Regression Analysis in Health Services Research: The Use of Dummy Variables

Polissar, Lincoln; Diehr, Paula

doi:10.1097/00005650-198209000-00008

Cited by 86 publications

(38 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To assess the dependence of v p and K trans on histologic variables, a multiple regression analysis was performed. The F test from analysis of variance tables of two nested regression models was used to compare a model with one predictor variable (eg, K trans vs macrophages) with a model with an additional predictor variable (eg, K trans vs macrophages and necrotic core) (26). The null hypothesis of the F test in this example is that, when controlling for macrophage content, an additional histologic variable (eg, loose matrix) does not independently add to the prediction of K trans .…”

Section: Discussionmentioning

confidence: 99%

Inflammation in Carotid Atherosclerotic Plaque: A Dynamic Contrast-enhanced MR Imaging Study

et al. 2006

View full text Add to dashboard Cite

Purpose-To prospectively evaluate if there is an association between plaque enhancement at magnetic resonance (MR) imaging and proinflammatory cardiovascular risk factors and plaque content.Materials and Methods-This study was performed with informed consent, HIPAA compliance, and institutional review board approval. Contrast agent dynamics within carotid plaques were measured in 30 patients (29 men, one woman; mean age, 67.7 years ± 10.7 [standard deviation]) who were scheduled to undergo carotid endarterectomy. Measurements were based on kinetic modeling of images obtained at 15-second intervals during which a gadolinium-based contrast agent was injected. The time-varying signal intensities within the plaques were used to estimate the fractional plasma volume (v p ) and transfer constant (K trans ) of contrast material into the extracellular space. Pearson correlation coefficients were computed between blinded MR measurements and histologic measurements of plaque composition, including macrophages, neovasculature, necrotic core, calcification, loose matrix, and dense fibrous tissue. Correlation coefficients or mean differences were computed regarding clinical markers of cardiovascular risk.Results-Analyzable MR images and histologic results were obtained in 27 patients. Measurements of K trans correlated with macrophage (r = 0.75, P < .001), neovasculature (r = 0.71, P <.001), and loose matrix (r = 0.50, P = .01) content. Measurements of v p correlated with macrophage (r = 0.54, P = .004), neovasculature (r = 0.68, P <.001), and loose matrix (r = 0.42, P = .03) content. For clinical parameters, significant associations were correlated with K trans only, with decreased high-density lipoprotein levels (r = −0.66, P <.001) and elevated K trans measurements in smokers compared with nonsmokers (mean, 0.134 min −1 vs 0.074 min −1 , respectively; P = .01). Conclusion-The correlations between K trans and histologic markers of inflammation suggest thatK trans is a quantitative and non-invasive marker of plaque inflammation, which is further supported by the correlation of K trans with proinflammatory cardiovascular risk factors, decreased high-density lipoprotein levels, and smoking.Address correspondence to W.S.K. (e-mail: bkerwin@u.washington.edu).. Author contributions: Guarantor of integrity of entire study, W.S.K.; study concepts/study design or data acquisition or data analysis/ interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, W. Contrast material enhancement in carotid atherosclerotic plaques has been observed in several recent investigations with magnetic resonance (MR) imaging after the injection of clinically available gadolinium-based contrast agents (1-5). Strong contrast enhancement suggests the presence of a vascular supply to the plaque and increased endothelial permeability that facilitates the entry of the contrast agent from the blood plasma. Because neov...

show abstract

Section: Discussionmentioning

confidence: 99%

Inflammation in Carotid Atherosclerotic Plaque: A Dynamic Contrast-enhanced MR Imaging Study

et al. 2006

View full text Add to dashboard Cite

show abstract

“…The different definitions of complex karyotype coded in a variable with k-categories were transformed into k-1 dummy variables and added to the model. 15 All P values were 2-sided, and values less than .05 were considered statistically significant. Statistical analysis was performed using SPSS for Windows Version 15.0.1.…”

Section: Methodsmentioning

confidence: 99%

Complex karyotype newly defined: the strongest prognostic factor in advanced childhood myelodysplastic syndrome

Göhring

Michalova

Beverloo

et al. 2010

Blood

View full text Add to dashboard Cite

To identify cytogenetic risk factors predicting outcome in children with advanced myelodysplastic syndrome, overall survival of 192 children prospectively enrolled in European Working Group of Myelodysplastic Syndrome in Childhood studies was evaluated with regard to karyotypic complexity. Structurally complex constitutes a new definition of complex karyotype characterized by more than or equal to 3 chromosomal aberrations, including at least one structural aberration. Five-year overall survival in patients with more than or equal to 3 clonal aberrations, which were not structurally complex, did not differ from that observed in patients with normal karyotype. Cox regression analysis revealed the presence of a monosomal and structurally complex karyotype to be strongly associated with poor prognosis (hazard ratio ‫؍‬ 4.6, P < .01). Notably, a structurally complex karyotype without a monosomy was associated with a very short 2-year overall survival probability of only 14% (hazard ratio ‫؍‬ 14.5; P < .01). The presence of a structurally complex karyotype was the strongest independent prognostic marker predicting poor outcome in children with advanced myelodysplastic syndrome. (Blood. 2010; 116(19):3766-3769) IntroductionKaryotypic complexity has been reported to be associated with a poor prognosis in myeloid neoplasia. [1][2][3] However, the definition of a complex karyotype remains a matter of debate. Most studies defined a complex karyotype as more than or equal to 3 independent abnormalities. 2,[4][5][6] In the Medical Research Council Acute Myeloid Leukemia 10 (MRC AML10) trial, more than or equal to 5 independent abnormalities were required 3 because acute myeloid leukemia (AML) patients with more than or equal to 5 abnormalities had a significantly worse 5-year overall survival (OS) than those with 3 or 4 abnormalities. 1 Increased numbers of chromosomal abnormalities were also found to adversely influence median survival in adult myelodysplastic syndrome (MDS) patients. 7 Breems et al recently investigated the prognostic value of different cytogenetic components of a complex karyotype in adult AML and identified a monosomal karyotype (ie, either one single autosomal monosomy in the presence of at least one structural aberration or at least 2 distinct autosomal monosomies) as a highly unfavorable risk category. 8 To better stratify children with advanced MDS, we evaluated the outcome in 192 children prospectively diagnosed and treated within the studies of the European Working Group of MDS in Childhood (EWOG-MDS) related to karyotypic complexity. This study is registered at www.clinicaltrials.gov as #NCT00047268 and #NCT00662090. MethodsAll patients younger than 18 years with adequate cytogenetic studies and advanced MDS (ie, refractory anemia with excess blasts or refractory anemia with excess blasts in transformation), 9,10 enrolled in studies EWOG-MDS 98 (www.clinicaltrials.gov; #NCT00047268) or EWOG-MDS 2006 (#NCT00662090) between July 1, 1998 and June 30, 2008 were included in this analysis. In both stud...

show abstract

“…Two levels of prior comparisons were used. The first level tested for the presence of a linear (monotonically increasing or decreasing) trend within the four treatment phases of the study (two IL-2 and two offdrug) (45,46). In the second level, paired comparisons for differences among treatments were conducted, each averaging across the 5 d of observations within a treatment phase.…”

Section: Methodsmentioning

confidence: 99%

Evidence for cytokine-inducible nitric oxide synthesis from L-arginine in patients receiving interleukin-2 therapy.

Hibbs¹,

Westenfelder²,

Taintor³

et al. 1992

J. Clin. Invest.

481

160

View full text Add to dashboard Cite

An interferon-'y, tumor necrosis factor, and interleukin-1-inducible, high-output pathway synthesizing nitric oxide (NO) from L-arginine was recently identified in rodents. High-dose interleukin-2 (IL-2) therapy is known to induce the same cytokines in patients with advanced cancer. Therefore, we examined renal cell carcinoma (RCC; n = 5) and malignant melanoma (MM; n = 7) patients for evidence of cytokine-inducible NO synthesis. Activity of this pathway was evaluated by measuring serum and urine nitrate (the stable degradation product of NO) during IL-2 therapy. IL-2 administration caused a striking increase in NO generation as reflected by serum nitrate levels (10-and 8-fold increase IP < 0.001, P < 0.0031 for RCC and MM patients, respectively) and 24-h urinary nitrate excretion (6.5-and 9-fold increase [both P < 0.0011 for RCC and MM patients, respectively). IL-2-induced renal dysfunction made only a minor contribution to increased serum nitrate levels. Metabolic tracer studies using L-[guanidino-5N2Jarginine demonstrated that the increased nitrate production was derived from a terminal guanidino nitrogen atom of L-arginine. Our results showing increased endogenous nitrate synthesis in patients receiving IL-2 demonstrate for the first time that a cytokine-inducible, highoutput L-arginine/NO pathway exists in humans. (J. Clin. Invest. 1992. 89:867-877.) Key words: acute renal failure * malignant melanoma * nitrate * nitrite * renal cell carcinoma

show abstract

Regression Analysis in Health Services Research: The Use of Dummy Variables

Cited by 86 publications

References 6 publications

Inflammation in Carotid Atherosclerotic Plaque: A Dynamic Contrast-enhanced MR Imaging Study

Inflammation in Carotid Atherosclerotic Plaque: A Dynamic Contrast-enhanced MR Imaging Study

Complex karyotype newly defined: the strongest prognostic factor in advanced childhood myelodysplastic syndrome

Evidence for cytokine-inducible nitric oxide synthesis from L-arginine in patients receiving interleukin-2 therapy.

Contact Info

Product

Resources

About