Rasch analysis of UK FIM+FAM in patients with TBI
Adapted from the original US version, the UK Fun-
ctional Assessment Measure (UK FIM+FAM) was first
published in 1999 (7). The 30-item scale comprises 16
motor items (including self-care and mobility) and 14
cognitive items (including communication, cognition
and psychosocial adjustment).
The UK Rehabilitation Outcomes Collaborative
(UKROC) (8) provides the national clinical database
for all specialist in-patient rehabilitation services in
England. These services cater for a selected population
of patients with severe complex neurological disabi-
lity. The UK FIM+FAM is the principal measure of
functional outcome within the dataset and, since 2013,
its collection is a mandated requirement for reimburse-
ment within these services. It is therefore pertinent to
understand its psychometric properties in this context.
In addition, transformation of the scale from ordinal
to interval-level data (using techniques such as Rasch
analysis (9–11)) confers theoretical advantages for
clinical practice, potentially increasing sensitivity by
stretching the existing ogive raw score points at both
the upper and lower margins, as well as enabling the
calculation of valid change scores.
Traditional psychometric evaluations of the UK
FIM+FAM in both a general neuro-rehabilitation
cohort and in stroke patients (12, 13) have shown the
UK FIM+FAM to have 3 distinct subscales: Motor,
Communicative, and Psychosocial. Two studies from
the 1990s have explored the linear Rasch transforma-
tion of the original US FIM+FAM scale following TBI
and showed partial conformation to the Rasch model
(14, 15). However, approaches to Rasch analysis have
changed significantly in the last 20 years (16), and as
yet there are no published Rasch analyses of the UK
FIM+FAM scale in patients with TBI.
Our recent Rasch analysis of the UK FIM+FAM in
patients with complex disability following stroke (17)
provided evidence for uni-dimensionality. It showed
that the best fit was achieved where responses for the
16-item ”Motor”, 5-item ”Communicative” and 9-item
”Psychosocial” subscales were summarized into 3 su-
per-items, and were split for left and right hemisphere
stroke location due to differential item functioning
(DIF). This approach satisfied the expectations of the
Rasch model without the need for re-scoring of item
thresholds or exclusion of extreme scores.
The aim of this study was to determine whether the
UK FIM+FAM fits the Rasch model in patients with
complex disability following TBI in a similar manner
to patients with stroke, and if so, to derive a conver-
sion table of Rasch-transformed scores for potential
clinical use.
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METHODS
Setting and participants
In the UK, rehabilitation services are broadly categorized on 3
levels (18). Following TBI, the majority of patients will have
relatively simple rehabilitation needs and make a good recovery
with the support of their local (Level 3) rehabilitation services.
However, a smaller number have more complex disability
requiring specialist rehabilitation in either local district (Level
2) or regional (Level 1) rehabilitation services. The UKROC
database provides the national clinical database for all Level
1 and 2 rehabilitation services in England. The study sample
therefore represents a selected group of adults with complex
disability following severe brain injury.
Principles of approach
Where an instrument is already established in clinical use and
the content and ordinal scoring system have some meaning for
clinicians, a balance may need to be found between maintaining
the integrity of the scale and finding the best fit solution for a
transformed scale. In addition, patients with complex disability
following TBI form a more diverse patient group than stroke
patients, with deficits ranging from ambulant patients with
highly challenging behaviours to severe physical disability. The
diversity of this sample represents a challenge for the psycho-
metric properties of the FIM+FAM. Hence, we expected that
this analysis might not fit the Rasch model quite as readily as
in more homogeneous conditions.
UK FIM+FAM
The 30 items of UK FIM+FAM are each scored on a 7-point
ordinal scale as follows: 1 (Total assistance); 2 (Maximal as-
sistance); 3 (Moderate assistance); 4 (Minimal assistance);
5 (Supervision/set-up); 6 (Independent with device); and 7
(Fully independent). A category of 6 or 7 implies no help from
another person, whilst assessment for categories 1 to 4 is often
based on frequency of intervention. Like the US version, the
FIM components of the UK FIM+FAM are retained in order
to maintain comparability for that component of the scale with
units that use the FIM only. Amongst the FAM items, 3 are
structurally different in the UK version (1999) compared with
the original US version (1994): ”Concentration”’ replaces ”At-
tention”; ”Safety awareness” replaces ”Safety judgement”; and
”’Use of leisure time” replaces ”’Employability”. The rationale
for these differences is described in the 1999 source paper for
the UK FIM+FAM.
Data source
The data source for this analysis was the UKROC database,
which was initially set up by a National Institute for Health
Research Programme Grant (19). It is now commissioned
directly by NHS England to provide the national clinical and
commissioning database for specialist inpatient rehabilitation
in England. The dataset comprises socio-demographic and
clinical data as well as information on rehabilitation needs,
inputs and outcomes on admission and discharge from inpa-
tient rehabilitation. Reporting of UK FIM+FAM data has been
a commissioning requirement for Level 1 and 2 rehabilitation
J Rehabil Med 51, 2019