The evaluation of change in pain intensity: a comparison of the P4 and single-item numeric pain rating scales.
METHODS
Prospective observation study.


OBJECTIVE
To compare the test-retest reliability and longitudinal validity (sensitivity to change) of 2 single-item numeric pain rating scales (NPRSs) with a 4-item pain intensity measure (P4).


BACKGROUND
Pain is a frequent outcome measure for patients seen in physical therapy; however, the error associated with efficient pain measures, such as the single-item NPRS, is greater than for self-report measures of functional status. Initial evaluation of the P4 suggests that it is more reliable and sensitive to change than the NPRS.


METHODS
Two single-item NPRSs and the P4 were administered on 3 occasions--initial visit (n = 220), within 72 hours of baseline (n = 213), and 12 days following baseline assessment (n = 183)--to patients with musculoskeletal problems receiving physical therapy. Reliability was assessed using a type 2,1 intraclass correlation coefficient. Longitudinal validity was assessed by correlating the measures' change scores with a retrospective rating of change that included patients' and clinicians' perspectives.


RESULTS
The test-retest reliability and longitudinal validity of the P4 were significantly greater (P1<.05) than both single-item NPRSs. Minimal detectable change of the P4 at the 90% confidence level was estimated to be a change of 22% of the scale range (9 points) compared to 27.3% (3 points) and 31.8% (3.5 points) for the 2-day NPRS and 24-hour NPRS, respectively.


CONCLUSIONS
The findings of this study suggest the P4 is more adept at assessing change in pain intensity than popular versions of single-item NPRSs.
Spadoni
Gregory F
GF
ProActive Physiotherapy Clinic, Hamilton, Ontario, Canada. spadoni@mountaincable.net
Stratford
Paul W
PW
Solomon
Patricia E
PE
Wishart
Laurie R
LR
D000328:Adult; D015331:Cohort Studies; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D009140:Musculoskeletal Diseases / Q000175:diagnosis / Q000534:rehabilitation; D010146:Pain / Q000175:diagnosis* / Q000453:epidemiology / Q000534:rehabilitation; D010147:Pain Measurement / Q000379:methods*; D011446:Prospective Studies; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires