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Table 4 Results of measurement properties related to: responsiveness and interpretability

From: Evaluation of the measurement properties of the Manchester foot pain and disability index

Measurement property

Research question

Method

Dataset(s)

Results

Interpretation

Responsiveness

Do change scores on the MFPDI relate to change scores on other instruments as expected?

Pearsson Correlation*

Comparator instruments: FFI, NRS, SF12phys, GPEpain and GPEfunction

 

The responsiveness of the MFPDI is moderate; only 1 out of 7 hypotheses was confirmed and the correlation with the GPE question is < 0.2.

Testing 7 a priori defined hypotheses:

1. Correlation change MFPDI-f and FFI-f (R > 0.5)

T0 and measurement after 3 months (NL T3)

1. R 0.31 (p < 0.000)

2. Correlation change MFPDI-f and SF12 phys (R > 0.5)

n = 178

2. R 0.03 (p = 0.747)

3. Correlation change MFPDI-f and GPE-f (R > 0.5)

3. R -0.46 (p < 0.000)

4. R hypothesis 1 > R hypothesis 2.

4. R 0.31 > R 0.03*

5. Correlation change MFPDI-p and FFI-p (R > 0.5)

5. R 0.37 (p < 0.000)

6. Correlation change MFPDI-p and pain NRS (R > 0.5)

6. R 0.42 (p < 0.000)

7. Correlation change MFPDI-p and GPE-p (R > 0.5)

7. R -0.47 (p < 0.000)

*A priori defined hypothesis

Interpretability

What is the Minimal Important change (MIC)?

MIC: smallest cut-off change score (1-sensitivity)+

MIC: NL T0,

The correlation coefficient between the GPE and change score is too low to calculate a MIC (R < 0.5).

The MFPDI is not responsive enough to calculate a MIC.

NL T3

(1-specificity)

n = 178

What is the Smallest Detectable Change (SDC)? And is the MIC higher than the SDC?

SDC

SDC: NL T0 n = 205

SDC:

The SDC for the perception sub-scale is too large; the SDC is equal to the maximum possible score.

Function: 6.1 (min-max score: 0–18)

Pain: 4.4 (0–10)

Perception: 5.8 (0–6)

Is a floor and or ceiling effect present?

Floor/ceiling effect: % of participants who scored the two lowest possible scores (0 or1) per sub-scale.

Floor/ceiling effect: NL T0 n = 205

Floor/ceiling effects:

The perception sub-scale exhibits a large floor effect.

Function: 8.8%

Pain: 7.4%

Perception: 76.5%

  1. *MFPDI-f = MFPDI- function items, FFI-f = FFI- 5pts function items, SF-12 phys = SF12 physical function items, GPE-f = GPE-function question, MFPDI-p = MFPDI- pain items, FFI-p = FFI- 5pts pain items, NRS-p = Pain Numeric Rating Scale, GPE-p = GPE-pain.