This study endeavoured to determine the agreement between the standard pencil and paper pain VAS (pVAS) and a relatively newly designed plastic mechanical (slide-rule) VAS (mVAS) in assessing cervical and lumbar pain intensity in cervical pain vs low back pain (LBP) patients stratified by age (< 65 years of age (yoa) and ¡Ý 65 yoa).
This was a concurrent validity study assessing the agreement between the gold standard pVAS and the experimental mVAS.
A sample size estimate revealed that a minimum of 9 subjects for each of 4 age-complaint subgroups (< 65 yoa) neck pain, ¡Ý 65 yoa neck pain, <65 yoa low back pain, ¡Ý 65 yoa low back pain) would be necessary.
All adults (¡Ý 18 yrs of age) presenting to the Canadian Memorial Chiropractic College¡¯s Herbert K. Lee Outpatient Clinic with low back (LBP) pain or neck pain were considered eligible for the study. Three (3) essentially asymptomatic subjects were also recruited in order to provide a complete spectrum of pain severities.
Pain intensity was measured in centimetres (to nearest one tenth) on the pVAS and in ten units on the mVAS (to the nearest one tenth unit).
The pVAS was administered by including it with either the standard intake forms which all new patients are required to complete, or by presenting it to patients visiting the Clinic for a subsequent treatment. The subject made a visual estimation of his/her pain intensity and marked it on the pVAS accordingly. The response was then measured in centimetres. One of the investigators presented the mVAS to the subject after arrival in the examination room. The mVAS instrument was presented to the subject with instructions as to how to indicate his/her level of present pain intensity. Every attempt was made to ensure that no less than five minutes and no more than 15 minutes elapsed between the completion of the two forms of Visual Analogue Scale. The data were categorized according to the subjects¡¯ ages (¡Ý 65 years of age (yoa) or < 65 yoa) and their areas of complaint (neck pain or low back pain).
Statistical Analysis Strategy:
Intraclass Correlation Coefficient (ICC) analyses were performed to determine the index of agreement between the mVAS and pVAS for each of the age and complaint categories. 95% Confidence Intervals (95% CI) were calculated for each ICC value. A clinically acceptable level of agreement was judged by the investigators to be ICC ¡Ý 0.85; a 95% CI no wider than ¡À 0.25 was considered to provide statistical significance.
The Intraclass Correlation Coefficient (ICC) analysis revealed an ICC of 0.86 with a 95% CI of ¡À 0.25 for the group under 65 yoa with neck pain, and an ICC of 0.87 with a 95% CI of ¡À 0.13 for the group under 65 yoa with low back pain. ICC¡¯s (¡À 95 CI) of 0.60 (¡À 0.64) and 0.93 (¡À 0.2) were calculated for the ¡Ý 65 yoa neck pain group and ¡Ý 65 yoa LBP group, respectively.
The results of this study suggest that for the most part, there is statistically significant and clinically acceptable agreement between the pencil and paper VAS (pVAS) and a mechanical VAS (mVAS). The areas of complaint assessed (neck versus low back), did not appear to affect the level of agreement within each age category; only the older male neck pain and younger female LBP groups, however, yielded clinically unacceptable levels of agreement.
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