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Table 1 Reasons for item exclusion at each stage of instrument development

From: The de Morton Mobility Index (DEMMI): An essential health index for an ageing world

Excluded item Reason for exclusion
Pilot testing of 51 mobility items: 9 items excluded due to practical limitations
Number of times in/out of bed in 10 sec Removed to maximise patient safety. Difficult to test for patients who have drips, drains, indwelling catheters etc. A similar item, 'lying to sitting independently within 10 seconds' was deemed to be safer and provided similar clinical information.
Sit to stand 3 times in 10 seconds To reduce the burden of testing by minimising redundancy of sit to stand items. 'Independent sit to stand in 3 seconds' was retained due to shorter administration time.
Sitting balance and turning head Many patients had significantly limited cervical range of movement and therefore this test was difficult to standardise across patients.
Reach sideways to pick up pen from floor (sitting) Several patients reported feeling dizzy performing this task after first attempting to reach forward to pick up pen from floor. Reaching forwards to pick up a pen was considered to be the more functional item and was therefore retained.
Reach sideways to pick up pen from floor (standing) As above
Walk 6 meters in 10 seconds Requires a standardised walking test environment which could not be relied upon.
Step test Requires a standardised step. Removed due to equipment requirements.
Step Requires a standardised step. Removed due to equipment requirements.
Step over box Requires a standardised step. Removed due to equipment requirements.
Testing of 42 mobility items: 8 items excluded due to practical limitations
Skipping This is a complex movement that required practice to perform in a standardised way.
Sit to stand using the chair seat (not using the arms of the chair) For wider patients there was not enough space to push up from the seat. Cognitively impaired patients found this task difficult to understand when the arms of the chair were accessible.
Immediate standing balance Required significant explanation, particularly for cognitively impaired patients.
Semi tandem stance Required significant explanation and/or demonstration for patients to understand task.
Reach in sitting Dizziness prevented some patients from successfully completing this item.
360 degree turn This item was difficult to perform with patients who had lines, drips, drains etc.
Sit to lie Asking the patient to return to bed to assess this item interrupted the flow of testing.
Hop This is a dynamic single leg activity and was removed to maximise patient safety.
Reframing walking items to remove potential for local item dependence (assumption of Rasch analysis)
Four walking items: 5 m, 10 m, 20 m and 50 m (response options were levels of assistance for each distance) 4 walking items replaced with 2 items:
  1. walks +/- gait aid (with distance response options)
  2. walking assistance (with levels of assistance for response options)
Rasch analysis of 32 mobility items: 4 items removed
Transferring from bed to chair Required equipment and had similar threshold locations to other items
Carrying a glass of water while walking Required equipment and had similar threshold locations to other items
Timed bed transfer Required equipment and had similar threshold locations to other items
Timed chair transfer Required equipment and had similar threshold locations to other items
Removal of items that provided similar clinical information (and to avoid local item dependence): 8 items removed
Sitting arm raise Similar items: Sitting unsupported and sitting arm raise
  'Sitting unsupported' is a simpler test and maximises scale width as it has the lowest logit item score (easiest item).
×5 sit to stand without arms Similar items: ×1 sit to stand without arms and ×5 sit to stand without arms.
'x1 sit to stand without arms' is a simpler and quicker test.
Standing arm raise Standing with eyes closed Similar items: Standing unsupported, standing arm raise and standing with eyes closed.
'Standing unsupported' is the simplest test and is an important component of independent mobility.
Standing with feet together eyes closed Similar items: Standing with feet together and standing with feet together eyes closed
  'Standing with feet together' is a simpler test.
Tandem standing Tandem walking Similar items: Tandem standing, tandem standing with eyes closed and tandem walking
  'Tandem standing with eyes closed' had the second highest item logit location (second most difficult item) and was therefore retained to maximise scale width.
Stand on one leg Similar items: Stand on one leg and stand on one leg eyes closed
  'Stand on one leg with eyes closed' had the highest item logit location (most difficult item) and was therefore retained to maximise scale width.
Rasch analysis of 20 mobility items: 3 items removed
Toe walk Similar threshold locations to other items and statistically significant misfit
Heel walk Similar threshold locations to other items and statistically significant misfit
Sideways walking Similar threshold locations to other items and statistically significant misfit