Dear Gareth,
Naturally zero pain on the VAS would be great if you can get it. However,
not all patients could achieve or expect this (particularly for
long-standing chronic conditions) and will be happy with just a certain
amount of improvement. The question is how much improvement is needed
before they are happy?
Firstly, the majority of the literature appears to fall into investigating
how much is needed to change on the VAS before the patient first notices
their pain is changing, not how much needs to change before the patient is
happy.
This is generally called a Minimal Clinically Important Difference but it is
probably more appropriate to call it a Minimal Detectable Difference. All
the studies looking at this for the VAS are done in Emergency Departments
and recommend that a patient first notices a change between 9 and 16mm
(Todd, Funk et al. 1996; Kelly 1998; Gallagher, Liebman et al. 2001; Powell,
Kelly et al. 2001; Gallagher, Bijur et al. 2002). This is particularly
helpful for researchers when interpreting their results as they can then
discard any change less than 9mm as an undetectable change and not a change
worthy of recommending the use of the intervention.
The example I gave in an earlier email illustrates this. A mean 0.7mm
change had occurred between two groups but a single patient would not even
notice or care if their pain had changed by 0.7mm.
Secondly, you need to look at how much change occurs before a patient is
happy. Some prefer to call this the Minimal Clinically Worthwhile
Difference. Much less has been written on this but generally a change of 29
to 32mm appears to be needed before a patient reports adequate treatment
(Lee, Stiell et al. 2000; Lee, Hobden et al. 2003; Lock, Carrier et al.
2003).
This is a growing area, and not just for the VAS but across all
patient-based measures. There are problems with the method of determining
such changes (basically there is no gold standard method of measuring
patient pain to compare the VAS results to or ever will be?) but for the
moment this is what we have to go on. Hope that helps and more importantly,
makes sense?
Kind regards,
Joel.
Gallagher, E. J., P. E. Bijur, et al. (2002). “Reliability and validity of a
visual analog scale for acute abdominal pain in the ED.” American Journal of
Emergency Medicine 20(4): 287-290.
Gallagher, E. J., M. Liebman, et al. (2001). “Prospective validation of
clinically important changes in pain severity measured on a visual analog
scale.” Annals of Emergency Medicine 38(6): 633-638.
Kelly, A.-M. (1998). “Does the clinically significant difference in visual
analog scale pain scores vary with gender, age, or cause of pain?” Academic
Emergency Medicine 5(11): 1086-1090.
Lee, J. S., E. Hobden, et al. (2003). “Clinically important change in visual
analog scale after adequate pain control.” Academic Emergency Medicine
10(10): 1128-1130.
Lee, J. S., I. Stiell, et al. (2000). “Clinically meaningful values of the
visual analog scale of pain severity.” Academic Emergency Medicine 7: 550.
Lock, B. G., E. R. Carrier, et al. (2003). “The minimum acceptable reduction
in pain on a visual analog scale.” Annals of Internal Medicine 10(5): 482.
Powell, C. V., A.-M. Kelly, et al. (2001). “Determining the minimum
clinically significant difference in visual analog pain score for children.”
Annals of Emergency Medicine 37(1): 28-31.
Todd, K. H., K. G. Funk, et al. (1996). “Clinical significance of reported
changes in pain severity.” Annals of Emergency Medicine 27(4): 485-489.
-----Original Message-----
From: A group for the academic discussion of current issues in podiatry
[mailto:[log in to unmask]]On Behalf Of Gareth Milne
Sent: Wednesday, 8 September 2004 4:49 PM
To: [log in to unmask]
Subject: Re: BJP Paper and Orthotic Evaluation
Hi Joel,
I would be interested in reading some references on
VAS and how much of a change there needs to be for it
to be improving. We (3 podiatrists) use the VAS quite
a lot to help measure improvement. In the big picture
though, shouldn't we really be aiming for zero on the
VAS for the patient to be improving or improved??
--- Joel Radford <[log in to unmask]> wrote:
> Dear Paul,
>
> Yes, I agree that the patients in the ESWT trial
> have not improved by
> treatment.
>
> However, your statement that the "VAS is a very
> crude method of measuring
> anything" may not be accurate. I'd be interested in
> the references of the
> studies you're referring to.
>
> As far as I know, the VAS has long been accepted as
> reliable and valid
> measure, particularly for pain:
>
> - Revill et al (1976) found in 39 participants high
> correlations between
> measurements of remembered pain (r=0.97 to 0.99).
> - Scott and Huskisson (1976) demonstrated that the
> VAS does not differ
> significantly from a uniform distribution when 100
> patients were assessed
> for pain.
> -And Price et al (1983) demonstrated high between
> session reliability
> (r=0.97) for 50 participants who received pain
> evoked by heat pulses. In
> addition 30 of these participants had chronic back
> pain and were able to
> easily scale the intensity of their pain at its
> minimal (20mm), usual (49mm)
> and maximal levels (72mm) on a 15mm VAS.
> -Also, the frequent use of the VAS in clinical
> trials across most medical
> fields demonstrates its apparent responsiveness to
> change.
>
> If anyone is interested in what change on a visual
> analogue scale is needed
> before a patient can be seen to be improving I could
> provide some references
> for that too.
>
> Kind regards,
>
> Joel.
>
>
>
> Price, D. D., P. A. McGrath, et al. (1983). The
> Validation of Visual
> Analogue Scales as Ratio Scale Measures for Chronic
> and Experimental Pain.
> Pain 17: 45-56.
>
> Revill, S. I., J. O. Robinson, et al. (1976). The
> reliability of a linear
> analogue for evaluating pain. Anaesthesia 31:
> 1191-1198.
>
> Scott, J. and E. C. Huskisson (1976). Graphic
> representation of pain. Pain
> 2: 175-184.
>
>
>
> -----Original Message-----
> From: A group for the academic discussion of current
> issues in podiatry
> [mailto:[log in to unmask]]On Behalf Of Paul
> Conneely
> Sent: Sunday, 5 September 2004 5:56 PM
> To: [log in to unmask]
> Subject: Re: BJP Paper and Orthotic Evaluation
>
>
> Dear All
>
> The VAS is a very crude method of measuring
> anything. Studies regarding
> the reliability and Validity of VAS and thus
> accuracy of the VAS indicate
> that this measuring method is 'crude' at best.
>
> A P value of 0.04 suggests that there is a 4%
> probability that chance is
> involved in the treatment, that is they got better
> of their own accord.
>
> When applying the miniscule changes to the VAS that
> these patients have
> over three month period, one can conclude that they
> have not improved by
> treatment but by time.
>
> Paul Coneely.
>
>
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