Table 1 

Comparative measurement range of five physical function instruments with 90% reliability 

PF10 
HAQ 
PROMIS PF10 
PROMIS PF20 
PROMIS PF CAT10 



Floor 
2.5 
4.5 
2.9 
4.5 
4.5 
Ceiling 
0.2 
0.4 
0.2 
0.2 
1.2 
Range 
2.3 
4.1 
3.1 
4.8 
5.7 


Each unit below zero (the population mean) is scored as a negative of standard deviations toward the floor, and each unit above zero (the population mean) is a standard deviation in the direction of the ceiling "range" as the algebraic sum of standard deviations of positive and negative [15]. ^{1 }Instruments: PF10  10item physical function scale of the SF36 [3]; HAQ  20item Health Assessment Questionnaire [2]; PROMIS PF10  PROMIS PF10, 10item Physical Function assessment form [5]; PROMIS PF20  PROMIS PF20, 20item physical function assessment form [5]; PROMIS PF CAT10  PROMIS PF 10item Computerized Assessment Testing [5] 

Bruce et al. Arthritis Research & Therapy 2013 15:R144 doi:10.1186/ar4327 