Reliability and Validity of Foot Function Index
Thai Version [FFI-TH]
Pitchanart Srimakarat MD1, Araya Jaroenarpornwatana MD2, Siriporn Janchai MD1, Natthiya Tantisiriwat MD2
Affiliation :
1 Department of Rehabilitation Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
2 Department of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital, Thai Red Cross Society, Bangkok, Thailand
and Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
Objective : To assess the reliability and validity of Foot Function Index Thai version [FFI-TH].
Materials and Methods : The cross-sectional descriptive study was conducted in patients with painful foot/ankle problems at
Department of Rehabilitation Medicine, King Chulalongkorn Memorial Hospital, Bangkok, Thailand. Foot Function Index [FFI] is a
self-administered patient-reported outcomes [PRO] measure for evaluating foot/ankle problems. It comprises three domains
including pain, disability, and activity limitation. It was translated into Thai language using internationally recognized translation
standards. Internal consistency reliability coef(cid:976)icients and coef(cid:976)icient of stability were calculated to test for reliability. The average
test-retest interval was 3.90 days. Construct validity was evaluated by the Pain Visual Analogue Score [VAS-pain], the Visual Analogue
Scale Foot and Ankle Thai version [VASFA-TH], and the Medical Outcomes Study [MOS] 36-item short form Thai version [SF36-TH].
Results : Ninety-seven patients were enrolled. Most participants were female (80.47%), with an average age of 45.74 years and an
education level of at least bachelor’s degree (81.40%). The most common diagnoses were plantar fasciitis, ankle sprain, and hallux
valgus. Median time to onset of problem was 5.5 months. Three domains revealed Cronbach’s alpha coef(cid:976)icient values, as follows,
pain subscale (0.94), disability subscale (0.96), and activity limitation subscale (0.72). Intraclass correlation coef(cid:976)icient as 0.92
indicated high stability. Construct validity demonstrated signi(cid:976)icant correlation between the total and subscale of FFI-TH scores
when compared to VAS-pain and SF36-TH for bodily pain, as determined by moderate correlation from Pearson’s correlation
coef(cid:976)icients that ranged from 0.5 to 0.7. Average time to complete the FFI-TH was 4.67 minutes. A higher level of impairment will
correspond with and result in a higher FFI score.
Conclusion : FFI-TH demonstrated good reliability and validity with appropriate completing time. FFI-TH is suitable to be one of
the Thai PRO measures that provide clinical bene(cid:976)it for patients with painful foot/ankle problems.
Keywords : FFI-TH, Foot Function Index, Patient-reported outcome questionnaire, Foot pain, Ankle pain, Validity, Reliability
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