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Table 2 Steps in Exploratory Factor Analysis (EFA)

From: The quality of working life questionnaire for cancer survivors (QWLQ-CS): factorial structure, internal consistency, construct validity and reproducibility

Input: 104-items preliminary QWLQ-CS
  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
Output: Final QWLQ-CS