Minimal Important Difference (MID) of two commonly used outcome measures for foot problems.
BACKGROUND
The Visual Analogue Scale (VAS) and the Foot Health Status Questionnaire (FHSQ) are two commonly used outcome measures for evaluating foot health. This study aimed to calculate the Minimal Important Difference (MID) of the VAS and the FHSQ.


METHODS
184 participants with plantar heel pain were recruited from the general public to take part in two randomised trials (92 participants in each trial) that studied the effectiveness of two conservative interventions for plantar heel pain. Data from these participants were used to calculate the MIDs of the VAS and the FHSQ. An anchor-based method was used to calculate the MIDs. Two distinct types of pain were investigated for the VAS: average pain and first-step pain. All four domains of the FHSQ were investigated: foot pain, foot function, footwear and general foot health.


RESULTS
The MID for the VAS using the anchor-based approach was -8 mm (95% CI: -12 to -4) for average pain and -19 mm (95% CI: -25 to -13) for first-step pain on the 100 mm VAS. The MID for the FHSQ was 13 points (95% CI: 6 to 19) for pain and 7 points (95% CI: 1 to 13) for function. The MID for the footwear domain of the FHSQ was -2 points (95% CI: -8 to 4) and 0 points (95% CI: -7 to 6) for the general foot health domain of the FHSQ.


CONCLUSIONS
The results of this study provide additional evidence for MID values of the VAS and the FHSQ for plantar heel pain. This is important for clinicians and researchers as it provides a greater understanding of how much improvement is required by a patient before a minimal, worthwhile change is experienced. The calculated MIDs will also assist researchers with prospective sample size calculations.
Landorf
Karl B
KB
Department of Podiatry, Faculty of Health Sciences, La Trobe University, Bundoora, Victoria, 3086, Australia. k.landorf@latrobe.edu.au.
Radford
Joel A
JA
Hudson
Susie
S
BMC Musculoskelet Disord. 2007 Apr 19;8:36
17442119
Ann Emerg Med. 1996 Apr;27(4):485-9
8604867
Emerg Med J. 2001 May;18(3):205-7
11354213
Acad Emerg Med. 1998 Nov;5(11):1086-90
9835471
J Orthop Sports Phys Ther. 2007 Feb;37(2):72-84
17366962
J Am Podiatr Med Assoc. 1998 Sep;88(9):419-28
9770933
Value Health. 2002 Jul-Aug;5(4):372-81
12102699
Health Serv Res. 2005 Apr;40(2):593-7
15762909
BMJ. 2001 Jun 2;322(7298):1357-60
11387189
J Clin Epidemiol. 2008 Feb;61(2):102-9
18177782
Foot Ankle Int. 2002 Jun;23(6):538-46
12095123
Pain. 1976 Jun;2(2):175-84
1026900
Musculoskeletal Care. 2006 Dec;4(4):187-203
17117444
Anaesthesia. 1976 Nov;31(9):1191-8
1015603
Control Clin Trials. 1989 Dec;10(4):407-15
2691207
BMC Musculoskelet Disord. 2006 Aug 09;7:64
16895612