Statistical inference by confidence intervals: issues of interpretation and utilization.
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This article examines the role of the confidence interval (CI) in statistical inference and its advantages over conventional hypothesis testing, particularly when data are applied in the context of clinical practice. A CI provides a range of population values with which a sample statistic is consistent at a given level of confidence (usually 95%). Conventional hypothesis testing serves to either reject or retain a null hypothesis. A CI, while also functioning as a hypothesis test, provides additional information on the variability of an observed sample statistic (ie, its precision) and on its probable relationship to the value of this statistic in the population from which the sample was drawn (ie, its accuracy). Thus, the CI focuses attention on the magnitude and the probability of a treatment or other effect. It thereby assists in determining the clinical usefulness and importance of, as well as the statistical significance of, findings. The CI is appropriate for both parametric and nonparametric analyses and for both individual studies and aggregated data in meta-analyses. It is recommended that, when inferential statistical analysis is performed, CIs should accompany point estimates and conventional hypothesis tests wherever possible. (+info)
Determinants of WOMAC function, pain and stiffness scores: evidence for the role of low back pain, symptom counts, fatigue and depression in osteoarthritis, rheumatoid arthritis and fibromyalgia.
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OBJECTIVES: The Western Ontario MacMaster (WOMAC) is a validated instrument designed specifically for the assessment of lower extremity pain and function in osteoarthritis (OA) of the knee or hip. In the clinic, however, we have noted that OA patients frequently have other musculoskeletal and non-musculoskeletal problems that might contribute to the total level of pain and functional abnormality that is measured by the WOMAC. In this report, we investigated back pain and non-articular factors that might explain WOMAC scores in patients with OA, rheumatoid arthritis (RA) and fibromyalgia (FM) in order to understand the specificity of this instrument. METHODS: RA, OA and FM patients participating in long-term outcomes studies completed the WOMAC and were assessed for low back pain, fatigue, depression and rheumatic disease symptoms by mailed questionnaires. RESULTS: Regardless of diagnosis, WOMAC functional and pain scores were very much higher (abnormal) among those complaining of back pain. On average, WOMAC scores for back pain (+) patients exceeded those of back pain (-) patients by approximately 65%,, and 52% of OA patients reported back pain. In regression analyses, study symptom variables explained 42, 44 and 38% of the variance in WOMAC function, pain and stiffness scores, respectively. In the subset of OA patients, radiographic scores added little to the explained variance. The strongest predictor of WOMAC abnormality in bivariate and multivariate analyses was the fatigue score, with correlations of 0.58, 0.60 and 0.53 with WOMAC function, pain and stiffness, respectively. The WOMAC performed well in RA and FM, and correlated strongly with the Health Assessment Questionnaire (HAQ) disability scale and a visual analogue scale (VAS) pain scale. CONCLUSION: The WOMAC captures more than just knee or hip pain and dysfunction, and is clearly influenced by the presence of fatigue, symptom counts, depression and low back pain. WOMAC scores also appear to reflect psychological and constitutional status. These observations suggest the need for care in interpreting WOMAC scores as just a measure of function, pain or stiffness, and indicate the considerable importance of psychological factors in rheumatic disease and rheumatic disease assessments. (+info)
The association between tender points, psychological distress, and adverse childhood experiences: a community-based study.
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OBJECTIVE: To examine the hypothesis that characteristics of somatization and illness behavior, and their childhood antecedents, are associated with the presence of multiple tender points. METHODS: Two hundred eighty-nine subjects who had demonstrated psychological distress (General Health Questionnaire score > or =2) had a tender point examination and in-depth psychological evaluation. In addition, subjects were interviewed about a number of adverse childhood experiences. The 99 subjects with 5 or more tender points were compared with the remaining 190 subjects. RESULTS: A high tender point count (> or =5) was associated with low levels of self-care (odds ratio [OR] 2.4, 95% confidence interval [95% CI] 1.1-5.0), reports of a greater number of somatic symptoms (OR 2.2, 95% CI 1.0-4.9), high levels of fatigue (OR 3.3, 95% CI 1.7-6.3), and a pattern of illness behavior characterized by increased medical care usage (OR 4.2, 95% CI 2.1-8.4). Those with high tender point counts were substantially more likely to report adverse childhood experiences, including loss of parents (OR 2.1, 95% CI 1.1-3.9) and abuse (OR 6.9, 95% CI 2.0-24.6). These results were not explained by the presence of chronic pain. CONCLUSION: These data add further weight to the hypothesis that tender points, as part of the fibromyalgia syndrome, are strongly associated with specific components of psychological distress as well as characteristics of somatization and its antecedents. It is possible that these features contribute to the development of the syndrome of fibromyalgia. (+info)
Rasch analysis of the Western Ontario MacMaster questionnaire (WOMAC) in 2205 patients with osteoarthritis, rheumatoid arthritis, and fibromyalgia.
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OBJECTIVE: Advances in health measurement have led to the application of Rasch Item Response Theory (IRT) analysis (Rasch analysis) to evaluate instruments measuring health status and quality of life of patients, including the Health Assessment Questionnaire and SF-36. This study investigated the extent to which the Western Ontario MacMaster osteoarthritis questionnaire (WOMAC) satisfies the Rasch model, particularly in respect to unidimensionality, item separation, and linearity. METHODS: The study included a total of 2205 patients, 1013 with rheumatoid arthritis (RA), 655 with osteoarthritis of the knee or hip (OA), and 537 with fibromyalgia. All patients completed the WOMAC as part of a longitudinal study of rheumatic disease outcomes. To examine whether the WOMAC pain and function scales each fits the Rasch model, the Winsteps program was used to assess item difficulty, scale unidimensionality, item separation, and linearity. RESULTS: Although the WOMAC worked best in OA, regardless of disorder, both the pain and function scales were unidimensional, had adequate item separation, and had a long range (25-150) of linearity in the function scale. Several functional items, however, had a high information weight fit (INFIT) statistic, indicating poor fit to the model. These items included "getting in and out of the bath" and "going down stairs." CONCLUSION: The WOMAC generally satisfies the requirements of Rasch item response theory across all disorders studied, and is an appropriate measure of lower body function in OA, RA and fibromyalgia. Although some individual items do not fit well, it is not likely that removing such items would result in more than overall minimal differences, and it will be difficult to remove traces of multidimensionality while keeping the central constructs of progressive lower body musculoskeletal abnormality intact. In addition, it is possible that a "purer", still more unidimensional instrument would be less useful in clinical trials and epidemiological studies by restricting the range of the scale. (+info)
Periodic breathing during sleep in patients affected by fibromyalgia syndrome.
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Seventeen patients affected by fibromyalgia syndrome (FMS) (16 females and one male) and 17 matched healthy subjects underwent formal polysomnography, a sleep questionnaire and lung function tests. FMS patients slept significantly less efficiently than the healthy controls (p<0.01), had a higher proportion of stage 1 sleep (mean+/-SD, 21+/-6% versus 11+/-4%; p<0.001), less slow wave sleep (p<0.01) and twice as many arousals per hour of sleep (p<0.001). The respiratory pattern of FMS patients showed a high occurrence of periodic breathing (PB) (15+/-8% of total sleep time) in 15/17 patients, versus 2/17 control subjects. The short length of apnoeas and hypopnoeas did not affect the apnoea/hypopnoea index (5.1+/-3.5 versus 3.2+/-1.6; NS), but FMS patients had a greater number of desaturations per hour of sleep (8+/-5 versus 3+/-3; p<0.01). Pulmonary volumes did not differ between the two groups, but FMS patients had a lower transfer factor of the lung for carbon monoxide (TL,CO (5.8+1 versus 7.7+1 mmol x min(-1) x kPa(-1); p=0.001). PB occurrence correlated with TL,CO (r=-0.62; p=0.01), number of desaturations (r=0.76, p=0.001) and carbon dioxide tension in arterial blood (Pa,CO2) (r=-0.50; p=0.05). Stepwise multiple linear regression analysis showed desaturation frequency (p=0.0001) and TL,CO (p=0.029) to be the best predictors of PB percentage (R2 0.73; p=0.0001). Patients complaining of daytime hypersomnolence had a higher number of tender points, about twice as many arousals per hour and a lower sleep efficiency than patients who did not report this symptom. TL,CO was more impaired and the occurrence of PB was higher. The occurrence of periodic breathing in fibromyalgia syndrome patients, which was previously unreported, and is shown to be linked to a reduction of transfer factor of the lung for carbon monoxide could play a major role in the symptoms of poor sleep of these patients. (+info)
Possible association of fibromyalgia with a polymorphism in the serotonin transporter gene regulatory region.
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OBJECTIVE: To analyze the genotypes of the promoter region of the serotonin transporter gene (5-HTT) in patients with fibromyalgia (FM). METHODS: Genomic DNA from 62 patients meeting the American College of Rheumatology 1990 criteria for FM and 110 healthy controls was analyzed by polymerase chain reaction. Additionally, the psychopathologic state of 52 of the FM patients was evaluated using the Beck Depression Inventory (BDI) and the Symptom Checklist-90-Revised (SCL-90-R). RESULTS: The 5-HTTLPR genotypes in FM patients versus controls were distributed as follows: L/L 27% versus 34%, L/S 42% versus 50%, and S/S 31% versus 16%. FM patients with the S/S genotype had higher mean scores on the BDI and the SCL-90-R compared with those in the L/L and L/S groups. CONCLUSION: A higher frequency of the S/S genotype of 5-HTT was found in FM patients compared with healthy controls. The S/S subgroup exhibited higher mean levels of depression and psychological distress. These results support the notion of altered serotonin metabolism in at least a subgroup of patients with FM. (+info)
A case report of an unusual case of nodular fasciitis in the orbit presenting with unilateral proptosis is described, and the radiological features are outlined. The histological features are discussed and the benign nature of the lesion stressed. Nodular fasciitis arising in the orbit and presenting as unilateral proptosis has not previously been reported in the literature. (+info)
Chronic Fatigue Syndrome and Primary Fibromyalgia Syndrome as recognized by GPs.
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BACKGROUND: Prevalence studies on Chronic Fatigue Syndrome (CFS) are rare. Because of the similarity in symptoms, the prevalence of Primary Fibromyalgia Syndrome (PFS) was investigated at the same time. OBJECTIVES: To determine the prevalence of CFS and PFS as recognized by GPs in The Netherlands and to inform them of the existence of CFS. METHODS: A postal questionnaire was sent to all GPs. RESULTS: The questionnaire was returned by 60% of the GPs. Seventy-three per cent reported one or more CFS patients and 83% one or more PFS patients in their practice. CONCLUSION: The estimated prevalence of CFS as recognized by GPs of 112 (PFS 157) patients per 100,000 is a minimum estimate. (+info)