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Table 3 For each item which was omitted during the single-scale analyses, hypotheses regarding possible reasons for misfit were formulated, modeled and tested as specified

From: Confirmatory factor analysis of the thyroid-related quality of life questionnaire ThyPRO

Item

Hypothesized reason for misfit

Investigative modeling of the hypothesized reason for misfit

Results of the investigative modeling

2b Visible swelling on neck from the Goiter Symptoms scale

May relate to cosmetic concerns, rather than being a symptom

Item was allowed to cross-load on the Cosmetic Complaints factor

Loaded –0.23 on the Cosmetic Complaints factor.

Loading on own factor: 0.68

2e Throat pain felt in ears from the Goiter Symptoms scale

May be relevant only for patients with subacute thyroiditis, during the acute inflammatory phase.

No marker of acute inflammation is available in the clinical database describing the patients. Only 9 patients in this sample had subacute thyroiditis

Extraneous modeling not possible.

Loading on own factor in the full model: 0.75

2l Hoarseness from the Goiter Symptoms scale

Hoarseness is also a classical symptom of hypothyroidism. Might relate more to hypothyroidism than to goiter.

Item was allowed to cross-load on the Hypothyroid Symptoms factor

Loaded 0.22 on Hypothyroid Symptoms factor.

Loading on own factor: 0.46

2t Loose stools from the Hyperthyroid Symptoms scale

Might be a non-specific physical symptom

Item was allowed to load on the other physical symptoms factors, except for Eye Symptoms

Loaded –0.15 on Goiter Symptoms factor and –0.55 on Hypothyroid Symptoms.

Loading on own factor: 1.20

6d Afraid of being seriously ill from the Anxiety scale

May be related to not being fully examined yet, and thus an initial fear of e.g. cancer has not yet been ruled out completely

Item was regressed on time since diagnosis.

A significant negative association with time since diagnosis was found

10e Other people lack understanding from the Impaired Social Life scale

May relate more to depressive mood and emotional distress than the other items in the Social Life scale

Item was allowed to cross-load on the Depressivity and the Emotional Susceptibility factor

No significant loading on Depressivity or Emotional Susceptibility was found.

Loading on own factor: 1.08

13g Felt too fat from the Cosmetic Complaints scale

Weight gain is often experienced during hypothyroidism. Feeling too fat may also relate more to a negative self-esteem aspect of depressive mood

Item was allowed to cross-load on the Hypothyroid Symptoms and Depressivity and Anxiety factors

Loaded –0.16 on Hypothyroid Symptoms factor, –0.22 on Anxiety and 0.15 on Depressivity factor.

Loading on own factor: 0.53