This study was designed to develop and psychometrically validate the Shoulder Problems
Assessment Scale (SPAS), a patient-reported outcome measure intended to assess
shoulder-related functional limitations in adults. SPAS was developed to address
limitations of existing shoulder scales related to cognitive burden, cultural relevance,
and response format, particularly in populations with varying health literacy levels.
The development process followed a four-stage methodological framework. In the first
stage, the conceptual framework and initial item pool were established through a
comprehensive literature review, semi-structured interviews with patients experiencing
shoulder problems, and input from experienced physical therapists. These steps aimed to
identify daily activities that commonly provoke functional difficulty in routine life. An
initial pool of 34 items was generated, including activity-based items structured in a
hierarchical stepwise yes/no format.
In the second stage, content validity was evaluated by an expert panel using the Lawshe
method. Items with insufficient content validity or conceptual overlap were revised,
combined, or removed. A pilot study was then conducted to assess item clarity, cultural
appropriateness, and comprehensibility. Based on expert feedback and pilot results, the
item pool was refined and prepared for the main application.
The third stage consisted of a multicenter field application conducted in physical
therapy units across multiple regions of Turkey. SPAS was administered to individuals
with shoulder problems, followed by the Turkish version of the Shoulder Pain and
Disability Index (SPADI) for concurrent validity assessment. A subgroup of participants
with stable clinical status completed SPAS again after 3-7 days to evaluate test-retest
reliability.
In the final stage, psychometric analyses were performed. Construct validity was examined
using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) with a
robust diagonally weighted least squares estimator appropriate for the hierarchical
response structure. Reliability was assessed using internal consistency coefficients and
intraclass correlation coefficients. Concurrent validity was evaluated through
correlations with SPADI scores. Receiver operating characteristic (ROC) analysis was
conducted to determine a clinically interpretable cut-off value for SPAS using a
SPADI-derived functional limitation reference.
SPAS consists of 12 activity-based items, each comprising four ordered difficulty levels.
Respondents indicate the level at which difficulty first appears, reflecting a
threshold-based approach to functional limitation rather than graded symptom intensity.
Total scores range from 0 to 48, with higher scores indicating greater functional
limitation. The study aims to provide a valid, reliable, and practical instrument for
assessing shoulder-related functional limitations in clinical and research settings.
