In order to measure how well a device is or a person deals with a given vehicle, many people work on predefined obstacle courses. Kilkens et al. reviewed a wide array of wheelchair skill tests, aimed to asses the ability to propel and maneuver a wheelchair under standardized
and/or simulated conditions of daily living. Skills included in the 24 tests in order of frequency were:

- Wheelchair propulsion, assessed in terms of period of time, a fixed distance or longest distance possible.
- Transfer from and to the wheelchair, usually examining the performance in different transfers.
- Negotiation of kerbs, with kerb's height ranging from 0.025 to 0.15m, and some requiring ascending and descending the kerb.
- Ascending slopes, defined in terms of inclination (ranging from 1 to 11 degrees) and length (ranging from 3 to 21m).
- Traversing tracks, e.g. slalom, figure of eight and obstacle course.
- Sprinting over a fixed distance (ranging from 6.5 to 30m).
- Performing a wheelie was also a skill included in few of the tests assessed.
- Half of the tests included other specific wheelchair skills, e.g. managing brakes, negotiating doors or loading the wheelchair into a car.

In eight of these tests, wheelchair skills were a part of a broader measure of ADL skills like eating, bed mobility skills and washing hands. Ideally, tests have to be as efficient and as short as possible, and should not require much space or special equipment. The VFM or the TAMP take like 1 hour to complete, while the WST needs only 30 min.

The most common outcome of these tests are values like task performance time, Physical strain, Independence in performance, distance covered in propulsion, endurance and other subjective ratings like perceived difficulty. Kilkens argues that tests should have preferably a simple scoring system, convenient to use and easi to analyze. It is important to note that these metrics can be applied mostly to obstacle courses but usually not to daily living, as they are measured over a given time and trajectory.



The main problem with most of these courses is that they require a large space and investment to build structures just according to specifications. Furthermore, they are used to measure skills in controlled situations, rather than in everyday ones. Still, they are widely used because they provide a benchmark to test most wheelchairs models.

First things first, before having someone drive a prototype, it is important to know about his/her condition. Of course, the doctor is the main source of information, but in order to process results afterwards, some index is always useful, we are engineers, after all!!. The key is to obtain a quantified disability profile to correlate this data with the amount of help they may require, demand or receive.

Disability is technically defined as a lack of ability relative to a personal or group standard or norm, but, in fact, there is often simply a spectrum of ability. It may involve physical, sensory, cognitive or intellectual impairment, mental disorder and/or various types of chronic disease.

In experimental work, though, it is better to define disability as the degree of difficulty to independently perform basic Activities of Daily Living (ADL) [Katz]. Disability is not an attribute that is clearly present or absent, but rather a matter of degree.

One of the best ways to obtain global information about patient needs is represented by the multi-dimensional approach and, in particular, in case of elderly patients the most common approach is the CGA, a multidimensional process designed to assess an elderly person's functional ability, physical health, cognitive and mental health, and socio-environmental situation. It includes different disability scales to evaluate the cognitive and physical state and condition of individuals. Here are the most popular ones.

The MMSE or Folstein test [Crum] is a brief 30-point questionnaire test that provides a quantitative measure of cognitive status in adults. Any score
over 27 (out 30) is effectively normal, event though it changes depending on age and education. In the time span of about 10 minutes, it samples various functions, including arithmetic, memory and orientation.

IADL, also called Lawton's scale [Lawton], is based on a questionnaire to evaluate the capacity of the subject to perform daily tasks ruled by cognitive functions (judgement, language, orientation, calculation, memory, planning). Thus, IADL measures the degree of autonomy of an elderly individual. This test appears complementary to MMSE, that rather evaluates cognitive functions. For example, a subject with memory disorders or difficulty of calculating shows a reduced score. 4 tests are particularly important since they are well correlated with cognitive functions evaluated by the MMSE test. They include the ability to : i) Use telephone; ii) Use transportation; iii) Take medication; and iv) Handle finances. For example, using a telephone under his own initiative is related to the intention and planning of a task (to look up the name of somebody in a phone book) and to the comprehension of language (to have a conversation). On the other hand, to be limited to a small number of well known phone numbers or to answer the telephone without calling implies automatic mechanisms. An evaluation of these 4 activities allows early detection of cognitive deterioration, several years (approximately 3 to 5) before a dementia is diagnosed. Detection of an alteration of at least one of these 4 activities calls for a more precise neurological assessment.

The GDS [Yesavage] is a self-report inventory, constructed to assess depression and general well-being in the elderly. It is a brief questionnaire in which
participants are asked to respond yes/no to 30 questions in reference to how they felt on the day of administration. Scores of 0-9 are considered normal, 10-19
indicate mild depression and 20 - 30 indicate severe depression.

The Barthel Index [Mahoney] consists of 10 items that measure a person's daily functioning, specifically ADL and mobility. Items can be divided into a
group that is related to self-care (feeding, grooming, bathing, dressing, bowel and bladder care, and toilet use) and a group related to mobility (ambulation, transfers, and stair climbing). The maximum score is 100 if 5-point increments are used,
indicating that the patient is fully independent in physical functioning. The lowest score is 0, representing a totally dependent bedridden state.
Apraxia is a neurological disorder characterized by loss of the ability to execute or carry out learned purposeful movements, despite having the desire to and the physical ability to perform the movements. It scores from 0 (worse result) to 10.

I know, I know. It's a Russian thing.
When we're about to do something stupid,
we like to catalog the full extent
of our stupidity for future reference.
- S. Ivanova, A Voice in the Wilderness

And just when everything seems to be going so well, someone always asks, "so, what is so special about your work?". For scientists, a simple "it works" does not seem enough, so everyone stomps into the field of metrics sooner or later. Inventing some metrics of your own, while obviously appealing, will just not do. Since words might do you no good either, this is the point where standards come handy. The key idea here is that we are good as long as our system behaves better than previous, similar ones in at least a few in quantifiable aspects.



When one starts to look for standard standards in the wheelchair navigation field, bad news come first: there seems to be no established one to measure wheelchair performance -specially regarding power wheelchair navigation and, more specifically, shared control-. Fortunately, there is a large number of proposals that more or less agree regarding parameters of interest in assisted navigation (e.g. [webster et al, 88]).

Assisted wheelchair navigation is a field where many fields converge, from cognitive sciences to medicine, and all the way through engineering. Consequently, trying to fit all related metrics in the same bin would be like trying to explain feelings with differential equations. Instead of doing so, we will go for a tentative distinction between different categories, which might be more or less correlated, but are simpler to explain separately. Keep in this channel for the categories very soon in a web near you :)