Chapter 16 Omega
Omega is considered a measure of internal consistency and can, if a number of assumptions are met, estimate the reliability of a set of items.
16.1.1 Example dataset
This example uses the Rosetta Stats example dataset “pp15” (see Chapter 1 for information about the datasets and Chapter 3 for an explanation of how to load datasets).
16.2 Input: jamovi
In the “Analyses” tab, click the “Factor” button and from the menu that appear, select “Reliability Analysis” as shown in Figure 16.1.
In the box at the left, select all variables you want to include in this analysis and move them to the box labelled “Items” using the button labelled with the rightward-pointing arrow as shown in Figure 16.2.
Select the checkbox labelled “Omega” in the left-most column at the bottom labelled “Scale Statistics”, as shown in Figure 16.3.
You can now also order additional statistics, such as the value Omega would have if you were to omit each item, as shown in Figure 16.4.
16.3 Input: R
::reliability( rosettadata = dat, items = c( "highDose_AttGeneral_good", "highDose_AttGeneral_prettig", "highDose_AttGeneral_slim", "highDose_AttGeneral_gezond", "highDose_AttGeneral_spannend" ));
16.6 Output: R
16.6.1 R: rosetta
126.96.36.199 Reliability analysis
188.8.131.52.1 Scale structure
184.108.40.206.1.1 Scale structure
220.127.116.11.1.1.1 Information about this scale
|Items:||highDose_AttGeneral_good, highDose_AttGeneral_prettig, highDose_AttGeneral_slim, highDose_AttGeneral_gezond & highDose_AttGeneral_spannend|
|Number of correlations:||10|
|Percentage positive correlations:||100|
18.104.22.168.1.1.2 Estimates assuming interval level
|Revelle’s Omega (total):||0.79|
|Greatest Lower Bound (GLB):||0.87|
Note: the normal point estimate and confidence interval for omega are based on the procedure suggested by Dunn, Baguley & Brunsden (2013) using the MBESS function ci.reliability, whereas the psych package point estimate was suggested in Revelle & Zinbarg (2008). See the help (‘?ufs::scaleStructure’) for more information.