Twiss J, Ben-L’amri M, McKenna SP

February 2012Galen Research Ltd.

Comparison of the CAMPHOR and SF-36 for Pulmonary

Hypertension (PH) patients

Introduction

• CAMPHOR and SF-36 both widely used measures in PH• CAMPHOR is the only disease-specific measure for PH• CAMPHOR has been shown to be unidimensional,

reliable, valid and responsive in this patient group (McKenna, 2006; Meads, 2008)

Aims of study

To compare psychometric quality of the CAMPHOR and SF-36

Methodology

• Sample: 65 Australian PH patients• CAMPHOR and SF-36 data available at two

time points• Measures were assessed for:– Floor (% min) and Ceiling (% max) effects

[High % = lack of sensitivity]

– Internal consistency (required minimum=0.70)– Test-retest reliability (required minimum=0.85)– Construct validity by WHO classification

Results – Demographics (n=65)

Gender Male (%) 14 (21.5)

Female (%) 51 (78.5)

AgeMean (SD) 57.2 (14.5)

Range 20.1-87.5

WHO Classification1 (%) 3 (4.6)

2 (%) 18 (27.7)

3 (%) 40 (61.5)

4 (%) 4 (6.2)

Floor and Ceiling effects – SF-36 Time 1

PF RP BP GH VT SF RE MH0%

5%

10%

15%

20%

25%

30%

Floor effect Ceiling effect

Floor and Ceiling effects – CAMPHOR Time 1

Symptoms Activity Limitations QoL0%

5%

10%

15%

20%

25%

30%

Floor effect Ceiling effect

Interpretation of findings

• Three of the eight SF-36 domains had high ceiling effects

• This indicates that domains lack sensitivity in this patient group

• Low levels of floor and ceiling effects found for the CAMPHOR

• CAMPHOR scales were well matched to severity level of the patients

Internal consistency – interpretation of findings

• All domains and scales showed adequate internal consistency

• This indicates that the items were sufficiently inter-related

• However, this is not a sufficient test of reproducibility – crucial for a measure intended to detect change

Test-retest reliabilityMeasure Item Test-retest % explained

variance (r2)SF-36 Physical Functioning .93 86

General Health Perceptions .94 88

Role-Physical .81 66

Bodily Pain .72 52

Vitality .78 61

Social Functioning .76 58

Role-emotional .70 49

Mental Health .75 56

CAMPHOR Symptoms .86 74

Activity Limitations .87 76

Quality of Life .94 88

Unacceptable level of

reliability

Interpreting test-retest data: confidence intervals for the SF-36 and CAMPHOR

Test-retest Time 1 mean SEM* Corresponding CI**

SF-36 Physical Functioning .93 35.3 5.79 29.5 - 41.1

Role-Physical .81 41.9 12.16 29.7 - 54.1

Bodily Pain .72 53.4 13.28 40.1 - 66.7

General Health .94 30.3 4.85 25.5 - 35.1

Vitality .78 38.2 11.16 27.0 - 49.4

Social Functioning .76 62.1 15.24 46.9 - 77.3

Role-emotional .70 67.9 17.09 50.8 - 85.0

Mental Health .75 67.4 8.95 58.5 - 76.4

CAMPHOR Symptoms .86 13.0 2.24 10.8 - 15.2

Activities .87 9.9 2.13 7.8 - 12.0

QoL .94 10.4 1.59 8.8 - 12.0

*SEM = Standard error of measurement; ** Corresponding confidence interval

Interpreting test-retest data– SF-36

• Six of eight domains below 0.85• Large confidence intervals observed• This indicates the domains have high levels of

random measurement error• Such high levels of random measurement

error make the measure unsuitable for clinical trials

Interpreting test-retest data–CAMPHOR

• The CAMPHOR scales had excellent test-retest reliability

• Narrow confidence intervals• Low levels of random measurement error• Changes on CAMPHOR scales are more likely

to be accurate• CAMPHOR more likely to detect real changes

associated with effective interventions

Known-Groups validity – SF-36PFMean (SD)

RPMean (SD)

BPMean (SD)

GHMean (SD)

VTMean (SD)

SFMean (SD)

REMean (SD)

MHMean (SD)

TIME 1WHO Classification

1 & 2 49.5 (21.6)

61.3 (26.9)

60.1 (25.9)

38.9 (18.5)

48.2 (20.5)

75.0 (27.4)

82.9 (19.3)

72.1 (17.1)

3 & 4 27.9 (18.4)

31.4 (22.5)

49.9 (24.3)

25.7 (19.1)

33.0 (24.0)

55.3 (31.1)

59.8 (33.5)

64.9 (18.0)

p .000 .000 .360 .009 .015 .014 .010 .165

TIME 2 WHO Classification

1 & 2 48.5 (23.8)

59.4 (20.7)

61.7 (25.8)

38.3 (20.7)

47.9 (20.9)

72.6 (24.2)

76.2 (23.3)

73.8 (16.7)

3 & 4 28.3 (17.2)

34.2 (27.6)

50.6 (26.4)

26.4 (20.8)

31.4 (19.4)

54.5 (30.3)

63.8 (30.0)

68.0 (19.1)

p .001 .001 .158 .034 .005 .027 .123 .167

Known-Groups validity – CAMPHOR

Symptoms Activity Limitations QoL

TIME 1WHO Classification1 & 2 10.4 (5.3) 7.2 (5.7) 7.3 (6.1)

3 & 4 14.3 (5.9) 11.2 (5.7) 11.9 (6.2)

p 0.012 0.011 0.007

TIME 2 WHO Classification1 & 2 10.1 (5.3) 7.7 (6.2) 7.8 (5.8)

3 & 4 13.6 (6.0) 12.3 (5.5) 12.2 (6.1)

p 0.031 0.003 0.006

Interpreting known-groups validity findings – SF-36• Bodily Pain, Role-Emotional and Mental

Health domains did not distinguish between severity groups

• A measure used for PH patients should be able to distinguish between the relatively large differences between WHO classes

• Raises doubts about ability of SF-36 to distinguish between interventions

Interpreting known-groups validity data – CAMPHOR• All scales were able to distinguish between

WHO classes• The CAMPHOR is sensitive to clinically relevant

information

Previous research showing MID values

Measure Scale Score range MID value

SF-36 Physical functioning 0-100 13

Role-physical 0-100 25

Social functioning 0-100 21

Vitality 0-100 15

CAMPHOR Symptoms 0-25 2

Activity limitations 0-30 2

QoL 0-25 2

Utility 0-1 0.09

Previous research has provided the following MID values for PH patients:

High MID values

Conclusions – SF-36

• The SF-36 performed poorly overall• Only Physical Functioning and General Health

Perception scales had adequate psychometric properties

• It lacks sensitivity and has high levels of measurement error

• Many of scales appear non-relevant to PH patients• Supports other evidence showing SF-36 domains

have large minimal important differences (Gilbert et al, 2009)

Conclusions - CAMPHOR• CAMPHOR scales exhibited excellent psychometric properties • As it is a disease-specific measure the content is highly relevant

to PH patients• Low levels of floor and ceiling effects and high test-retest

reliability show the measure is sensitive and has low levels of random measurement error

• Previous research has shown the CAMPHOR is responsive to treatment-related change (Meads et al., 2008)

• The Activity Limitations scale of the CAMPHOR provides a PH-specific measure of physical functioning and offers a better alternative to the SF-36 Physical Functioning domain and 6 minute walk test

References

McKenna SP, Doughty N, Meads DM, Doward LC & Pepke-Zaba J. The Cambridge Pulmonary Hypertension Outcome Review (CAMPHOR): A measure of health-related quality of life and quality of life for patients with pulmonary hypertension. Quality of Life Research (2006) 15: 103–15.

Meads DM, McKenna SP, Doughty N, Das C, Gin-Sing W, Langley J and Pepke-Zaba J. The responsiveness and validity of the CAMPHOR Utility Index. The European Respiratory Journal (2008) 32: 1513–9.

Gilbert C, Brown MC, Cappelleri JC, Carlsson M, McKenna SP. Estimating a minimally important difference in pulmonary arterial hypertension following treatment with Sildenafil. Chest (2009) 135: 137-42.