THE EFFECT SIZES IN A MEDIATION MODEL

Effect size is the amount of variance explained in the mediation model contributed by every single path. The researcher might be interested to know the relative contribution of individual paths in the mediation model, especially the effect of a mediator on the dependent variable. The researcher could assess the effect size for every path in the model, and also the mediated effect of the moderator variable itself. Specifically, the two effect sizes are:

(1) The R2 Measures the effect size of individual path in the model (3 paths)
(2) The R2 Measures the size of mediated effect of a mediator in the model
The range of values of R2 and its relative effect size based on definition by Cohen (1988) is given in Table 2.

1) R2 measures for the individual path in the mediation model is defined as follows
     i) r2XM represents the squared partial correlation between the X and M variables in the model,
     ii) r2XY denotes the squared partial correlation between X and Y variables in the model,
    iii) r2MY.X corresponds to the squared partial correlation between the M and Y variables with the influence of X removed,
 
For the above example - the following measures are obtained:
   i) The effect size of Skills & Training (X) on Job Attitude (M) is 0.78 (Figure 1)
  ii) The effect size of Skills & Training (X) on Career Advancement (Y) is 0.59 (Figure 2)
  iii) The effect size of Job Attitude (M) on Career Advancement (Y), controlling for X
This is equivalent to r2XMY - r2XY = 0.67 – 0.59 = 0.08 (Note: r2XMY=0.67 - Figure 1)
Conclusion: The effect size of a mediator on DV in small range

2) R2 Measures for the mediated effect of the mediator (Job Attitude).
This value is computed using the following formula:
R2MY – (R2 XMY - R2XY)
Where:
R2XY is the R2 for the model containing X and Y only (Figure 2)
R2MY is the R2 for the model containing M and Y only (Figure 3)
R2 XMY is the R2 for the model containing all X, M, and Y (Figure 1)
R2MY – (R2 XMY - R2XY)
0.66 – (0.67-0.59) = 0.58

Thus, based on Cohen (1988), the mediated effect size of the mediator Job Attitude in the relationship between Skills & Training and Career Advancement is in large range. 

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The Steps In Performing Second Order CFA

The procedure of performing the second order factor analysis is as follows:

Step 1: Run the CFA for all first order latent sub-constructs (measurement model) 
In this step, the researcher is running CFA for the measurement model of sub-constructs.

Step 2: Run the Second Order CFA for the main construct on its sub-constructs
In this step, the researcher estimate the causal effects from the main construct to all its sub-constructs. The estimation is carried out by linking the main construct to all sub-constructs using a single headed arrow. The objective here is to estimate the factor loading of main construct on its sub-constructs in order to confirm that the theorized second order construct loads into the respective sub-constructs.

Amacam? Ada yang sudah pening kepala? ;-) Sabar, sabar. Jangan pening-pening kepala. Jom ikuti kursus yang akan kami adakan ini ;

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Date	››	21 November 2013 (Thursday)
Time	››	8:30am – 5:30pm
Venue	››	Wisma R&D, Universiti Malaya
Speaker	››	Dr. Mohd Awang Bin Idris
Fee	››	RM180 (normal rate) - payment from 21 October 2013 until closing date
Medium	››	Bahasa Malaysia

 

CCOMPUTING THE EFFECT SIZES IN A MEDIATION TEST

Supposed we are working with the following model (Figure 1). In this model, the researcher is interested to carry out the following analysis:

1) To determine whether Job Attitude mediates the relationship between Skills & Training and Career Advancement.
2) To measure the effect size for single every path in the model
3) To measure the mediated effect of the mediator in the model

 

Figure 1: The model containing all constructs namely Skill & Training (X), Job Attitude (M), and Career Advancement (Y).

The coefficients and their probability values are summarized in Table 1. As discussed earlier, these values can be used to determine the significance of a mediator in the mediation model.

More explaination, please join our workshop:

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Date	››	21 November 2013 (Thursday)
Time	››	8:30am – 5:30pm
Venue	››	Wisma R&D, Universiti Malaya
Speaker	››	Dr. Mohd Awang Bin Idris
Fee	››	RM180 (normal rate) - payment from 21 October 2013 until closing date
Medium	››	Bahasa Malaysia