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Results for “Surrogate variables analysis”

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At least 253 records · Page 14Linked to original sources

PubMed2006

Redefining cancer-related asthenia-fatigue syndrome.

BACKGROUND: Asthenia fatigue syndrome (AFS) is a common symptom perceived by patients with cancer and consists of reported pathologic fatigue, poor endurance, and impaired motor and cognitive function. OBJECTIVE: The purpose of this study was to examine the relationship between a traditional measure of AFS, visual analogue scale (VAS) fatigue ratings, and a set of more objective functional and physiologic measures (Dietz oncology classification, C-reactive protein, serum albumin, hemoglobin, body mass index [BMI]), Motor Functional Independence Measure (FIM) Score, Cognitive FIM Score. We hypothesized a relationship could suggest the utility of alternative means of assessing and addressing AFS. METHODS: We retrospectively examined the records of 131 patients admitted to our facility for inpatient rehabilitation because of disability-causing cancer or its treatment. RESULTS: Of our sample, 94.7% (124 cases) indicated at least mild fatigue and 97.7% (128 cases) showed abnormal serum albumin, C-reactive protein, hemoglobin, or BMI. We used multiple regression analysis to examine the relationship between VAS fatigue ratings and the aforementioned set of functional and physiologic variables. The regression explained a significant proportion of the variability in VAS fatigue ratings (F = 2.25, df = 7,123, p = 0.03, R = 0.34, R(2) = 0.11). However, only Motor FIM Score accounted for a significant independent contribution to the variability in VAS fatigue ratings. CONCLUSION: The data indicate physiologic and functional variables may provide an alternative, objective, and reliable operational definition of AFS. Specifically, using Motor FIM Score, as a surrogate for VAS fatigue ratings may be used to measure the efficacy of AFS treatment.

Activities of Daily Living↗

PubMed2006

Impact of antibiotic guideline compliance on duration of mechanical ventilation in critically ill patients with community-acquired pneumonia.

OBJECTIVE: Multiple guidelines exist to aid clinicians in choosing antibiotics to treat patients with severe community-acquired pneumonia (SCAP). Our goal was to assess the impact of following these guidelines, such as those from the Infectious Disease Society of America (IDSA), on the duration of mechanical ventilation (MV). DESIGN: Analysis of a prospective registry. SETTING: Multiple ICUs in Spain. PATIENTS: ICU patients with SCAP requiring > or = 24 h of endotracheal intubation and surviving their ICU course. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Demographics, comorbid diseases, severity of illness, and process of care variables were recorded. The duration of MV in patients receiving an antibiotic regimen consistent with IDSA guidelines was compared to patients with prescriptions not in accordance with IDSA recommendations. In the cohort (n = 199), Streptococcus pneumoniae was the most frequent pathogen, and unadjusted analysis showed that the duration of MV was longer in persons receiving IDSA-noncompliant regimens (11 days vs 10 days). In a multivariate hazard model, two variables were independently associated with greater durations of MV: development of acute renal failure (hazard ratio, 1.47; 95% confidence interval [CI], 1.02 to 2.12), and prescription of an IDSA-noncompliant regimen (hazard ratio, 1.40; 95% CI, 1.02 to 1.93). Adjusted analysis indicated that patients receiving treatment that was not compliant with IDSA guidelines received MV an added 3 days. CONCLUSION: Failure to follow antibiotic recommendations for the treatment of SCAP may increase the need for continuing MV. Conversely, guideline compliance could represent a surrogate marker that captures other aspects of clinical care, rather than be the direct factor leading to better outcomes. Nonetheless, given the costs associated with MV, enhanced guideline compliance may represent a means for improving outcomes and enhancing resource utilization.

Aged↗

PubMed2006

Cutoff values of surrogate measures of insulin resistance for metabolic syndrome in Korean non-diabetic adults.

We investigated the cutoff values of surrogate of insulin resistance for diagnosing metabolic syndrome in Korean adults. The data from 976 non-diabetic individuals (484 men and 492 women) aged 30-79 yr were analyzed. We determined the odds ratios for the prevalence of metabolic syndrome according to the quartiles of fasting insulin, homeostasis model for insulin resistance (HOMA-IR), and quantitative insulin sensitivity check index (QUICKI) as independent variables, while adjusting for age, sex, and body mass index. The cutoff values of fasting insulin, HOMA-IR, and QUICKI were estimated by the areas under the receiver-operating characteristic (ROC) curves. The cutoff points for defining insulin resistance are a fasting insulin level of 12.94 microU/mL, HOMA-IR=3.04 as the 75th percentile value, and QUICKI=0.32 as the 25th percentile value. Compared with the lowest quartile, the adjusted odds ratios for the prevalence of metabolic syndrome in the highest quartiles of fasting insulin, HOMA-IR, and QUICKI were 1.95 (1.26-3.01), 2.27 (1.45-3.56), and 2.27 (1.45-3.56), respectively. The respective cutoff values for fasting serum insulin, HOMA-IR, and QUIC-KI by ROC analysis were 10.57 microU/mL (sensitivity 58.5%, specificity 66.8%), 2.34 (sensitivity 62.8%, specificity 65.7%), and 0.33 (sensitivity 61.2%, specificity 66.8%). Fasting insulin, HOMA-IR, and QUICKI can be used as surrogate measures of insulin resistance in Korean non-diabetic adults.

Adult↗

PubMed1980

Statistical studies of mortality and air pollution. Multiple regression analyses by cause of death.

Multiple regression analyses are presented relating community air quality, socioeconomic variables, and mortality rates for all cancers, respiratory system cancer, respiratory disease, and external causes, for U.S. cities for 1969-1971. Socioeconomic variables included an index of cigarette smoking (by state), which was usually highly significant. Most air pollution variables were not significant, however, with the exception of the trace metal manganese, which was associated with cancers and respiratory disease. Because of the low ambient concentrations in this study, it is likely that manganese is serving as a surrogate for some other effect, such as occupational influences for example.

Air Pollution↗

PubMed2003

Predicting length of stay out of hospital following lung resection using preoperative health status measures.

Studies evaluating predictors of operative outcome for lung resection have focused on physiological measures of cardiorespiratory impairment, but these have proved inadequate. This study evaluated the predictive abilities of six preoperative variables: the global quality of life (QL), social function (SF), and emotional function (EF) scales of the European Organization for the Research and Treatment of Cancer's (EORTC) QLQ-C30 questionnaire, 6-min walk distance (6MWD), forced expiratory volume (FEV1), and diffusion capacity (DLCO). Operative outcome was represented by the surrogate measure length of stay, out of hospital within the first 30 days (LOSOH). A single-centre prospective cohort study evaluating 70 subjects was conducted using multiple regression. LOSOH was bimodally distributed, therefore analysis was undertaken for the entire sample and for two separate groups (A and B). Group B (n = 4) experienced severe complications (LOSOH = 0-5 days) and was too small for statistical analysis. Group A (n = 66) suffered fewer and less severe complications (LOSOH = 14-26 days). For the entire sample, age was the sole predictor of LOSOH (R2 = 0.123, p = 0.003). In Group A, the strongest predictors of LOSOH were global QL score and 6MWD (R2 = 0.224, p < 0.001). LOSOH was inversely correlated with complications. While it remains difficult to predict severe complications in this population, within Group A, health status measures demonstrated a limited ability to predict LOSOH.

Aged↗

PubMed2003

ZAP-70 expression as a surrogate for immunoglobulin-variable-region mutations in chronic lymphocytic leukemia.

BACKGROUND: The mutational status of immunoglobulin heavy-chain variable-region (IgVH) genes in the leukemic cells of chronic lymphocytic leukemia (CLL) is an important prognostic factor in the disease. We investigated whether the expression of ZAP-70 by CLL cells correlated with the IgVH mutational status, disease progression, and survival. METHODS: The expression of ZAP-70 was analyzed in T-cell and B-cell lines and in peripheral-blood samples from 56 patients with CLL with the use of flow cytometry, Western blotting, and immunohistochemistry. The results were correlated with the IgVH mutational status and clinical outcome. RESULTS: ZAP-70 was detected by flow-cytometric analysis in cells of T-cell lineage and in leukemic cells from 32 of 56 patients with CLL. In all patients in whom at least 20 percent of the leukemic cells were positive for ZAP-70, IgVH was unmutated, whereas IgVH mutations were found in 21 of 24 patients in whom less than 20 percent of the leukemic cells were positive for ZAP-70 (P<0.001). Concordant results were obtained when ZAP-70 expression was assessed by immunohistochemistry or Western blotting. The level of ZAP-70 expression did not change over time (median, 37 months) in sequential samples from 30 patients with CLL. Patients with Binet stage A CLL who had at least 20 percent ZAP-70-positive leukemic cells had more rapid progression and poorer survival than those with less than 20 percent ZAP-70-positive cells. CONCLUSIONS: Among patients with CLL, expression of ZAP-70, as detected by flow-cytometric analysis, correlated with IgVH mutational status, disease progression, and survival.

ADP-ribosyl Cyclase↗

PubMed2000

FEV(6) is an acceptable surrogate for FVC in the spirometric diagnosis of airway obstruction and restriction.

We analyzed the FEV(1)/FEV(6) and FEV(1)/FVC results of 502 consecutive patients in the spirometric diagnosis of airway obstruction. We also examined the agreement between FEV(6) and FVC in the spirometric diagnosis of restriction. Technically acceptable test results were obtained from 337 subjects (67%). The sensitivity of FEV(1)/FEV(6) for diagnosing airway obstruction as defined by FEV(1)/ FVC was 95.0%; the specificity was 97.4%. When interpretations differed, the measured values were all close to the lower limits of the reference ranges. When analysis included +/- 100-ml variability in FEV(1) and FEV(6), the sensitivity increased to 99.5% and the specificity to 100%. The reproducibility of FEV(6) was superior to that of FVC. These results suggest that FEV(6) is an accurate, reliable alternative to FVC for diagnosing airway obstruction and that FEV(6) is reasonably comparable to FVC for the spirometric diagnosis of restriction. FEV(6) is more reproducible and less physically demanding for patients.

Adult↗

PubMed2006

B cell chronic lymphocytic leukaemia/small lymphocytic lymphoma: role of ZAP70 determination on bone marrow biopsy specimens.

BACKGROUND: The course of chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL) partly depends on the mutational status of the variable region of immunoglobulin heavy chain genes (IgV(H)), which defines two subgroups of tumours: mutated and unmutated. The expression of zeta-associated protein 70 (ZAP70) is significantly associated with the more aggressive unmutated forms. AIMS: To assess the feasibility of the ZAP70 immunohistochemical test on bone-marrow biopsy (BMB) specimens and to compare the results with those of western blotting (WB) and IgV(H) mutational status assessed on neoplastic cells from peripheral blood. METHODS: 26 patients with CLL/SLL detected on BMB and with known IgV(H) mutational status were selected. ZAP70 was determined by immunohistochemistry (IHC) comparing three antibodies from different sources (Upstate, Cell Signaling, Santa Cruz, California, USA) and two different methods (APAAP and EnVision(+)). In 23 cases, ZAP70 WB results were also available. RESULTS: ZAP70 determination on BMB specimens turned out to be easily feasible with routine procedures with reagents from Upstate and Cell Signaling. The results were concordant with those obtained with WB and mutational status analysis in >80% of the cases with both reagents. Three of four discordant cases were mutated/ZAP70 positive, with two staining weakly for ZAP70 on both WB and IHC. CONCLUSIONS: The study confirms the role of ZAP70 as a possible surrogate of mutational status and emphasises its application in routine diagnostics; it discloses a small subset of discordant cases (mutated/ZAP70 weakly positive) that clinically cluster with the more favourable forms.

Aged↗

PubMed2002

Non-linear dynamics of operant behavior: a new approach via the extended return map.

Previous efforts to apply non-linear dynamic tools to the analysis of operant behavior revealed some promise for this kind of approach, but also some doubts, since the complexity of animal behavior seemed to be beyond the analyzing ability of the available tools. We here outline a series of studies based on a novel approach. We modified the so-called 'return map' and developed a new method, the 'extended return map' (ERM) to extract information from the highly irregular time series data, the inter-response time (IRT) generated by Skinner-box experiments. We applied the ERM to operant lever pressing data from rats using the four fundamental reinforcement schedules: fixed interval (FI), fixed ratio (FR), variable interval (VI) and variable ratio (VR). Our results revealed interesting patterns in all experiment groups. In particular, the FI and VI groups exhibited well-organized clusters of data points. We calculated the fractal dimension out of these patterns and compared experimental data with surrogate data sets, that were generated by randomly shuffling the sequential order of original IRTs. This comparison supported the finding that patterns in ERM reflect the dynamics of the operant behaviors under study. We then built two models to simulate the functional mechanisms of the FI schedule. Both models can produce similar distributions of IRTs and the stereotypical 'scalloped' curve characteristic of FI responding. However, they differ in one important feature in their formulation: while one model uses a continuous function to describe the probability of occurrence of an operant behavior, the other one employs an abrupt switch of behavioral state. Comparison of ERMs showed that only the latter was able to produce patterns similar to the experimental results, indicative of the operation of an abrupt switch from one behavioral state to another over the course of the inter-reinforcement period. This example demonstrated the ERM to be a useful tool for the analysis of IRT accompanying intermittent reinforcement schedules and for the study of the non-linear dynamics of operant behavior.

Animals↗

PubMed2006

Understanding economic outcomes in critical care.

PURPOSE OF REVIEW: The high costs of critical illness make economic outcomes important adjuncts to clinical outcomes in intensive care unit research. Costs are markedly different than other clinical outcomes, both in their measurement and their interpretation. RECENT FINDINGS: Although not necessarily patient-centered, economic outcomes are important to society. Costs are also useful summary measures of less-meaningful surrogates such as organ failures and lengths of stay. Limitations of economic outcomes, however, are numerous. Accurate measurement of costs in the ICU requires a thorough consideration of both direct and indirect costs, an understanding of the fixed and variable components of critical care expenditures, and knowledge that reducing resource use saves only the marginal, versus average, cost of ICU resources. Costs must also be interpreted alongside measures of effectiveness using proper modeling techniques. Interpretation can vary based on choice of effectiveness measure, perspective of the analysis, and societal and cultural norms. SUMMARY: When correctly measured and interpreted alongside measures of effectiveness, costs are a useful and important outcome in critical care research.

Cost-Benefit Analysis↗

PubMed1999

Effect of human immunodeficiency virus infection on serum beta2-microglobulin levels in pregnant women.

OBJECTIVE: To assess serum beta2-microglobulin levels in human immunodeficiency virus (HIV)-infected and uninfected pregnant women, variations of serum beta2-microglobulin levels during pregnancy and postpartum, factors that might influence beta2-microglobulin levels in pregnant women, and the association between beta2-microglobulin and perinatal HIV-1 transmission. METHODS: We assayed 374 stored (-70C) serum samples from pregnant women enrolled in the Newark perinatal HIV-1-transmission study and 18 nonpregnant women for beta2-microglobulin using a microparticulate enzyme immunoassay. The Student t test, Wilcoxon rank test, binomial test, and Spearman correlation coefficient were used for statistical analysis, with P < .05 considered statistically significant. A linear regression model was used to assess the effect of independent variables on serum beta2-microglobulin levels. RESULTS: There were no significant differences (P = .16) in serum beta2-microglobulin levels between pregnant and nonpregnant HIV-negative women (1.07+/-0.35 versus 0.99+/-0.18 mg/L). Beta2-Microglobulin levels did not vary throughout pregnancy and postpartum, irrespective of HIV serostatus. Substance abuse did not alter beta2-microglobulin levels. Human immunodeficiency virus infection caused significant increases of this surrogate marker, but it could not discriminate among disease stages. Beta2-Microglobulin levels at delivery were lower among women who delivered HIV-infected infants. CONCLUSION: Human immunodeficiency virus infection was associated with increased serum beta2-microglobulin levels in pregnant women and was the most significant correlate of increases of that marker. Pregnancy and substance use during pregnancy did not influence levels of serum beta2-microglobulin significantly.

Adult↗

PubMed1995

A microtiter plate assay for measurement of serum alanine aminotransferase in blood donors.

BACKGROUND: Alanine aminotransferase (ALT) testing in blood donors is required in many countries as a surrogate test for viral hepatitis. Current automated ALT assays do not fulfill some operational requirements of blood banks. STUDY DESIGN AND METHODS: The standard ALT measurement method of the International Federation of Clinical Chemistry was adapted to the 96-well microtiter plate to obtain optimal conditions. The method was compared with a reference biochemical method using an analyzer on 251 serum samples. RESULTS: The analytical variability was minimal (2.3% for an ALT level of 59 IU/L and 3.6% for an ALT level of 33 IU/L) after a total analysis time of 8 minutes and a time of 7 minutes before the first reading. With these measures, a linear standard curve was obtained in the range of 10 to 130 IU per L.A computerized validation procedure allowed rejection of samples with high ALT levels. Comparison with the analyzer gave a correlation coefficient, r = 0.935. The method proved to be efficient and time-saving in routine use over an 8-month period. CONCLUSION: The microtiter plate ALT assay is helpful in allowing the simultaneous distribution of ALT and immunoenzymatic assays. It provides accurate results and a minimal risk of false-negative results.

Alanine Transaminase↗

PubMed2000

Additive isotonic regression models in epidemiology.

Stone's method for assessing disease risk around a point source through isotonic regression is routinely used in spatial epidemiology. It is useful in situations where the relationship of risk with exposure (distance being commonly used as a surrogate variable) is assumed monotonic but otherwise of unknown form. This paper extends this method to non-spatial epidemiology, where typically two or more risk factors are present. The methodology described is based on the additive isotonic model approach of Bacchetti; versions appropriate to count (Poisson) data and case-control (binomial) data are described. In both cases, adjustment for covariates is incorporated, and a Monte Carlo method of hypothesis testing and interval estimation is presented. The methodology is illustrated through a case-control example concerning the analysis of the possible effect of preconceptional external ionizing radiation doses on the sex ratio at birth among children of fathers working at the Sellafield nuclear installation, Cumbria, U.K.

Case-Control Studies↗

PubMed1992

Statistical model to determine the relationship of response and survival in patients with advanced ovarian cancer treated with chemotherapy.

BACKGROUND: A statistically appropriate analysis of the association between survival and response measures in patients with ovarian cancer could help to define the role of response rate in planning, monitoring, and interpreting the results of clinical trials. PURPOSE: This study was designed to investigate the relationship between antitumor response determined by clinical or pathological means and survival in patients with advanced ovarian cancer with no previous treatment. We focused on avoiding the limitations of the usual approach of comparing durations of survival for patients responding to therapy with those for nonresponders. METHODS: A new meta-analytic statistical model we developed was used to analyze data from 26 randomized clinical trials published between 1975 and 1989. Our model incorporates intra-study and inter-study sources of variability in the estimates of response and survival. The study also addresses the methodological problems of evaluating response as a surrogate end point and the relevance of this association to clinical decision making and the design of clinical trials. RESULTS: For 13 studies in which response was pathologically assessed, an improvement in surgically documented complete response rate was associated with an increase in median survival. A similar but apparently smaller effect was found for the association between objective clinical response and median survival in the 25 studies reporting these data. CONCLUSIONS: These results suggest that therapeutic measures must produce large improvements in clinical response rates to achieve meaningful effects on median survival. Improvement in surgically documented complete response rate appears to be more strongly associated with increased median survival and, hence, might be used for interim monitoring in clinical trials, but the role of second-look procedures in clinical management is controversial.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1992

An assessment of the usefulness of demographic data provided by surrogate respondents in a case-control study of Parkinson's disease.

This study, based upon data from 40 non-demented Parkinson's disease cases and 101 community controls, and similar data provided by either the spouse (n = 110) or an adult child (n = 31) of each index subject, attempted to assess the usefulness of various demographic data provided by the surrogate respondents for the index subjects. The data were collected by personal interview using a structured questionnaire specifically developed for this study. Ninety-one percent of the index subjects and their surrogates provided information on the annual family income and 98% provided other demographic information. The analysis was done by three groups: the case-surrogates, the control-surrogates and the combined index subject-surrogates, and within each group by the two types of surrogates for the index subjects: the spouse vs adult child. The overall percent agreement between the index subjects and their surrogates varied from moderate for annual family income (54.1%), to good for educational level (61.6%) and to excellent for ethnic origin (82.6%), for age +/- 1 year (97.9%) and for marital status (100.0%). No significant differences in agreement were found for any of these demographic variables either between the case-surrogate group and the control-surrogate group, or between the spouse surrogates and the child surrogates. These findings suggest that spouses and adult children can provide valid information and are equally reliable informants concerning the demographic characteristics of index subjects in a case-control study of Parkinson's disease and, possibly, of other diseases.

Age Factors↗

PubMed2005

Bayesian hierarchical modelling to enhance the epidemiological value of abattoir surveys for bovine fasciolosis.

Four classes of Bayesian hierarchical models were evaluated using an historical dataset from an abattoir survey for fasciolosis conducted in Victoria, Australia. The purpose of this analysis was to identify areas of high prevalence and to explain these in terms of environmental covariates. The simplest of the Bayesian models, with a single random effect, validated the use of smoothed maps for cartographic display when the sample sizes vary. The model was then extended to partition the random effect into spatially structured and unstructured components, thus allowing for spatial autocorrelation. Rainfall, irrigation, temperature-adjusted rainfall and a remotely sensed surrogate for rainfall, the normalised difference vegetation index (NDVI), were then introduced into the models as explanatory variables. The variable that best explained the observed distribution was irrigation. Associations between prevalence and both rainfall and NDVI that were significant in fixed effects models were shown to be due to spatial confounding. Nevertheless, provided they are used cautiously, confounded variables may be valid predictors for the prevalence of disease.

Abattoirs↗

PubMedDate not supplied

US Army Chemical Corps Vietnam veterans health study: preliminary results.

The long-term health consequences of exposure to phenoxyherbicides used in Vietnam has been a great concern to the veterans. In addition to the Air Force Ranch Hand personnel, Army Chemical Corps personnel who served in Vietnam are thought to have had some of the highest herbicide exposures. The Department of Veterans Affairs commenced a study of veterans who served in Vietnam as members of the Army Chemical Corps and a comparison cohort of Army Chemical Corps personnel who served elsewhere. A total of 2872 Vietnam veterans and 2737 non-Vietnam veterans who served in the Army Chemical Corps were identified for inclusion in a telephone health interview survey with a random 20% sample of veterans receiving serum dioxin and other congeners assessments. In a feasibility study which included 284 Vietnam veterans and 281 non-Vietnam veterans, 100 serum assessments were conducted of which 95 were included in the analysis. Vietnam veterans with a history of spraying herbicides were found to have a statistically significant elevation in their current serum 2,3,7,8-TCDD concentrations compared to non-Vietnam veterans without a spray history (P = 0.05). Other 2,3,7,8-substituted dioxins levels were comparable to the levels found in the non-Vietnam veterans. This feasibility study demonstrated that serum dioxin concentrations from a sample of the study participants can be used to identify exposure variables in the health survey that can serve as a surrogate measure of phenoxyherbicide exposure.

Adult↗

PubMed2000

Recurrent patterns of atrial depolarization during atrial fibrillation assessed by recurrence plot quantification.

The aim of this study was to determine the presence of organization of atrial activation processes during atrial fibrillation (AF) by assessing whether the activation sequences are wholly random or are governed by deterministic mechanisms. We performed both linear and nonlinear analyses based on the cross correlation function (CCF) and recurrence plot quantification (RPQ), respectively. Recurrence plots were quantified by three variables: percent recurrence (PR), percent determinism (PD), and entropy of recurrences (ER). We recorded bipolar intra-atrial electrograms in two atrial sites during chronic AF in 19 informed subjects, following two protocols. In one, both recording sites were in the right atrium; in the other protocol, one site was in the right atrium, the other one in the left atrium. We extracted 19 episodes of type I AF (Wells' classification). RPQ detected transient recurrent patterns in all the episodes, while CCF was significant only in ten episodes. Surrogate data analysis, based on a cross-phase randomization procedure, decreased PR, PD, and ER values. The detection of spatiotemporal recurrent patterns together with the surrogate data results indicate that during AF a certain degree of local organization exists, likely caused by deterministic mechanisms of activation.

Adult↗