Ezelius logarithmic disability scale for ME

This is Ezelius proposal for disability/ability scale for myalgic encephalomyelitis (ME).

A logarithmic scale is better than a linear scale at picking up the broad spectrum of ability/disability of persons with myalgic encephalomyelitis (ME). A logarithmic scale acts as a “magnifier” that magnify differences in already small values, which is a desirable characteristic because there is no limit how bad a person with ME can get. Already, at a very low level of function it is always possible to get worse, or find a person that is worse off.

The proposed way to grade disability would be according to this scale:

“disability level” = -log2 (“relative energy level”)

and to obtain the relative energy level from the scale is done as follows:

“relative energy level” = 2-(“disability level”) = 1/2“disability level”

For example, a disability level of 4 would correspond to having 1/16 (approximately 3%) of the healthy energy level.

One step on the disability level scale corresponds to halving the energy level. For example going from disability 2 to 3, means that the energy level goes from 1/4 to 1/8.

One can use decimals of the disability level, for example 3,5 for somebody that is between 3 and 4, or 3,3 for somebody with 10% energy level ( -log2(0,10) =~ 3.3 ).

Here, energy means the total amount of “useful” energy for mental and physical activity; in other words: the mean daily achievable mental and physical activity level. The average should be over at least two weeks in order to average out the effects of varying ability (push-and-crash cycle, post exertional relapse, etc) typical in ME.

Dis­­abil­­ity level Energy Energy Example
0 1 100% Fully functional. Can work full time, cook own food, clean the own house and still have energy for leasure acitivities.
1 1/2 50% Usually can not work full time. In some cases, light work full time can be maintained, if resting during spare time (including week-end) and no cooking or house cleaning.
2 1/4 25% Can leave the house on a daily basis, but only for two hours a time.
3 1/8 12,5% House bound most of the time, but can leave the house about 1-2 hours about 2-4 times a week.
4 1/16 6,25% House bound most of the time, but can leave the house about one hour once a week. Can cook easy meal occationally.
5 1/32 3,125% House bound. Need help to cook food. Can shower about two times a week.
6 1/64 1,15625% Usually bed bound, but can visit toilet at times.
7 1/128 0,78125% Bed bound. Can not visit the toilet. Can only speak few words. Can only tolerate sound, light, touch for short periods at a time.
8 1/256 0,390625% Bed bound. Can not tolerate sound, light, touch. Need to be left alone.

There are most physical activities listed in the examples above. It had been more satisfactory if also mental activities had been listed, but I think it is harder. Partly because it depends whether the activities are made in a quiet environment without distractions or not. Partly because it depends on the persons prior mental capacity. And partly because it is difficult to quantify. How many pages can one read in a book? How complicated can the text be? How much is retained of the text that was read?

/Kasper Ezelius, 4th of November 2018, Örebro, Sweden