Systemic Lupus Erythematosus
Brief index of lupus damage: A patient-reported measure of damage in systemic lupus erythematosus
To develop and test the Brief Index of Lupus Damage (BILD), an interviewer-administered measure of damage in systemic lupus erythematosus (SLE), for use in epidemiologic studies in which administration of the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI) by trained physicians is not possible or feasible. In addition, we compared the BILD to another recently developed patient-reported measure, the Lupus Damage Index Questionnaire (LDIQ), which was designed as a written survey.
A sample of 81 patients from 2 university-affiliated SLE clinics was used to test the criterion validity of the BILD and the LDIQ. A second sample, the Lupus Outcomes Study (n = 728), was used to ascertain the construct validity of the BILD.
We found good agreement between most BILD items and corresponding SDI items, and moderately high overall Spearman's rank correlations for SDI with BILD (0.64) and with LDIQ (0.54). BILD scores were higher among older individuals, those with longer disease duration, and those with higher mean disease activity in the preceding 4 years. In addition, higher BILD scores were associated with poorer self-rated health and functional status, greater unemployment and work disability, and increased health care utilization.
We developed and performed a preliminary validation study demonstrating content, criterion, and construct validity of a new practical patient-reported instrument of SLE disease damage. Although further studies are needed to examine reliability and to document psychometric properties in other populations, the BILD appears to represent a promising tool for studies of SLE outside the clinical setting.
As survival in patients with systemic lupus erythematosus (SLE) continues to improve, measuring outcomes beyond mortality has become a focus of epidemiologic research. In addition to disease activity, the concept of cumulative damage has emerged as an important outcome in SLE. Damage predicts not only mortality in SLE (1–5), but also a wide range of other outcomes such as physical function (6, 7), health care utilization (8), and disability (9, 10).
Studies examining disease damage in SLE have traditionally relied on a validated physician-assessed measure, the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI) (11). The SDI has been used widely over the last decade, with studies supporting its criterion, discriminant, and construct validity (1–5, 11, 12), as well as its reliability (13). Because the SDI requires a trained physician to complete a 41-item questionnaire, it has largely been used in research conducted in centers with the resources and expertise to study SLE. In recent years, several large community-based studies in SLE using alternative data collection strategies, such as surveys administered by mail or by telephone, have been launched (14, 15). These studies have attempted to broaden clinical research in SLE to include individuals cared for outside of specialty centers. In doing so, a need has arisen to expand the tools available to measure important SLE-related outcomes to include patient-reported measures. A patient-reported measure of SLE disease activity, the Systemic Lupus Activity Questionnaire (SLAQ), has been developed and initially validated for this purpose (16, 17).
Similarly, researchers have recently developed a patient-reported proxy for the SDI, the Lupus Damage Index Questionnaire (LDIQ) (18). The questionnaire has been tested for criterion, content, and construct validity. An international examination of criterion validity in French, Spanish, and Portuguese has also been completed (19). The LDIQ has 56 questions to assess all of the original SDI items and was designed for administration as a written survey. In a concurrent effort, we developed and tested a shorter patient-reported proxy for the SDI meant for interviewer administration in person or on the telephone. The aims of the current study were 3-fold: 1) to develop and test the criterion validity of a new patient-reported damage index, the Brief Index of Lupus Damage (BILD), 2) to examine the construct validity of the BILD in a large, observational cohort of individuals with SLE, and 3) to compare the criterion validity of the BILD to the LDIQ, an instrument that was undergoing validation testing at the time the BILD development was initiated.
PATIENTS AND METHODS
There were 2 sources of data for the study. One sample included 81 patients from 2 university-affiliated SLE clinics and was used to test the criterion validity of the BILD against the SDI. In addition, the clinic-based sample was used to test criterion validity of the newly developed LDIQ. All continuing patients seen between February and September 2009 at one clinic or between December 2010 and February 2011 at the other with a diagnosis of SLE for at least 1 year were eligible for this study.
Recruitment for the clinic-based study took place in the University of California, San Francisco (UCSF) lupus center and at the San Francisco General Hospital lupus clinic, which is staffed by UCSF physicians. Purposive sampling was used to recruit study participants. Patients were initially approached before their regular SLE clinic appointments about participating in a short study of SLE manifestations. Those responding affirmatively were given the BILD questionnaire over the telephone at home prior to their next clinic appointment. Basic demographic questions were included in the interviews, which averaged 10 minutes. Upon returning to the clinic, patients completed the LDIQ in the waiting room prior to their appointment. During that appointment, the rheumatologist completed the SDI. This protocol was designed to ensure that physician queries regarding SDI items occurred last, and therefore did not influence patient responses on either the BILD or the LDIQ. The mean time between the telephone interview and the clinic appointment was 4 months. Of the 109 patients approached, 8 declined to participate, 11 could not be reached by telephone, and 9 did not return to the clinic before the end of the data collection period. Therefore, 81 patients (74%) completed the study. Seven patients were unable to complete the LDIQ, primarily due to time constraints in the clinic.
A sample-size calculation was performed to determine the minimum necessary sample size to assess the criterion validity of BILD. A 0.05 1-sided Fisher's Z test of the null hypothesis that the Spearman's correlation coefficient rho = 0 was estimated to have 80% power to detect an alternative rho = 0.28 when the sample size was 80; moreover, with n = 80, power was estimated at 82% to detect an alternative rho = 0.50 versus the null of rho = 0.25.
The second data source was the Lupus Outcomes Study (LOS), an ongoing cohort of individuals with SLE who are interviewed annually by telephone. Recruitment for the LOS took place in several settings, including university-based rheumatology clinics (25%), community rheumatology offices (11%), and nonclinical sources, including patient support groups and conferences (26%), and other forms of media (38%). All patients had a diagnosis of SLE from a physician, confirmed by a formal review of the medical record to document American College of Rheumatology criteria for SLE (20). Details of the LOS methodology have been published previously (14). The LOS sample (n = 728) was used to test the construct validity of the BILD. The BILD items were included as part of the fifth annual wave of the LOS, which also included validated self-report measures of disease activity, general health status, employment status, work disability, health care utilization, and demographics. Eleven LOS participants who were also part of the clinic sample were excluded, leaving 717 participants for the present independent analysis.
Development of the BILD.
The BILD was designed for administration by telephone interview as part of a longer survey. Investigators modified the existing SDI items to be comprehensible to a lay respondent. The goal was not to replicate the SDI item for item, but to develop a reasonable proxy measure that would distinguish between greater and lesser degrees of SLE damage. Therefore, not all items in the SDI were included because the investigators deemed the manifestation either too rare to be likely to contribute meaningfully to the score (e.g., shrinking lung) or not likely to be interpreted with enough specificity to capture the concept of damage (e.g., alopecia). The initial set of questions was reviewed by 3 patients with SLE for acceptability, feasibility, and understanding; comments were solicited on the clarity and rationale of the directions, the meaning of the items, and the appropriateness of the response choices. Based on this feedback, several questions were revised for clarity. Next, the instrument was included in the LOS interview. During the first month of the survey wave, interviewers recorded all questions from 77 respondents regarding the BILD items. These questions were evaluated by a study rheumatologist (JY), which resulted in several revisions in item prompts and wording. The resulting BILD instrument contained 28 questions that captured information on 26 of the original SDI items (see Supplementary Table, available in the online version of this article at http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2151-4658). The final BILD survey was then administered to the entire LOS sample.
When the BILD was administered to the larger LOS sample, interviewers were instructed to provide clarifications on items if respondents were unclear on their meaning using scripted comments (parenthetical explanations that appear on the instrument). Occasionally, respondents had additional questions that were recorded as free-text notes. A rheumatologist adjudicated these notes when necessary.
Study protocols were approved by the UCSF Committee on Human Research. All participants gave their informed consent to be part of the study.
Clinical sample analysis.
In the clinic sample, we compared the BILD and LDIQ item responses to the corresponding SDI responses. We calculated the item-by-item percent observed agreement (po) with the SDI for each of the 2 proxy measures rather than a kappa statistic, given the low prevalence of individual items. The kappa coefficient is significantly influenced by the prevalence of attributes and its magnitude is difficult to interpret meaningfully if attributes are either very common or very rare, resulting in the so-called kappa paradox with high observed agreement but low kappa (21). The prevalence-adjusted bias-adjusted kappa (PABAK; 2po − 1) has been proposed as a better measure of agreement than kappa when prevalence varies or when the prevalence of each method or instrument differs (22). Like kappa, a PABAK value of −1 indicates perfect disagreement, 0 indicates no agreement, and 1 indicates perfect agreement. We also compared the distributions of the overall SDI, LDIQ, and BILD scores, calculating the Spearman's rank correlation coefficients (rs) for both proxy measures with the SDI.
The LOS was used to assess the construct validity of the BILD and to quantify its acceptability. Because the BILD does not have a normal distribution, we divided the scores from the LOS sample into quartiles to examine its correspondence with demographic, SLE status, general health, and health care utilization measures found in the literature to relate to disease damage measured by the SDI. Sociodemographic measures included age, sex, race/ethnicity (nonwhite versus white), education (high school or less versus some college education or more), household income (at or below 125% of the Federal Poverty Threshold), and employment status. The SLE measures included disease duration and the SLAQ (16), averaged over 4 prior interviews. General health status measures included global health (categorized as excellent/very good/good versus fair/poor), the Medical Outcomes Study Short Form 36 (SF-36) health survey physical and mental component scores, and work disability status. Health care utilization measures included the annual mean number of outpatient medical visits for SLE over the first 5 years of the study, as well as the total number of hospitalizations during that time. Distributions of categorical measures were compared across quartiles of BILD using 1 df chi-square trend tests. Continuous measures were compared using analysis of variance F tests. Finally, to explore the independent association of the sociodemographic measures with BILD, we modeled the BILD score (either top quartile versus not, bottom quartile versus not, and raw score) as a function of age, disease duration, sex, race/ethnicity, and education, using logistic regression.
Both samples were comprised mainly of women and were fairly well-educated (Table 1). The clinic sample, however, was younger than the LOS survey sample, had been diagnosed more recently, and had a larger proportion of racial/ethnic minorities, likely due to recruitment from urban health care settings. Survey sample participants had moderate disease activity levels over the past 4 years and an average SF-36 score of 38, which is typical of a chronically ill population (mean SF-36 score is 50 for general population; higher scores represent better health). Fewer than half the sample was employed and 30% reported work disability.
Table 1. Sample descriptions for clinic and LOS survey samples*
|Female||75 (93)||661 (92)|
|Age at interview, mean ± SD years (range)||35 ± 11 (18–61)||51 ± 12 (22–86)|
|High school education or less||24 (30)||103 (14)|
|Nonwhite||61 (75)||239 (33)|
|Currently employed||NA||324 (45)|
|Poverty-level income||NA||78 (11)|
|Disease duration, mean ± SD years (range)||10 ± 8 (1–44)||17 ± 8 (3–50)|
|Disease activity over 4 years, mean ± SD SLAQ score (range)||–||13 ± 7 (0–37)|
|Self-rated health, fair/poor||–||305 (43)|
|SF-36 physical component score, mean ± SD (range)||–||38 ± 12 (8–69)|
|Unable to work||–||218 (30)|
|Number of hospitalizations over 5 years, mean ± SD (range)||–||2 ± 3 (0–35)|
|Average annual doctor visits for SLE over 5 years, mean ± SD (range)||–||12 ± 10 (0–83)|
The percent agreement between each SDI item and the corresponding BILD and LDIQ items is displayed in Table 2. Of the 26 SDI items assessed in the BILD, 2 items were not reported by any patients: pulmonary fibrosis and osteomyelitis. Of the 42 SDI items assessed in the LDIQ, only chronic peritonitis was not reported. The observed agreement between the BILD items and the SDI ranged from 75–100%, while PABAKs ranged from 0.70–1.00, except for deforming or erosive arthritis (PABAK 0.68) and extensive scarring/panniculum (PABAK 0.51). The observed agreement between the SDI and the LDIQ for only the items retained in the BILD ranged from 77–100% with PABAKs from 0.68–1.00, except for deforming or erosive arthritis (PABAK 0.61), extensive scarring/panniculum (PABAK 0.54), and cognitive impairment (PABAK 0.54). The observed agreement between the SDI and the LDIQ for all LDIQ items ranged from 53–100% with PABAKs from 0.05–1.00, including 7 items with PABAKs from 0.05–0.61; 4 of the 14 items in the LDIQ but not in the BILD had PABAKs in that range. After analysis of the correspondence between the BILD and the SDI, 2 items (erosive arthritis and extensive scarring of the skin) were so commonly reported as to render them uninformative to the BILD score as a whole; their PABAK scores were <0.70, so they were therefore dropped from the subsequent calculation of the BILD score.
Table 2. Item-by-item comparison of the SDI, the LDIQ, and the BILD in a clinic sample of 81 patients*
|Ocular|| || || || || || || |
| Any cataract ever||14 (17)||14 (7)||93||0.85||14 (19)||97||0.95|
| Retinal change or optic atrophy||2 (2)||6 (7)||93||0.85||10 (14)||89||0.78|
|Neuropsychiatric|| || || || || || || |
| Cognitive impairment/major psychosis||6 (7)||4 (5)||88||0.75||17 (23)||77||0.54|
| Seizures requiring therapy ≥6 months||7 (9)||4 (5)||94||0.88||3 (4)||93||0.86|
| Cerebrovascular accident/resection||4 (5)||10 (12)||90||0.80||5 (7)||93||0.86|
| Transverse myelitis||0||1 (1)||99||0.98||12 (16)||84||0.68|
| Cranial/peripheral neuropathy||6 (7)||Omitted|| || ||18 (24)||73||0.46|
|Renal|| || || || || || || |
| End-stage renal disease (dialysis/transplant)||6 (7)||8 (10)||95||0.90||4 (5)||96||0.92|
| Glomerular filtration rate <50%||4 (5)||Omitted|| || ||32 (43)||62||0.24|
| Proteinura >3.5 gm/24 hours||5 (6)||Omitted|| || ||40 (54)||53||0.05|
|Pulmonary|| || || || || || || |
| Hypertension||2 (2)||5 (6)||96||0.93||7 (9)||93||0.86|
| Fibrosis||0||0||100||1.00||5 (7)||93||0.86|
| Shrinking lung||0||Omitted|| || ||1 (1)||99||0.97|
| Pleural fibrosis||1 (1)||Omitted|| || ||4 (5)||96||0.92|
| Infarction/resection||1 (2)||Omitted|| || ||5 (7)||95||0.89|
|Cardiovascular|| || || || || || || |
| Angina/coronary artery bypass||0||2 (2)||98||0.95||3 (4)||96||0.92|
| Myocardial infarction||2 (2)||1 (1)||98||0.95||1 (1)||99||0.97|
| Pericarditis ≥6 months/pericardiectomy||5 (9)||3 (5)||93||0.86||5 (9)||96||0.93|
| Cardiomyopathy||4 (5)||Omitted|| || ||3 (4)||99||0.97|
| Valvular disease||1 (1)||Omitted|| || ||3 (4)||95||0.89|
|Peripheral vascular|| || || || || || || |
| Minor tissue loss (pulp space)||4 (5)||14 (17)||88||0.75||4 (5)||95||0.89|
| Significant tissue loss, ever||0||2 (2)||98||0.95||3 (4)||96||0.92|
| Venous thrombosis with swelling, ulceration, or venous status||8 (10)||10 (12)||88||0.75||5 (7)||88||0.76|
| Claudication, ≥6 months||0||Omitted|| || ||9 (12)||88||0.76|
|Gastrointestinal|| || || || || || || |
| Chronic peritonitis||0||2 (2)||98||0.95||0||100||1.00|
| Stricture or upper gastrointestinal tract surgery||0||1 (1)||99||0.98||6 (8)||92||0.84|
| Infarction/resection bowel, spleen, liver, gall bladder||3 (4)||Omitted|| || ||5 (7)||97||0.95|
| Mesenteric insufficiency||0||Omitted|| || ||Omitted|| || |
| Pancreatic insufficiency||1 (1)||Omitted|| || ||1 (1)||100||1.00|
|Musculoskeletal|| || || || || || || |
| Deforming/erosive arthritis‡||2 (2)||12 (15)||84||0.68||12 (16)||81||0.61|
| Osteoporosis with fracture or vertebral collapse||4 (5)||6 (74)||95||0.90||4 (5)||92||0.84|
| Avascular necrosis||7 (9)||6 (7)||96||0.93||5 (7)||95||0.89|
| Osteomyelitis||0||0||100||1.00||1 (1)||99||0.97|
| Muscle atrophy or weakness||4 (5)||Omitted|| || ||1 (1)||93||0.86|
| Ruptured tendon||0||Omitted|| || ||1 (1)||98||0.96|
|Skin|| || || || || || || |
| Extensive scarring/panniculum‡||8 (10)||28 (35)||75||0.51||21 (28)||77||0.54|
| Skin ulceration (not thrombosis) >6 months||4 (5)||8 (10)||93||0.85||8 (11)||92||0.84|
| Scarring chronic alopecia||5 (6)||Omitted|| || ||13 (18)||80||0.59|
|Premature gonadal failure||1 (2)||13 (16)||85||0.70||6 (8)||91||0.81|
|Diabetes mellitus||4 (5)||7 (9)||90||0.80||6 (8)||95||0.89|
|Malignancy||1 (2)||2 (2)||99||0.98||2 (3)||99||0.97|
Despite differences in the item-by-item comparisons of the SDI and the BILD, the distributions of these 2 scores were similar, while the LDIQ scores were predictably considerably higher. The BILD and SDI had a moderately high rs of 0.64 (P < 0.001). In our sample, the rs of the SDI and the LDIQ was 0.54 (P < 0.001) (Table 3), which is comparable to that reported in the original LDIQ validation paper (rs = 0.48) (18).
Table 3. Distributions and comparisons of 3 systemic lupus erythematosus damage scores in a clinic sample of 81 patients*
|SDI (n = 81)||54 (67)||2||1||0–3||7||–|
|Brief Lupus Damage Index (n = 81)||57 (70)||2||1||0–3||6||0.64 (P < 0.001)|
|Lupus Damage Index Questionnaire (n = 74)‡||64 (86)||4||3||1–5||14||0.54 (P < 0.001)|
The next phase of the study involved administering the BILD to participants in the LOS. The acceptability of the BILD for LOS respondents was very high. Only 4 items had more than 1% of individuals who did not respond (resulting in missing values); these included history of angina or bypass (n = 12), retinal disease (n = 11), peritonitis (n = 10), and interstitial lung disease (n = 9). In the LOS, the median BILD score was 1 with an interquartile range of 0–3 and a maximum score of 6 (data not shown), which is identical to the clinic sample.
In Table 4, we evaluated the construct validity of the BILD by comparing demographic, health status, and health utilization characteristics of the LOS participants to their quartile of the BILD (quartile scores were 0, 1, 2–3, and ≥4 points). As BILD quartiles increased (reflecting greater damage), respondent age increased, as did the percent with incomes below poverty and the percent reporting being unemployed (P < 0.001 for all). No clear relationship was seen by race/ethnicity or sex. Individuals in higher BILD quartiles also had longer disease duration, higher 4-year mean disease activity scores, lower SF-36 physical and mental component scores, and higher percentages with poor self-rated health and work disability (P < 0.001 for all), with each of these demonstrating monotonic relationships. Finally, individuals in the higher BILD quartiles also had more hospitalizations and a greater number of physician visits for SLE over the previous 5 years (P < 0.001).
Table 4. Comparisons of demographic, health status, and health utilization measures, by quartiles of BILD, in the Lupus Outcomes Study survey sample (n = 717)*
|Sociodemographics|| || || || || |
| Age at interview, mean ± SD years||46 ± 12||50 ± 12||52 ± 12||56 ± 12||< 0.001|
| High school education or less||20||28||26||25||0.916|
| Household income below poverty level||12||22||26||41||< 0.001|
| Employed||27||32||32||9||< 0.001|
|SLE status|| || || || || |
| Disease duration, mean ± SD||13 ± 6||16 ± 8||18 ± 9||20 ± 9||< 0.001|
| SLAQ averaged over 4 years, mean ± SD||9 ± 6||11 ± 7||12 ± 7||17 ± 8||< 0.001|
|General health status|| || || || || |
| Fair/poor self-rated health||11||19||33||38||< 0.001|
| SF-36 physical component score, mean ± SD||45 ± 11||41 ± 11||37 ± 11||30 ± 11||< 0.001|
| SF-36 mental component score, mean ± SD||48 ± 10||48 ± 12||48 ± 12||44 ± 14||< 0.001|
| Unable to work||9||20||30||41||< 0.001|
|Health care utilization|| || || || || |
| Hospitalizations over 5 years, mean ± SD||0.5 ± 0.9||0.8 ± 1.4||1.7 ± 3.1||3.4 ± 4.2||< 0.001|
| Average annual doctor visits for SLE over 5 years, mean ± SD||6.9 ± 5.7||8.6 ± 5.8||11.2 ± 8.3||19.2 ± 13.7||< 0.001|
To further examine the relationship between sociodemographic characteristics and damage, we constructed several multivariable models, where the outcome was the BILD score (top quartile versus not, bottom quartile versus not, and raw score), and predictors included age, sex, race/ethnicity, disease duration, and poverty status. All analyses yielded similar conclusions, with disease duration and poverty emerging as significant predictors of damage; no statistically significant effect was seen by race/ethnicity.
Extending scientific research outside the clinical setting in SLE remains a challenging task. The relative rarity and complexity of the disease are barriers for population studies, as are the lack of suitable case findings and disease assessment tools. Although measures of general health such as the SF-36 provide some insight into disease status in epidemiologic studies, more specific tools have the potential to better detect health-related outcome changes. The development and validation of patient-reported instruments hold promise in addressing this gap. In this study, we report our methods for developing and performing an initial validation study of a patient-reported instrument, the BILD, which is designed to assess disease damage. Our findings suggest that the BILD is acceptable to respondents, efficient to administer, and has content, criterion, and construct validity.
We designed the BILD to capture the overall concept of damage in SLE for epidemiologic research. It is important to note that it is not a direct substitute for the SDI, since the BILD omits many items from the SDI that were either not suitable for patient self-report or were not informative because of their frequent reporting by patients. Instead, among a group of patients (rather than in any individual patient), the BILD is able to differentiate between those with high or low degrees of SLE damage. We found good agreement between items in the BILD and the corresponding items in the SDI, and an overall moderately high correlation between the 2 measures (rs = 0.64), suggesting criterion validity. In addition, through both pilot testing and administration of the instrument to more than 700 individuals with SLE, we found that the instrument was acceptable to patients, as evidenced by the very high individual item response rate.
To ascertain construct validity, we compared the patients in the 4 quartiles of BILD scores on measures found in previous literature to relate to disease damage as measured by the SDI. Consistent with studies of the SDI, we found that BILD scores in the LOS were higher among older individuals, those with longer disease duration, and those living below the federal poverty level (9, 23–27). Some previous studies have suggested greater damage among certain racial/ethnic minority groups (23), but many have not, once poverty was accounted for (28–30); we also did not find a statistically significant association between damage and race/ethnicity in our multivariable analyses. As expected, those with a higher mean disease activity score over a 4-year period had higher damage scores (25). Higher BILD scores were also associated with worse self-rated health, a lower SF-36 physical component score, and work disability and employment (6, 9, 10). Finally, individuals with higher BILD scores had significantly greater health care utilization, including a greater number of hospitalizations and physician visits over the last 4 years. This is consistent with health care utilization studies involving the SDI (8, 31).
The LDIQ, a written survey to assess patient-reported damage, was developed concurrently with our effort to develop and test the BILD for telephone or interviewer administration. The LDIQ investigators allowed us to simultaneously test the criterion validity of that instrument in our clinic sample, providing a second US validation for that instrument. We found that both the LDIQ and the BILD correlated acceptably with the SDI (rs = 0.54 for LDIQ, rs = 0.64 for BILD). The correlation of the LDIQ and SDI in our study sample was similar to the published LDIQ criterion validity assessments performed in the US (rs = 0.48). Important differences between the BILD and the LDIQ include the mode of administration (LDIQ is a written survey; BILD is designed for administration by an interviewer in person or on the telephone) and length (LDIQ has 56 items; the final BILD instrument has 26 items). Given 4 large international patient samples, criterion validity testing for the LDIQ has been significantly more extensive; the BILD will require further testing to confirm criterion validity in larger, independent samples. Construct validity testing for the 2 instruments has been comparable in 2 large community-based samples (the National Databank of Rheumatic Diseases for the LDIQ and the LOS for the BILD) (18).
Although the analyses presented here support the content, criterion, and construct validity of the BILD, it is important to note that characterization of the other psychometric properties of the instrument will require further research. For example, we did not assess the reliability of the BILD (either test–retest, or inter-interviewer reliability). Assessment of external validity in an independent sample with different sociodemographic or clinical characteristics should also be performed. The clinic-based sample used to assess criterion validity and the LOS sample differed significantly based on race/ethnicity, disease duration, and age. Theoretically, the BILD could correlate differently among these subgroups with the physician-assessed SDI, and future studies of criterion validity with a larger, more heterogeneous sample should investigate this possibility. Finally, an important strength of the SDI is its association with significant long-term clinical outcomes, such as mortality. It remains to be seen whether either of the 2 newly developed patient-reported measures of disease damage will have similar predictive validity.
In summary, we have developed and performed a preliminary validation study of a new patient-reported instrument of disease damage in SLE. The BILD, which is designed for telephone or interviewer administration, had content, criterion, and construct validity in this study. Although further studies are needed to examine its reliability and to document its psychometric properties in populations with different sociodemographic or clinical characteristics, the BILD appears to represent a promising tool for studies of SLE outside the clinical setting.
All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Yazdany had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study conception and design. Yazdany, Trupin, Gansky, Yelin, Criswell, Katz.
Acquisition of data. Yazdany, Trupin, Dall'era, Yelin, Katz.
Analysis and interpretation of data. Yazdany, Trupin, Gansky, Yelin, Katz.