Monday, September 6, 2010

Score 100/100 on the SF-36 PF subscale and still satisfy empiric criteria forCFS

In the Switzer et al (2010) study on XMRV and CFS, one or more CFS patients scored 100 (out of 100) on the SF-36 physical functioning scale.

That means they answered "No, not limited at all", to all of the questions below (the questions below are the questions for the physical functioning subscale: basically "Yes, Limited A Lot" gets you 0 points for that question; "Yes, Limited A Little" gets you 5 and "No, not limited at all" gets you 10 so scale is 0-100).

Extract from Switzer et al (2010) study paper:
SF-36 physical functioning 65.5, range 10-100
This average score is higher than you generally see in CFS studies.

Leonard Jason previously noted this problem in:
5. Jason LA, Najar N, Porter N, Reh C. Evaluating the Centers for Disease Control's
empirical chronic fatigue syndrome case definition. Journal of Disability Policy Studies
2009;20;93.

Leonard Jason et al gave an example of a woman with major depressive disorder who didn't have CFS satisfying the empiric criteria despite having a SF-36 PF score of 100.  I mentioned this in my letter in Psychosomatic Medicine (which I can't post for copyright reasons).

Tom




SF-36 physical functioning questions

4. The following items are about activities you might do during a typical day. Does your health now limit you in these activities? If so, how much?
(check one on each line) ACTIVITIES

Yes, Limited A Lot

Yes, Limited A Little

No, Not Limited At All

a. Vigorous activities, such as running, lifting heavy objects, participating in strenuous sports
􀂆 1
􀂆 3
􀂆 5

b. Moderate activities, such as moving a table, pushing a vacuum cleaner, bowling, or playing golf
􀂆 1
􀂆 3
􀂆 5

c. Lifting or carrying groceries
􀂆 1
􀂆 3
􀂆 5

d. Climbing several flights of stairs
􀂆 1
􀂆 3
􀂆 5

e. Climbing one flight of stairs
􀂆 1
􀂆 3
􀂆 5

f. Bending, kneeling, or stooping
􀂆 1
􀂆 3
􀂆 5

g. Walking more than a mile
􀂆 1
􀂆 3
􀂆 5

h. Walking several blocks
􀂆 1
􀂆 3
􀂆 5

i. Walking one block
􀂆 1
􀂆 3
􀂆 5

j. Bathing or dressing yourself
􀂆 1
􀂆 3
􀂆 5

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