Table 2 Steps in Exploratory Factor Analysis (EFA)

Aim

Outcome/conditions

Step 1

Item deletion

• If ≥95% of the responses on an item was located in one response category

• If ≥20% of the responses on an item was located in the ‘not applicable’ category AND this was specific to a subgroup

Step 2

Item deletion

• If an item correlated ≤0.2 with ≥80% of the other items

• If two items correlated ≥0.9

Step 3

Test assumptions PCA

• Adequate sample size if Kaiser-Meyer-Olkin value >0.6

• Items were correlated if Bartlett’s test of sphericity p < 0.05

Step 4

Explore number of factors

• Outcome on Catell’s scree test

• Outcome on Parallel Analysis

Step 5

Determine rotation for factor structure

• Outcome rotation (e.g. varimax, Quartimax, Direct Oblimin)

Step 6

Determine number of factors and items

• Analyzed per outcome of step 4: the number of items, item content, and item factor loadings

• Assigned to a factor: items with factor loading >0.5

Item deletion

• If item had a factor loading of <0.5

• If item had factor loadings of >0.3 on more factors: deletion discussed based on importance of item

Step 7

Item deletion

• If inter-item correlation ≥0.7

• If item had low inter-item correlation (0.2–0.4) with half of the items in the factor

• If Cronbach’s alpha <0.7

Final QWLQ-CS