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Analyses of Cross-Sectional Data to Link the PEG With the Patient Reported Outcomes Measurement and Information System (PROMIS) Global Physical Health Scale

Open AccessPublished:June 25, 2022DOI:https://doi.org/10.1016/j.jpain.2022.06.006

      Highlights

      • PROMIS global physical health scale and the PEG scale are correlated.
      • Studies that administer the PEG can estimate the PROMIS scale.
      • This link facilitates comparisons among studies using different measures.

      Abstract

      It is challenging to synthesize findings across studies of pain impact. This study develops a link to estimate the Patient-Reported Outcomes Measurement Information System (PROMIS) global health measure from the 3-item Pain intensity, interference with Enjoyment of life, interference with General activity (PEG) scale. The PROMIS and PEG items were administered to 795 adults (average age = 51; 54% female, 79% White). We estimated correlations among the PEG and PROMIS items and conducted factor analysis to identify the best subset of PROMIS items for linking to the PEG. An item response theory graded response model was estimated to link the PEG with the 4-item PROMIS global physical health scale. A categorical single-factor model and a bifactor model provided support for a single dimension for the PEG and PROMIS global physical health items. The product-moment correlation between estimated PROMIS global physical health scale from the PEG and the actual global physical health score was .74. The mean difference between estimated PROMIS global physical health scale score from the PEG and the observed global physical health score was less than a T-score point. This study makes it possible to estimate the average global physical health for group-level comparisons in research that includes the PEG.

      Perspective

      This article describes an empirical link of the PEG to the PROMIS global physical health scale that makes it possible to estimate the average global physical health in studies that include the PEG. This link can facilitate comparisons among studies that have not administered the PEG or the PROMIS global health scale.

      Key words

      Generic self-report health measures are by design intended to be applicable to the general population. Because of the general applicability of these measures across different people, they can be used to estimate relative burden of different conditions and different treatments. Some generic measures focus on specific symptoms such as pain while others assess higher-order concepts such as global physical and mental health. An extensive body of research has been conducted with adults having chronic pain using a wide variety of pain-targeted and global health outcome measures.
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      A protocol for chronic pain outcome measurement enhancement by linking PROMIS-29 scale to legacy measures and improving chronic pain stratification.
      The National Institutes of Health Pain Consortium's Research Task Force on chronic low back pain noted that because of variations in study design and measures used it is “difficult to compare epidemiologic data and studies of similar or competing interventions, replicate findings, pool data from multiple studies, resolve conflicting conclusions, develop multidisciplinary consensus, or even achieve consensus within a discipline regarding interpretation of findings”
      • Deyo RA
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      Report of the NIH Task Force on research standards for chronic low back pain.
      (p. 1250).
      When 2 measures are correlated with one another and define an underlying continuum, they can be empirically linked on a common metric.
      • Dorans NJ.
      Linking scores from multiple health outcome instruments.
      ,
      • Schalet BD
      • Lim S
      • Cella D
      • Choi SW.
      Linking scores with patient-reported health outcome instruments: A validation study and comparison of three linking methods.
      A linkage can be done between 2 global measures. For example, the PROMIS global physical and mental health scores can be estimated from the Veterans RAND 12-item general health survey because they were empirically linked.
      • Schalet BD
      • Rothrock NE
      • Hays RD
      • Kazis LE
      • Cook KF
      • Rutsohn JP
      • Cella D.
      Linking physical and mental health summary scores from the Veterans RAND 12-Item Health Survey (VR-12) to the PROMIS® Global Health scale.
      Or the linkage can be between different measures of the same symptom such as depression.
      • Choi SW
      • Schalet B
      • Cook KF
      • Cella D.
      Establishing a common metric for depressive symptoms: Linking the BDI-II, CES-D, and PHQ-9 to PROMIS depression.
      In addition, generic measures of a specific domain can be linked with disease-targeted measures as was the PROMIS physical function scale with the Functional Assessment of Cancer Therapy.
      • Kaat AJ
      • Schalet BD
      • Rutsohn J
      • Jensen RE
      • Cella D
      Physical function metric over measure: An illustration with the Patient-Reported Outcomes Measurement Information System (PROMIS) and the Functional Assessment of Cancer Therapy (FACT).
      While assessing pain and other specific symptoms is critically important when examining individuals with chronic low back pain and other conditions, information about global health can also be useful for researchers and clinicians. Global health scores for a group of patients with a certain condition can be compared to the general population and to patients with other condition to assess the relative burden of the condition. The Patient-Reported Outcomes Measurement Information System (PROMIS) global health instrument is an outcome measure endorsed by the International Consortium for Health Outcomes Measurement.
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      An international standard set of patient-centered outcome measures after stroke.
      The 10 PROMIS global health items impose limited respondent burden as they can be administered in 2 minutes or less. Support for the reliability and validity of the PROMIS global physical and mental health scales is accumulating.
      • Alcantar J
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      Exploratory factor analysis of PROMIS-29 V1.0, PROMIS global health and the RAND SF-36 from chiropractic responders attending care in a practice-based research network.
      ,
      • Hays RD
      • Bjorner J
      • Revicki DA
      • Spritzer KL
      • Cella D.
      Development of physical and mental health summary scores from the Patient-Reported Outcomes Measurement Information System (PROMIS) global items.
      ,
      • Katzan I
      • Lapin B.
      PROMIS GH (Patient-reported Outcomes Measurement Information System Global Health) scale in stroke: A validation study.
      ,
      • Shim J
      • Hamilton DF.
      Comparative responsiveness of the PROMIS-10 global health and EQ-5D questionnaires in patients undergoing total knee arthroplasty.
      One measure increasingly used to assess pain in outcomes research is the Pain intensity, interference with Enjoyment of life, interference with General activity (PEG), which is a 3-item subset of the Brief Pain Inventory (BPI).
      • Krebs EE
      • Lorenz KA
      • Bair MJ
      • Damush TM
      • Wu J
      • Sutherland JM
      • Asch SM
      • Kroenke K.
      Development and initial validation of the PEG, a three-item scale assessing pain intensity and interference.
      The developers reported internal consistency reliability of .73 and .89 in 2 samples and comparable construct validity to the full BPI.
      • Krebs EE
      • Lorenz KA
      • Bair MJ
      • Damush TM
      • Wu J
      • Sutherland JM
      • Asch SM
      • Kroenke K.
      Development and initial validation of the PEG, a three-item scale assessing pain intensity and interference.
      Prior work documents statistically significant and noteworthy associations between the PEG and some PROMIS measures. In a sample of 300 primary care patients, the PEG correlated .46 to .51 with PROMIS-29 depression, fatigue, sleep disturbance and fatigue scales and .86 with pain interference.
      • Kroenke K
      • Stump TE
      • Kean J
      • Talib TL
      • Haggstrom DA
      • Monahan PO.
      PROMIS 4-item measures and numeric rating scales efficiently assess SPADE symptoms compared with legacy measures.
      But the PEG has not yet been linked to a global health measure.
      This paper describes the development of a linkage from the PEG to the PROMIS global physical health measure using data collected in the development and evaluation of the PROMIS measures.
      • Cella D
      • Choi SW
      • Condon DM
      • Schalet B
      • Hays RD
      • Rothrock NE
      • Yount S
      • Cook KF
      • Gershon RC
      • Amtmann D
      • DeWalt DA
      • Pilkonis PA
      • Stone AA
      • Weinfurt K
      • Reeve BB
      PROMIS® adult health profiles: Efficient short-form meansures of seven health domains.
      ,
      • Hays RD
      • Bjorner J
      • Revicki DA
      • Spritzer KL
      • Cella D.
      Development of physical and mental health summary scores from the Patient-Reported Outcomes Measurement Information System (PROMIS) global items.

      Methods

      Sample

      As part of the PROMIS wave 1 data collection, a subsample of participants responded to every candidate item of a PROMIS measure and all items of one or more ‘‘legacy instruments’’ that measured the same or a similar concept. Individuals who responded to the PROMIS global health scale also completed the PEG. This is a secondary analysis of cross-sectional data collected from 795 adults (54% female) who completed the PEG and PROMIS global health items (Table 1).
      Table 1Characteristic of the Overall Sample (n = 21,133) and those Administered the PEG Items (n = 795)
      VariableOverall SamplePEG Subgroup
      Age means (SD, range)53 (17, 18–100)51 (18, 18–90)
      Female (%)52%54%
      Race
       White (%)82%79%
       Black (%)9%8%
       Other (%)9%13%
      Spanish (%)9%11%
      Education
       < High school (%)2%2%
       High school graduate (%)16%15%
       Some college (%)39%33%
       College degree (%)24%29%
       Advanced degree (%)19%21%
      Marital Status
       Married or living with partner (%)66%64%
       Never married (%)15%18%
       Separated, divorced or widowed (%)19%18%
      Hypertension (%)41%37%
      Arthritis (%)26%22%
      Depression (%)26%22%
      Anxiety (%)18%14%
      Migraines (%)17%14%
      Cancer (%)17%9%
      Asthma (%)16%15%
      Diabetes (%)13%9%
      Chronic obstructive pulmonary disease (%)11%4%
      Angina (%)10%5%
      Coronary artery disease (%)6%3%
      Congestive heart failure (%)5%2%
      Myocardial infarction (%)6%3%
      Liver disease (%)4%2%
      Kidney disease (%)3%2%
      The average age was 51 and the majority were White (79%), had some college or higher education (83%), and were married or living with a partner (64%). The characteristics of the subsample that was administered the PEG were like the overall PROMIS wave 1 sample but had fewer chronic conditions.

      Measures

      PEG. The 3 PEG items are 1) What number best describes your pain on average in the past week? 2) What number best describes how, during the past week, pain has interfered with your enjoyment of life? 3) What number best describes, how, during the past week, pain has interfered with your general activity? PEG response options range from 0 to 10, with 10 indicating the most severe pain. The PEG scale score is the mean of the 3 items and has a possible range of 0 to 10.
      PROMIS Global Health. This set of 10 items includes 4 items used in scoring the global physical health scale, 4 items used in scoring the global mental health scale, a general health item and a general activity item.
      The 4 PROMIS items used in scoring the global physical health scale (PROMIS item names provided within parentheses) are 1) “In general, how would you rate your physical health?” (global03) 2) “To what extent are you able to carry out your everyday physical activities such as walking, climbing stairs, carrying groceries, or moving a chair?” (global06) 3) “How would you rate your pain on average?” (global07) 4) “How would you rate your fatigue on average?” (global08). Three of these 4 PROMIS items are administered with 5 response options and the other item (global07) is administered with a 0 (no pain) to 10 (worst pain imaginable) response scale. Based on the Sheehan Disability Scale and the Flushing Symptom Questionnaire,
      • Norquist JM
      • Watson DJ
      • Yu Q
      • Paolini JF
      • McQuarrie K
      • Santanello NC.
      Validation of a questionnaire to assess niacin-induced cutaneous flushing.
      the latter item is recoded to 5 categories (5 = no pain; 4 = 1–3; 3 = 4-6; 2 = 7–9; 1 = worse pain imaginable) before scoring the global physical health scale. All 4 items are coded so a higher score represents better global physical health.
      The 4 PROMIS global mental health items are 1) “In general, would you say your quality of life is” (global02) 2) “In general, how would you rate your mental health, including your mood and your ability to think?” (global04) 3) “In general, how would you rate your satisfaction with your social activities and relationships?” (global05) 4) “How often have you been bothered by emotional problems such as feeling anxious, depressed or irritable?” (global10). All 4 of these PROMIS items are administered with 5 response options and coded so a higher score represents better global mental health. Internal consistency reliability of the 4-item global physical health and mental health scales were .81 and .86, respectively.
      • Hays RD
      • Schalet BD
      • Spritzer KL
      • Cella D.
      Two-item PROMIS global physical and mental health scales.
      The global physical and mental health scale scores are estimated using an item-response theory graded response model and transformed to have a mean of 50 and SD of 10 in the U.S. general population.
      • Hays RD
      • Bjorner J
      • Revicki DA
      • Spritzer KL
      • Cella D.
      Development of physical and mental health summary scores from the Patient-Reported Outcomes Measurement Information System (PROMIS) global items.
      Two of the PROMIS global items are not used in scoring the global physical and mental health scales:1) “In general, would you say your health is” (global01); and 2) “In general, please rate how well you carry out your usual social activities and roles. This includes activity at home, at work, and in your community, and responsibilities as a parent, child, spouse, employee, friend, etc.” (global09). Global01 has been administered on several nationally representative health surveys and can be used to estimate the global physical health scale.
      • Hays RD
      • Spritzer KL
      • Thompson WW
      • Cella D.
      U.S. general population estimate for “excellent” to “poor” self-rated health item.

      Analysis Plan

      We estimate means for the PEG score and the PROMIS global physical and mental health scale scores for descriptive purposes. We also report correlations between the PEG scale and the PROMIS global physical health and mental health scales. To identify the subset of PROMIS global health items best suited for linking to the PEG, we begin by estimating product-moment correlations among the 3 PEG and 10 PROMIS global health items and conducting an exploratory factor analysis. Based on the correlations and the exploratory factor analysis, we evaluate a single-factor categorical confirmatory factor analytic model for the PEG items and the subset of PROMIS global health items identified in the above analyses to be most strongly associated with the PEG items. Because Mplus software only allows up to 10 categories per item, we collapsed responses of 9 and 10 (worse pain) into a single category for this analysis. We evaluate fit with the comparative fit index (CFI), the standardized root mean squared residual (SRMR) and the root mean square error of approximation (RMSEA). Good model fit is indicated by a CFI of about .95 or above, a SRMR of about .08 or less, and an RMSEA of about .06 or less.
      • Hu LT
      • Bentler PM.
      Cutoff criteria for fit indexes in covariance structure analysis: Conventional criteria versus new alternatives.
      In addition, we estimate a bifactor model to obtain an indication of general factor saturation (omega hierarchical, ωh) that represents the percent of variance in unit-weighted total scores attributed to individual differences on the general factor. Values>= .80 are suggestive of essential unidimensionality.
      • Rodriguez A
      • Reise SP
      • Haviland MG.
      Applying bifactor statistical indices in the evaluation of psychological measures.
      Next, we fit an item-response theory graded response model
      • Samejima F.
      Graded response model.
      for the PEG items and the PROMIS global physical health items (the PROMIS global health items identified in the above analyses to be most strongly associated with the PEG items) using a single group design with common-item equating.
      • Kolen MJ
      • Brennan RL.
      Test Equating, Scaling, and Linking: Methods and Practices.
      To do this, items are calibrated in a single run with PROMIS item parameters fixed at their previously estimated values and the PEG item parameters freely estimated.
      • Kim S.
      A comparative study of IRT fixed parameter calibration methods.
      PEG items were reversed for this calibration so that a higher score indicate less pain This fixed item calibration of PROMIS global physical health items yields PEG item parameters on the PROMIS metric. We use the polytomous version of the Lord and Wingersky
      • Lord FM
      • Wingersky MS.
      Comparison of IRT true-score and equipercentile observed score" equatings".
      algorithm that computes the probability of each successive response recursively based on previously computed likelihoods
      • Thissen D
      • Pommerich M
      • Billeaud K
      • Williams VS
      Item response theory for scores on tests including polytomous items with ordered responses.
      to map the PEG scale score to the PROMIS global physical health scale. Finally, we estimate the product-moment correlation of the linked PEG scores to actual PROMIS global physical health scores and report the mean and standard deviation of the difference.
      Analyses were conducted using SAS,
      SAS® 9.4 TS Level 1M6.
      Mplus,
      • Muthén L
      • Muthén B.
      Mplus User's Guide.
      R,

      R Core Team. R: A language and environment for statistical computing. 2018. Available at: http://www.r-project.org.

      and PROSetta Stone
      • Choi SW
      • Lim S
      • Schalet BD
      • Kaat AJ
      • Cella D.
      PROsetta: An R package for linking patient-reported outcome measures.
      software: https://www.prosettastone.org.

      Results

      The mean PEG scale score in our sample was 1.82 (SD = 2.18; range: 0–10), much lower than the mean of 6.1 found in a study of 500 adults with musculoskeletal pain.
      • Krebs EE
      • Lorenz KA
      • Bair MJ
      • Damush TM
      • Wu J
      • Sutherland JM
      • Asch SM
      • Kroenke K.
      Development and initial validation of the PEG, a three-item scale assessing pain intensity and interference.
      The PROMIS global physical health score was equal to that of the U.S. general population mean: 50.14 (SD = 8.41; range: 22–67); as was the PROMIS global mental health score of 49.97 (SD = 8.46). Internal consistency reliability of the PROMIS global physical health and PEG scales were .77 and .91, respectively.
      Correlations among the PEG items and PROMIS global health items (Table 2) ranged from .29 (Global05 and PEG1) to .77 (Global07 and PEG1). We provide the correlations for the 2 PROMIS global health items not used in scoring the global physical and mental health scales (global01 and global09) for completeness, but we do not include them in subsequent analyses because they are redundant with the items used in the scales (ie, locally dependent). For example, global01 correlated .90 with global03.
      Table 2Product-Moment Correlations Among 13 Items
      12345961087PEG1PEG2
      2.69
      3.90.70
      4.50.64.51
      5.49.68.51.68
      9.63.67.63.61.64
      6.58.50.58.34.35.58
      10.34.48.35.66.56.50.26
      8.53.50.53.48.44.60.48.48
      7.47.41.47.32.31.46.52.30.48
      PEG1-.47-.42-.45-.32-.29-.45-.54-.28-.46-.77
      PEG2-.46-.47-.48-.41-.38-.50-.55-.39-.48-.62.72
      PEG3-.47-.47-.46-.38-.30-.51-.63-.32-.48-.68.76.84
      1 = Global01: In general would you way your health is…
      2 = Global02: In general, would you say your quality of life is…
      3 = Global03: In general, how would you rate your physical health?
      4 = Global04: In general, how would you rate your mental health?
      5 = Global05: In general, how would you rate your satisfaction with social activities and relationships?
      6 = Global06: To what extent are you able to carry out your everyday physical activities?
      7 = Global07: How would you rate your pain on average? (Note that the 0-10 response scale is recoded to 5 categories: 0 (no pain) -> 5; 1-3 -> 4; 4-6 -> 3; 7-9 -> 2; 10 (worst pain imaginable)-> 1.
      8 = Global08: How would you rate your fatigue on average?
      9 = Global09: In general, please rate how well you carry out your usual social activities and roles?
      10 = Global10: How often have you been bothered by emotional problems?
      PEG1: What number best describes your pain on average in the past week?
      PEG2: What number best describes how, during the past week, pain has interfered with your enjoyment of life?
      PEG3: What number best describes how, during the past week, pain has interfered with your general activity?
      Note: PROMIS global physical health items are global03, global06, global07, and global08.

      Factor Analysis

      An exploratory factor analysis was conducted on the 3 PEG items and 8 PROMIS global health items used in scoring the 4-item global physical health scale and the 4-item global mental health scale. Two principal components eigenvalues exceeded 1 (Guttman's weakest lower bound): the first 3 eigenvalues were 5.67, 1.67 and .83. A scree plot of eigenvalues from a common factor analysis with squared multiple correlations as communality estimates suggested 2 factors (Fig 1). Next, we estimated a principal factor analysis Promax rotated 2-factor solution with squared multiple correlations as prior communality estimates (Table 3). The 3 PEG items did not load on the mental health factor but loaded on the global physical health factor with standardized factor pattern loadings ranging from .78 to .90. Hence, we limit subsequent analyses to the PEG and the 4 global physical health items.
      Figure 1
      Figure 1Scree plot of common factor analysis eigenvalues from common factor analysis with squared multiple correlations as communality estimates.
      Table 3PROMAX Rotated Two-Factor Pattern (Loadings > = .30)
      ItemPhysical HealthMental Health
      PEG3-.90
      PEG1-.88
      Global07.80
      PEG2-.78
      Global06.66
      Global03.30.50
      Global08.32.42
      Global04.82
      Gloabl05.79
      Global02.69
      Global10.69
      Global02: In general, would you say your quality of life is…
      Global03: In general, how would you rate your physical health?
      Global04: In general, how would you rate your mental health?
      Global05: In general, how would you rate your satisfaction with social activities and relationships?
      Global06: To what extent are you able to carry out your everyday physical activities?
      Global07: How would you rate your pain on average?
      Global08: How would you rate your fatigue on average?
      Global10: How often have you been bothered by emotional problems?
      PEG1: What number best describes your pain on average in the past week?
      PEG2: What number best describes how, during the past week, pain has interfered with your enjoyment of life?
      PEG3: What number best describes how, during the past week, pain has interfered with your general activity?
      Note: Estimated correlation = 0.53 between physical and mental health.
      A 1-factor categorical confirmatory model for the PEG items and the 4 global physical health items fit the data well according to 2 indices of practical fit (CFI = .981; SRMR = .037) and the RMSEA was = .159. Standardized factor loadings ranged from .64 to .94. All residual correlations were less than .18. The bifactor model provided support for essential unidimensionality with ωh of .80 (explained common variance = .74), RMSEA = .042, and standardized factor loadings on the general factor ranging from .51 to .89. All loadings on the general factor easily exceeded the corresponding loadings on the group factors.

      Linking

      The correlation of the PEG scale was -.77 (n = 790) with the PROMIS global physical health scale and -.47 (n = 791) with the PROMIS global mental health scale. The correlation between the PEG scale and the PROMIS global physical health scale adjusted for unreliability was .92.
      Table 4 gives the graded response model item parameters from the combined PEG and PROMIS global physical health concurrent calibration. The PEG had larger slopes than the PROMIS global physical health items, indicating that the PEG items more strongly represented the common factor defined by the 7 items. The number of thresholds is one less than the number of response categories for each item. The thresholds indicate that 3 of the PROMIS items (global03 global07, global08) represented the positive range of physical health (1 SD and higher) better than did the PEG items. That is, the PEG item thresholds top out at between -.0251 and .6468.
      Table 4Item Parameters for Global Physical Health (Fixed) and PEG (Estimated)
      Global03Global06Global07Global08PEG1PEG2PEG3
      Slope2.22572.88091.67991.83193.43544.51805.6266
      Threshold 1-2.3068-3.0148-4.1331-3.4747-3.3014-2.1862-2.3795
      Threshold 2-1.0357-1.9551-1.9869-2.0584-2.6493-1.8582-2.0505
      Threshold 3.1876-1.1949-.8116-.4829-2.2348-1.6345-1.6988
      Threshold 41.4917-.5224.92271.1009-1.8155-1.3604-1.4124
      Threshold 5-1.4190-1.2225-1.1787
      Threshold 6-1.0226-1.0634-.9921
      Threshold 7-.7234-.9009-.8175
      Threshold 8-.2984-.6993-.5919
      Threshold 9.0856-.3913-.3137
      Threshold 10.6468-0.0251-0.0081
      Global03: In general, how would you rate your physical health?
      Global06: To what extent are you able to carry out your everyday physical activities?
      Global07: How would you rate your pain on average?
      Global08: How would you rate your fatigue on average?
      PEG1: What number best describes your pain on average in the past week?
      PEG2: What number best describes how, during the past week, pain has interfered with your enjoyment of life?
      PEG3: What number best describes how, during the past week, pain has interfered with your general activity?
      Note: For the item calibration shown here, PEG items were reversed scored so that a higher score represents less pain and interference.
      Table 5 presents the crosswalk from the mean and summed PEG scores (scored in the usual direction, with a higher score representing more pain) to PROMIS global physical health T-scores. For example, a PEG score of 0 (lowest level of pain) is mapped to a PROMIS global physical health score of 61.6 while a PEG mean score of 10 (summed score of 30; most pain) is associated with a PROMIS global physical health score of 20.7. A PEG mean score of 1 (summed score of 3) is consistent with PROMIS global physical health scores near the U.S. general population mean of 50.
      Table 5Estimated PROMIS Global Physical Health Score From PEG Score
      PEG Mean ScorePEG Sum ScorePROMIS Global Physical HealthStandard Error
      0061.65.8
      1/3155.03.4
      2/3252.53.0
      1350.72.8
      4/3449.12.6
      5/3547.92.5
      2646.82.4
      7/3745.82.3
      8/3844.92.3
      9/3944.12.3
      10/31043.32.2
      11/31142.52.2
      141241.82.2
      13/31341.02.2
      14/31440.32.2
      51539.62.2
      16/31638.92.2
      17/31738.22.2
      61837.42.2
      19/31936.62.2
      20/32035.82.2
      72134.92.2
      22/32234.02.2
      23/32333.02.3
      82432.02.3
      25/32530.82.3
      26/32629.52.4
      92728.02.6
      28/32826.22.8
      29/32924.03.2
      103020.74.1
      Note: Estimated using PROSetta Stone software.
      The product-moment correlation between the estimated PROMIS global physical health scale based on the PEG link and the actual PROMIS global physical health scores was .74. The mean for the estimated PROMIS global physical health score (ie, linked score from the PEG) was less than a T-score point (.48) different from the actual PROMIS global physical health score (50.62 vs 50.14) and the standard deviation of the difference was 6.20.

      Discussion

      This study provides a crosswalk that allows the PROMIS global physical health scale to be estimated from the PEG. In this study, the correlation between estimated PROMIS global health linked scores based on PEG items and actual scores (r = .74) exceeded the correlation reported by Schalet et al.
      • Schalet BD
      • Rothrock NE
      • Hays RD
      • Kazis LE
      • Cook KF
      • Rutsohn JP
      • Cella D.
      Linking physical and mental health summary scores from the Veterans RAND 12-Item Health Survey (VR-12) to the PROMIS® Global Health scale.
      between the PROMIS global physical health scale and the Veterans RAND-12 physical component summary score (r = 0.69). Those authors suggested that the size of the correlation could be due to the breadth of the construct of global physical health. In the current study, the mean estimated PROMIS global physical health score was less than a T-score point different from the actual PROMIS global physical health score. This indicates that the mean PROMIS global physical health scale can be accurately estimated from the PEG.
      The link between the PEG and the PROMIS global physical health scales is useful for studies where the PEG has been administered but a global health measure has not. In these studies, global physical health can be estimated to provide information about how the sample compares to the U.S. general population and other subgroups. For example, the mean PEG scale score of 6.1 in Study 1 of the Krebs et al
      • Krebs EE
      • Lorenz KA
      • Bair MJ
      • Damush TM
      • Wu J
      • Sutherland JM
      • Asch SM
      • Kroenke K.
      Development and initial validation of the PEG, a three-item scale assessing pain intensity and interference.
      article corresponds to a PROMIS global physical health score of about 37 (worse than the overall U.S. general population mean). While it is preferable to administer the PROMIS global health measure directly, there is often competing needs in research and clinical practice as well as concerns about response burden.
      It is important to note that there is more error when estimating scores from a link than when the scores are directly measured. That is, PROMIS physical health estimated from the PEG linked scores is less accurate than PROMIS physical health scale scored directly from the PROMIS items. In addition, we recommend that the estimated PROMIS global physical health score only be used for group-level comparisons because the error in estimating individual PROMIS global physical health scores is much higher. Further, the association between linked and actual scores may vary by characteristics of the population. Thus, it is always better to have administered and scored the PROMIS global physical health items directly. But when that is not possible, estimating the PROMIS global physical health scale provides useful comparative information.
      The current study adds to existing linkages of PROMIS measures with other measures. Investigators who have administered the PEG can estimate the PROMIS global physical health scale using the link provided in Table 5. Future research is needed to evaluate how well the link from the PEG scale to the PROMIS global physical health scale generalizes to other samples and settings. It may also be valuable to compare the link developed here with other linking methods.
      • Schalet BD
      • Lim S
      • Cella D
      • Choi SW.
      Linking scores with patient-reported health outcome instruments: A validation study and comparison of three linking methods.
      But, it was noted that “when the dis-attenuated correlation between instruments is .90 or higher, the results of each method are expected to converge and the differences among them will probably be inconsequential at the group level. In this circumstance, unidimensional item response theory linking provides the benefit of creating a bi-directional link, as well as simplicity”
      • Schalet BD
      • Lim S
      • Cella D
      • Choi SW.
      Linking scores with patient-reported health outcome instruments: A validation study and comparison of three linking methods.
      (p. 740). In this study, the correlation between the PEG scale and the PROMIS global physical health scale adjusted for unreliability was .92.
      Using data from 3 clinical trials, Chen et al
      • Chen CX
      • Kroenke K
      • Stump T
      • Kean J
      • Krebs EE
      • Bair MJ
      • Damush T
      • Monahan PO.
      Comparative responsiveness of the PROMIS pain interference short forms with legacy pain measures: Results from three randomized clinical trials.
      reported similar responsiveness for the PEG and PROMIS-29 pain interference short forms. Kean et al
      • Kean J
      • Monahan PO
      • Kroenke K
      • Wu J
      • Yu Z
      • Stump TE
      • Krebs EE.
      Comparative responsiveness of the PROMIS Pain Interference short forms, Brief Pain Inventory, PEG, and SF-36 Bodily Pain subscale.
      found that the PEG was more sensitive to change over 3 months than was the PROMIS-29 pain interference scale (effect sizes of .35 and .14, respectively) in a randomized clinical effectiveness trial of 250 adults receiving telecare management of their moderate to severe and persistent musculoskeletal pain. Further evaluations of the sensitivity to change of the PEG compared to global and other pain-targeted measures will be useful.

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