1 Model assumptions

Chart 4 checks assumptions for Model 1. This includes the model’s linearity, homogeneity, outliers, multicollinearity and residuals. Despite variable labels overlapping in the collinearity chart, collinearity levels are low in this model.

Chart 4 Model 1 assumptions

4.2 Model correlations

Chart 5 summarises the correlation coefficients for Model 1.

Chart 6 visualises correlated relationships between the variables. Highly correlated variables, either positively or negatively, appear closer together and are joined by a stronger path.

4.3. Visualise relationships

Chart 7 visualises the relationship between the two most significant explanatory variables and the response variable.

4.4. Visualise relationship with categorical variables

Finally, Chart 8 visualises the relationship between behavioural intentions and reaction segmented by categorical variables.


References:

Self-efficacy was measured using the ‘Self-efficacy scale: Construction and validation’ by Sherer, Maddux, Mercandante, Prentice-Dunn and Rogers, published in Psychological Reports.
Irrational ideas were measured using the ‘Irrational belief scale’ developed by Malouff and Schutte, published in the Sourcebook of Adult Assessment Strategies, based on Ellis and Harper’s work, published in A New Guide to Rational Living.
Maladaptive defence mechanisms were measured using selected items from ‘The Defense Style Questionnaire’ by Andrews, Singh and Bond, published in The Journal of Nervous and Mental Disease.
Emotion was measured using ‘A semantic differential mood scale’ by Lorr and Wunderlich, published in the Journal of Clinical Psychology.


Session information and package update

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##  rprojroot      2.0.4    2023-11-05 [1] CRAN (R 4.4.0)
##  rstatix        0.7.2    2023-02-01 [1] CRAN (R 4.4.0)
##  rstudioapi     0.16.0   2024-03-24 [1] CRAN (R 4.4.0)
##  sandwich       3.1-0    2023-12-11 [1] CRAN (R 4.4.0)
##  sass           0.4.9    2024-03-15 [1] CRAN (R 4.4.0)
##  scales         1.3.0    2023-11-28 [1] CRAN (R 4.4.0)
##  see          * 0.8.5    2024-07-17 [1] CRAN (R 4.4.1)
##  sessioninfo    1.2.2    2021-12-06 [1] CRAN (R 4.4.0)
##  shiny          1.8.1.1  2024-04-02 [1] CRAN (R 4.4.0)
##  sjlabelled     1.2.0    2022-04-10 [1] CRAN (R 4.4.0)
##  sjmisc         2.8.10   2024-05-13 [1] CRAN (R 4.4.0)
##  sjPlot       * 2.8.16   2024-05-13 [1] CRAN (R 4.4.0)
##  sjstats        0.19.0   2024-05-14 [1] CRAN (R 4.4.0)
##  stringi        1.8.4    2024-05-06 [1] CRAN (R 4.4.0)
##  stringr      * 1.5.1    2023-11-14 [1] CRAN (R 4.4.0)
##  survival       3.5-8    2024-02-14 [2] CRAN (R 4.4.0)
##  svglite        2.1.3    2023-12-08 [1] CRAN (R 4.4.0)
##  systemfonts    1.1.0    2024-05-15 [1] CRAN (R 4.4.0)
##  TH.data        1.1-2    2023-04-17 [1] CRAN (R 4.4.0)
##  tibble       * 3.2.1    2023-03-20 [1] CRAN (R 4.4.0)
##  tidyr        * 1.3.1    2024-01-24 [1] CRAN (R 4.4.0)
##  tidyselect     1.2.1    2024-03-11 [1] CRAN (R 4.4.0)
##  tidyverse    * 2.0.0    2023-02-22 [1] CRAN (R 4.4.0)
##  timechange     0.3.0    2024-01-18 [1] CRAN (R 4.4.0)
##  tzdb           0.4.0    2023-05-12 [1] CRAN (R 4.4.0)
##  urlchecker     1.0.1    2021-11-30 [1] CRAN (R 4.4.0)
##  usethis      * 2.2.3    2024-02-19 [1] CRAN (R 4.4.0)
##  utf8           1.2.4    2023-10-22 [1] CRAN (R 4.4.0)
##  vctrs          0.6.5    2023-12-01 [1] CRAN (R 4.4.0)
##  viridisLite    0.4.2    2023-05-02 [1] CRAN (R 4.4.0)
##  withr          3.0.0    2024-01-16 [1] CRAN (R 4.4.0)
##  xfun           0.46     2024-07-18 [1] CRAN (R 4.4.1)
##  xml2           1.3.6    2023-12-04 [1] CRAN (R 4.4.0)
##  xtable         1.8-4    2019-04-21 [1] CRAN (R 4.4.0)
##  yaml           2.3.9    2024-07-05 [1] CRAN (R 4.4.1)
##  zoo            1.8-12   2023-04-13 [1] CRAN (R 4.4.0)
## 
##  [1] C:/Users/wayne/AppData/Local/R/win-library/4.4
##  [2] C:/Program Files/R/R-4.4.0/library
## 
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