Not showing GOF results on Mediation Path Analysis with controlling variables

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Andrés González

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May 20, 2019, 7:26:12 PM5/20/19
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Hi, 

When i try to run a model to test a mediation effect of a variable called vulnerability (vul), but controlling on socioeconomic (gse_ac3) and economical tightness (estrechez), somehow my model stop showing GOF's

modelo_simple2 <- "# direct effect
             k6_2 ~ c*vul + gse_ac3 + estrechez
             # mediator
             NAQ_sum ~ a*vul + gse_ac3 + estrechez
             k6_2 ~ b*NAQ_sum
             #indirect effect (a*b)
             ab := a*b
             total effect:= c + (a*b)
             "
set.seed(1234)
SEM2 <- sem(modelo_simple2, data=BD_13_02_19, estimator="MLR")
semPaths(SEM2, what="paths", whatLabels="par", layout="tree", thresholds=F, intercepts=F)
summary(SEM2, fit.measures=TRUE, standardize=TRUE, rsquare=TRUE)
fitMeasures(SEM2)
ajusteAFC(SEM2)

 Optimization method                           NLMINB
  Number of free parameters                          9
                                                  Used       Total
  Number of observations                          1914        1995
  Estimator                                         ML      Robust
  Model Fit Test Statistic                       0.000       0.000
  Degrees of freedom                                 0           0
  Minimum Function Value               0.0000000000000
  Scaling correction factor                                     NA
    for the Yuan-Bentler correction (Mplus variant)
Model test baseline model:
  Minimum Function Test Statistic              685.079     476.844
  Degrees of freedom                                 7           7
  P-value                                        0.000       0.000
User model versus baseline model:
  Comparative Fit Index (CFI)                    1.000       1.000
  Tucker-Lewis Index (TLI)                       1.000       1.000
  Robust Comparative Fit Index (CFI)                            NA
  Robust Tucker-Lewis Index (TLI)                               NA


What i'm trying to find if the effect of vulnerability over k2 (psychollogical distress scores) and the mediating effect (Workplace Violence scores), controlling on these 2 variables.  Unfortunatedly, i only get results from this model: 

modelo_simple2 <- "# direct effect
             k6_2 ~ c*vul
             # mediator
             NAQ_sum ~ a*vul + gse_ac3 + estrechez
             k6_2 ~ b*NAQ_sum
             #indirect effect (a*b)
             ab := a*b
             total effect:= c + (a*b)

 lavaan 0.6-3 ended normally after 46 iterations
  Optimization method                           NLMINB
  Number of free parameters                          7
                                                  Used       Total
  Number of observations                          1914        1995
  Estimator                                         ML      Robust
  Model Fit Test Statistic                      23.972      21.018
  Degrees of freedom                                 2           2
  P-value (Chi-square)                           0.000       0.000
  Scaling correction factor                                  1.141
    for the Yuan-Bentler correction (Mplus variant)
Model test baseline model:
  Minimum Function Test Statistic              685.079     476.844
  Degrees of freedom                                 7           7
  P-value                                        0.000       0.000
User model versus baseline model:
  Comparative Fit Index (CFI)                    0.968       0.960
  Tucker-Lewis Index (TLI)                       0.887       0.858
  Robust Comparative Fit Index (CFI)                         0.968
  Robust Tucker-Lewis Index (TLI)                            0.888

Is there a problem on how I'm specifying the variables?


Rplot.jpeg
incorrect model.jpeg

Andrés González

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May 20, 2019, 7:30:00 PM5/20/19
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What literature says is that these covariates (estrechez and gse_ac3) may have confounding effects on the relation of vulnerability over distress, and over the mediating relationship of vulnerability over workplace violence.

Terrence Jorgensen

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May 22, 2019, 2:41:27 AM5/22/19
to lavaan
somehow my model stop showing GOF's

Because the model is saturated (all possible bivariate relationships are estimated as covariances or as slopes).  The model with 2 df omits 2 paths on the mediator.

Terrence D. Jorgensen
Assistant Professor, Methods and Statistics
Research Institute for Child Development and Education, the University of Amsterdam

Andrés González

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May 22, 2019, 8:20:47 AM5/22/19
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Thank you so much Mr Terrence. What do you mean precisely when you say "The model with 2 df omits 2 paths on the mediator.", ¿should I incorporate these paths on the mediator?, ¿is it wrong to have only two degrees of freedom?
Kind regards, 

Terrence Jorgensen

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May 23, 2019, 4:22:32 AM5/23/19
to lavaan
What do you mean precisely when you say "The model with 2 df omits 2 paths on the mediator.", ¿should I incorporate these paths on the mediator?, ¿is it wrong to have only two degrees of freedom?

 Here is an introductory text on SEM.  


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