Measurement information

During the development of the SFInX in people recovering from a proximal humeral fracture, measurement properties of the SFInX (such as convergent validity and intra-rater reliability) have been thoroughly tested and evaluated. With Rasch analysis we evaluated the structure of the SFInX, its (uni)dimensionality, item difficulties and estimations of individuals’ shoulder function. Also through Rasch analysis, an interval-level (ruler-like) scale from 0 to 100 was created.

Here we present an overview of measurement information.

  • Hierarchy of SFInX items (by difficulty of activity)
  • Measurement properties
  • Rasch converted SFInX scores

Based on the difficulties of the 13 SFInX items, the hierarchy of items would be as below.

Hierarchy of items



ITEM 3 washing back opposite shoulder
ITEM 6 washing lower back
ITEM 12 moving an object above head level
ITEM 13 throwing a ball with two hands overhead
ITEM 4 combing hair/running hand through hair
ITEM 8 reaching behind to get an object
ITEM 10 carrying a heavy object with two hands
ITEM 11 placing an object on a shelf at shoulder level
ITEM 5 tucking shirt into pants
ITEM 9 holding an object for a longer period
ITEM 2 washing opposite armpit
ITEM 7 lying on affected side
ITEM 1 drinking from a cup

An overview of the measurement properties of the SFInX for people recovering from a proximal humeral fracture can be found below in the Table “SFInX measurement properties”

SFInX measurement properties
Content validity SFInX items have been linked to the WHO International Classification of Functioning, Disability and Health (see SFInX User Manual)
Face validity SFInX items have been generated and endorsed by orthopaedic surgeons, physiotherapists and occupational therapists
Construct validity
Structural validity 66.3% of total variance was explained by the 13 items Rasch analysis confirmed unidimensionality
Convergent validity Pearson’s r = 0.73 to 0.89 with other shoulder measures
Discriminant validity Pearson’s r = -0.08 with different construct (cognition)
Known-groups validity 33.7 points difference (95%CI 21.0 to 46.3; t=-5.37, p<0.01) between people less than 3 months post-fracture compared to people more than 9 months post-fracture
Longitudinal validity (responsiveness) Pearson’s r (change scores) = 0.40-0.49 with other shoulder measures, indicating the SFInX being more responsive to change
Internal consistency Person separation index was 2.90, person reliability of 0.89Item separation index was 6.10, item reliability of 0.97
Test-retest reliability ICC2,1(agreement) = 0.96 (95%CI 0.94 to 0.97)
Measurement error SEM = 3.9 / 100 points
Minimal Detectable Change MDC95 = 10.8
Inter-rater reliability ICC2,1(agreement) = 0.91 (95%CI 0.63 to 0.97)
Measurement  error SEM = 5.8 / 100 points
Clinically important difference
Minimal 10-12 / 100 points
Moderate 17 / 100 points

Rasch converted SFInX scores

Using Rasch analysis, raw (ordinal) scores were converted into SFInX scores which created an interval-level (ruler-like) scale of shoulder function.

Minimum score:  0 points = 0 SFInX score

Maximum score: 21 points = 100 SFInX score


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