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PubMed2005

Initially more rapid small intestinal glucose delivery increases plasma insulin, GIP, and GLP-1 but does not improve overall glycemia in healthy subjects.

The rate of gastric emptying of glucose-containing liquids is a major determinant of postprandial glycemia. The latter is also dependent on stimulation of insulin secretion by glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). Although overall emptying of glucose approximates 1-3 kcal/min, the "early phase" of gastric emptying is usually more rapid. We have evaluated the hypothesis that increased stimulation of incretin hormones and insulin by a more rapid initial rate of small intestinal glucose delivery would reduce the overall glycemic response to a standardized enteral glucose load. Twelve healthy subjects were studied on two separate days in which they received an intraduodenal (id) glucose infusion for 120 min. On one day, the infusion rate was variable, being more rapid (6 kcal/min) between t = 0 and 10 min and slower (0.55 kcal/min) between t = 10 and 120 min, whereas on the other day the rate was constant (1 kcal/min) from t = 0-120 min, i.e., on both days 120 kcal were given. Between t = 0 and 75 min, plasma insulin, GIP, and GLP-1 were higher with the variable infusion. Despite the increase in insulin and incretin hormones, blood glucose levels were also higher. Between t = 75 and 180 min, blood glucose and plasma insulin were lower with the variable infusion. There was no difference in the area under the curve 0-180 min for blood glucose. We conclude that stimulation of incretin hormone and insulin release by a more rapid initial rate of id glucose delivery does not lead to an overall reduction in glycemia in healthy subjects.

Adult↗
PubMed2005

The 1944-1945 Dutch famine and subsequent overall cancer incidence.

Caloric restriction seems to be the most potent dietary intervention to protect against a variety of cancers in animals. We investigated whether overall cancer risk is affected in humans after exposure to a brief famine, followed by a period of abundance. We used data of approximately 15,000 women who were exposed at various degrees to the 1944-1945 Dutch famine at ages between 2 and 33 years. Between 1983 and 1986, these women were asked about their individual experiences of famine exposure ("absent," "moderate," or "severe exposure"). During follow-up until January 2000, 1,602 new cancer cases were identified by the regional cancer registry. We assessed the relation between famine and total cancer risk by weighted Cox regression models, in which a 15% random sample was used to represent person-years lived in the entire cohort. In these models, we adjusted for potential confounders. Overall cancer risk was increased in women having been severely famine exposed compared with women having been unexposed (hazard ratio, 1.25; 95% confidence interval, 1.01-1.55). Exclusion of breast cancer cases from our analyses showed that this increase in risk was largely driven by the previously reported increase in breast cancer risk: women who were severely exposed to the famine were at a 1.12 (95% confidence interval, 0.87-1.43) times increased risk of non-breast cancer compared with the unexposed. In conclusion, we found no indications that this brief famine has affected overall cancer risk, exclusive of breast cancer. Counteracting increased caloric intake following the famine, however, may have obscured any relation.

Adolescent↗
PubMed2005

High mutagen sensitivity in peripheral blood lymphocytes predicts poor overall and disease-specific survival in patients with stage III non-small cell lung cancer treated with radiotherapy and chemotherapy.

PURPOSE: To investigate whether the bleomycin sensitivity assay, an in vitro peripheral blood lymphocyte assay, can predict outcome in patients with inoperable stage III non-small-cell lung cancer (NSCLC) treated with definitive radiotherapy and chemotherapy. EXPERIMENTAL DESIGN: We identified 102 patients with inoperable stage III NSCLC cell lung cancer treated with definitive radiotherapy and chemotherapy. The patients' pretreatment peripheral blood lymphocyte cultures were treated with the radiomimetic mutagen bleomycin. An index of bleomycin sensitivity was determined by counting the number of chromatid breaks in 50 metaphases. The correlation between bleomycin sensitivity (expressed as mean breaks per cell) and clinical outcome was analyzed. RESULTS: High bleomycin sensitivity (defined as a mean of >1.02 chromatid breaks/cell, representing the third quartile of bleomycin sensitivity) predicted poor disease-specific survival and overall survival. The 6-year disease-specific survival was 27% in patients with high bleomycin sensitivity compared with 46% in patients without such sensitivity (P = 0.0094). The association remained statistically significant when adjusted for smoking status, age, and radiation dose. The 6-year overall survival was 19% for patients with high bleomycin sensitivity and 29% for those without (P = 0.0193). There was a trend toward worse local regional control and worse disease-free survival among patients with high bleomycin sensitivity. There was no difference between the two groups in distant metastasis-free survival or radiation treatment-related complications. CONCLUSIONS: High bleomycin sensitivity correlated with poor overall survival and disease-specific survival in these patients with stage III NSCLC treated with radiotherapy and chemotherapy. Bleomycin sensitivity may function as a biomarker for poor clinical outcome for this group of patients.

Aged↗
PubMed2004

Humoral responses to peptides correlate with overall survival in advanced cancer patients vaccinated with peptides based on pre-existing, peptide-specific cellular responses.

PURPOSE: The aim of this study is to find a laboratory marker for overall survival in advanced cancer patients who were vaccinated with peptides based on pre-existing, peptide-specific CTL precursors in the circulation. EXPERIMENTAL DESIGN: A group of 113 patients with advanced cancer (28 colorectal, 22 prostate, 15 lung, 14 gastric, and 34 other cancers) was enrolled in a Phase I clinical study of peptide vaccination in which peptide-specific CTL precursors of prevaccination peripheral blood mononuclear cells were measured, followed by vaccination with these peptides (maximum of four). For cellular responses, pre and postvaccination (sixth) peripheral blood mononuclear cells were provided for measurement of both peptide-specific CTL precursors by IFN-gamma release assay and tumor reactivity by (51)Cr release assay. Delayed type hypersensitivity was also measured. For humoral response, pre and postvaccination (sixth) sera were provided for measurement of peptide-reactive IgG by an ELISA. RESULTS: The median survival time and 1-year survival rate of the total cases were 346 +/- 64.9 days and 44.6%, respectively, and those of patients vaccinated more than six times (n = 91) were 409 +/- 15 days and 54.4%, respectively. In these 91 patients, the overall survival of patients whose sera showed increased levels of peptide-reactive IgG (n = 60) was significantly more prolonged (P = 0.0003) than that of patients whose sera did not (n = 31), whereas none of cellular responses correlated with overall survival. CONCLUSIONS: Peptide-specific IgG in postvaccination sera could be a suitable laboratory maker for the prediction of prolonged survival in advanced cancer patients vaccinated with peptides based on pre-existing CTL precursors.

Adult↗
PubMed1990

Failure of substrate-induced gluconeogenesis to increase overall glucose appearance in normal humans. Demonstration of hepatic autoregulation without a change in plasma glucose concentration.

It has been proposed that increased supply of gluconeogenic precursors may be largely responsible for the increased gluconeogenesis which contributes to fasting hyperglycemia in non-insulin-dependent diabetes mellitus (NIDDM). Therefore, to test the hypothesis that an increase in gluconeogenic substrate supply per se could increase hepatic glucose output sufficiently to cause fasting hyperglycemia, we infused normal volunteers with sodium lactate at a rate approximately double the rate of appearance observed in NIDDM while clamping plasma insulin, glucagon, and growth hormone at basal levels. In control experiments, sodium bicarbonate was infused instead of sodium lactate at equimolar rates. In both experiments, [6-3H]-glucose was infused to measure glucose appearance and either [U-14C]lactate or [U-14C]alanine was infused to measure the rates of appearance and conversion of these substrates into plasma glucose. Plasma insulin, glucagon, growth hormone, C-peptide, and glycerol concentrations, and blood bicarbonate and pH in control and lactate infusion experiments were not significantly different. Infusion of lactate increased plasma lactate and alanine to 4.48 +/- 3 mM and 610 +/- 33 microM, respectively, from baseline values of 1.6 +/- 0.2 mM and 431 +/- 28 microM, both P less than 0.01; lactate and alanine rates of appearance increased to 38 +/- 1.0 and 8.0 +/- 0.3 mumol/kg per min (P less than 0.01 versus basal rates of 14.4 +/- 0.4 and 5.0 +/- 0.5 mumol/kg per min, respectively). With correction for Krebs cycle carbon exchange, lactate incorporation into plasma glucose increased nearly threefold to 10.4 mumol/kg per min and accounted for about 50% of overall glucose appearance. Alanine incorporation into plasma glucose increased more than twofold. Despite this marked increase in gluconeogenesis, neither overall hepatic glucose output nor plasma glucose increased and each was not significantly different from values observed in control experiments (10.8 +/- 0.5 vs. 10.8 +/- 0.5 mumol/kg per min and 5.4 +/- 0.4 vs. 5.3 +/- 0.3 mM, respectively). We, therefore, conclude that in normal humans there is an autoregulatory process independent of changes in plasma glucose and glucoregulatory hormone concentrations which prevents a substrate-induced increase in gluconeogenesis from increasing overall hepatic glucose output; since this process cannot be explained on the basis of inhibition of gluconeogenesis from other substrates, it probably involves diminution of glycogenolysis. A defect in this process could explain at least in part the increased hepatic glucose output found in NIDDM.

Alanine↗
PubMed1997

Prevalence of pain combinations and overall pain: a study of headache, stomach pain and back pain among school-children.

The prevalence of pain combinations among school children is addressed in view of earlier findings of high pain prevalence in this population. The study considers the prevalence of combinations of three common pains headache, stomach pain and back pain-in a random national sample of 2173 Icelandic 11-12 and 15-16 year-old school children. According to the results from this study there is a 78.2% prevalence of monthly pain. One or more instances of weekly pain is experienced by 40.4% of the children, and 15.6% experience two or three pains weekly. Relevance of gender is greater when dealing with combinations of monthly than weekly pain. Combinations of weekly pains are more gender related than single weekly pains. Girls have significantly more frequent overall pain than boys. The distribution of pain combinations varies by age but not overall pain. The study yields important information about the extent of the overall problem of pain among school children and indicates the need to further study the correlates of different pain combinations in this age group.

Abdominal Pain↗
PubMed2001

Is overall asthma control being achieved? A hypothesis-generating study.

The efficacy of asthma therapy is traditionally measured using single end-points. In contrast, the aim of therapy is to achieve overall control, defined by management guidelines as achieving a number of treatment goals. These goals reflect expert opinion, rather than being evidence based. The objective of this study was to determine whether guideline-defined asthma control is achievable. Eight studies of salmeterol/fluticasone propionate combination therapy were analysed using three asthma control measures of varying stringency, derived from the guideline goals. For each measure, only patients meeting all goals were classified as controlled. The analysis demonstrated that asthma control, as defined by management guidelines, can be achieved. For a given therapy, similar proportions of patients achieved control irrespective of disease severity, suggesting that outcome expectations should not be reduced for patients with more severe disease. Substantially more patients achieved the target values for individual goals than achieved overall control, indicating that reliance on individual end-points is likely to result in significant overestimation of true control. The findings of this hypothesis-generating study should be prospectively tested. Future research will include a randomized controlled study designed to assess the proportion of patients able to achieve overall control of asthma when treatment is titrated appropriately.

Albuterol↗
PubMed2004

Upper gastrointestinal and overall tolerability of alendronate once weekly in patients with osteoporosis: results of a randomized, double-blind, placebo-controlled study.

OBJECTIVE: To compare the upper gastrointestinal (GI) and overall tolerability profiles of alendronate 70 mg once weekly with placebo. RESEARCH DESIGN AND METHODS: This 12-week international, multi-center, randomized, double-blind, placebo-controlled trial included 449 postmenopausal women and men with osteoporosis at 44 sites in 19 countries in Europe, the Americas, Africa, and Asia-Pacific. Subjects were randomized to alendronate 70 mg once weekly or matching placebo in a 1:1 ratio. MAIN OUTCOME MEASURES: The safety and tolerability of weekly alendronate and placebo were captured as clinical and laboratory adverse events. The primary endpoint was upper GI tolerability based on the incidence of upper GI tract adverse events. Secondary endpoints included the percentage of subjects who discontinued therapy due to a drug-related upper GI adverse event. Change from baseline in bone turnover as measured by the urinary N-telopeptide-collagen crosslinks corrected for creatinine (NTx/Cr) was assessed at 12 weeks as an indicator of efficacy. RESULTS: The percentages of subjects reporting an upper GI tract adverse event in the alendronate 70 mg once weekly group (9.8%) and the placebo group (9.4%) were similar. The risk difference between the two treatment groups (alendronate minus placebo) was 0.4% [95% confidence interval (CI), -5.1%, 5.9%]. Percentages of subjects who discontinued due to a drug-related upper GI adverse event were also similar (alendronate 2.7%; placebo 2.2%; risk difference 0.4%, 95% CI, -2.4, 3.3). The overall tolerability profile of alendronate 70 mg once weekly, as measured by the percentage 8.0% (95% CI, 1.4%, 15.0%) increase in the of subjects reporting any adverse event, was similar to that of placebo (risk difference 2.1%, 95% CI -6.9, 11.0). There was a significant 43.3% (95% CI, -47.9%, -38.3%) decrease from baseline in urinary NTx/Cr in the alendronate group compared with an placebo group at Week 12. CONCLUSION: Alendronate 70 mg administered once weekly to women and men with osteoporosis has an upper GI and overall tolerability profile similar to that of placebo.

Administration, Oral↗
PubMed2005

The efficacy of tadalafil in improving sexual satisfaction and overall satisfaction in men with mild, moderate, and severe erectile dysfunction: a retrospective pooled analysis of data from randomized, placebo-controlled clinical trials.

BACKGROUND: Satisfaction with the sexual experience is considered important when evaluating the impact of treatments for erectile dysfunction (ED), yet satisfaction has been infrequently assessed in clinical trials. OBJECTIVE: To evaluate satisfaction with, and enjoyment of, the sexual experience in men with ED enrolled in 11 placebo-controlled clinical trials of tadalafil. STUDY DESIGN AND METHODS: Retrospective pooled analysis of data from 11 randomized, double blind, placebo-controlled clinical trials of tadalafil. Men with mild (N = 838), moderate (N = 558), or severe (N = 703) ED who were randomized to tadalafil 10 mg or 20 mg or placebo taken as needed for 12 weeks were included in this analysis. Efficacy measures included the International Index of Erectile Function (IIEF). Reported herein are the scores on the IIEF overall satisfaction domain and individual IIEF questions (IIEF-Q7, satisfaction with intercourse; and IIEF-Q8, enjoyment of intercourse). RESULTS: At least moderate satisfaction (IIEF overall satisfaction domain) was reported by 55% and 72% of patients with mild ED taking tadalafil 10 mg and 20 mg, respectively, compared with 33% taking placebo (p < 0.002); 60% and 65% vs. 19% of patients with moderate ED (p < 0.001); and 32% and 49% vs. 9% with severe ED (p < 0.001). Satisfactory intercourse during most attempts or almost always/always (IIEF-Q7) was reported by 59% and 79% of patients with mild ED taking tadalafil 10 mg and 20 mg vs. 32% taking placebo (p < 0.001); 52% and 65% vs. 18% with moderate ED (p < 0.001); and 28% and 49% vs. 5% with severe ED (p < 0.001). Highly or very highly enjoyable intercourse (IIEF-Q8) was reported by 45% and 63% of patients with mild ED taking tadalafil 10 mg and 20 mg vs. 21% taking placebo (p < 0.001); 43% and 56% vs. 16% with moderate ED (p < 0.001); and 19% and 44% vs. 5% with severe ED (p < 0.001). CONCLUSIONS: Compared with placebo, tadalafil 10 mg and 20 mg improved overall satisfaction with the sexual experience, intercourse satisfaction, and intercourse enjoyment in men with mild, moderate, and severe ED.

Adult↗
PubMed2006

Polychotomization of continuous variables in regression models based on the overall C index.

BACKGROUND: When developing multivariable regression models for diagnosis or prognosis, continuous independent variables can be categorized to make a prediction table instead of a prediction formula. Although many methods have been proposed to dichotomize prognostic variables, to date there has been no integrated method for polychotomization. The latter is necessary when dichotomization results in too much loss of information or when central values refer to normal states and more dispersed values refer to less preferable states, a situation that is not unusual in medical settings (e.g. body temperature, blood pressure). The goal of our study was to develop a theoretical and practical method for polychotomization. METHODS: We used the overall discrimination index C, introduced by Harrel, as a measure of the predictive ability of an independent regressor variable and derived a method for polychotomization mathematically. Since the naïve application of our method, like some existing methods, gives rise to positive bias, we developed a parametric method that minimizes this bias and assessed its performance by the use of Monte Carlo simulation. RESULTS: The overall C is closely related to the area under the ROC curve and the produced di(poly)chotomized variable's predictive performance is comparable to the original continuous variable. The simulation shows that the parametric method is essentially unbiased for both the estimates of performance and the cutoff points. Application of our method to the predictor variables of a previous study on rhabdomyolysis shows that it can be used to make probability profile tables that are applicable to the diagnosis or prognosis of individual patient status. CONCLUSION: We propose a polychotomization (including dichotomization) method for independent continuous variables in regression models based on the overall discrimination index C and clarified its meaning mathematically. To avoid positive bias in application, we have proposed and evaluated a parametric method. The proposed method for polychotomizing continuous regressor variables performed well and can be used to create probability profile tables.

Bias↗
PubMed1998

MOPP/ABV hybrid chemotherapy for advanced Hodgkin's disease significantly improves failure-free and overall survival: the 8-year results of the intergroup trial.

PURPOSE: To compare the efficacy of sequential mechlorethamine, vincristine, procarbazine, and prednisone (MOPP) followed by doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD) versus the MOPP/ABV hybrid regimen in advanced-stage Hodgkin's disease. PATIENTS AND METHODS: A total of 737 patients with previously untreated stages III2A, IIIB, IVA, or IVB Hodgkin's disease and patients in first relapse after radiotherapy were prospectively randomized to sequential MOPP-ABV or MOPP/ABV hybrid. Of 691 eligible patients, 344 received the sequential regimen and 347 received the hybrid. RESULTS: The overall response rate was 95%, with complete responses (CRs) in 79%: 83% on the MOPP/ABV hybrid and 75% on the sequential MOPP-ABVD arm (P = .02). With a median follow-up time of 7.3 years, the 8-year failure-free survival (FFS) rates were 64% for MOPP/ABV hybrid and 54% far sequential MOPP-ABVD (P = .01; 0.69 relative risk of failure, comparing MOPP/ABV hybrid v MOPP-ABVD). The 8-year overall survival rate was significantly better for the MOPP/ABV hybrid (79%) as compared with sequential MOPP-ABVD (71%) (P = .02; relative risk, 0.65). MOPP/ABV hybrid had significantly more life-threatening or fatal neutropenia and pulmonary toxicity than the sequential MOPP-ABVD arm, which was associated with significantly greater thrombocytopenia. Nine cases of acute myelogenous leukemia or myelodysplasia were reported on the sequential regimen as compared with only one on the hybrid (P = .01). CONCLUSION: MOPP/ABV hybrid chemotherapy was significantly more effective than sequential MOPP-ABVD. FFS and overall survival were significantly improved on the hybrid arm, which was also associated with a lower incidence of acute leukemia or myelodysplasia.

Adolescent↗
PubMed1998

Randomized comparison of four tools measuring overall quality of life in patients with advanced cancer.

PURPOSE: We report on a clinical trial developed to compare four different instruments that provide overall quality-of-life (QOL) scores, ranging from a simple, one-item instrument to more detailed instruments. Two issues addressed were (1) Will QOL tools suffer from missing data when used in a community-based cooperative group setting?, and (2) Are there additional data generated by a more detailed multiitem instrument over that provided by a single-item global QOL question? MATERIALS AND METHODS: A four-arm randomized trial was designed to compare four instruments that provide overall QOL scores in patients with advanced colorectal cancer. Patients and physicians completed the single-item Spitzer Uniscale (UNISCALE) at baseline and monthly. Patients were randomly assigned to complete, in addition, either the 22-item Functional Living Index-Cancer (FLIC), the five-item Spitzer QOL index (QLI), a picture-face scale (PICT), or nothing else. RESULTS: A total of 128 patients were randomized. Greater than 90% complete QOL data were obtained. There was strong correlation, concordance, and criterion-related validity among all four patient-completed tools. The UNISCALE had a greater decrease over time than did the FLIC (P=.005), which suggests a greater sensitivity; the UNISCALE was similar to the QLI and the PICT in this regard. Physicians provided lower UNISCALE scores than patients. Results supported the hypothesis that QOL is prognostic for survival. CONCLUSION: Patients can effectively complete QOL tools in a cooperative group setting with proper education of health care providers and patients. A simple single-item tool (UNISCALE) appears to be appropriate to obtain a measure of overall QOL.

Body Weight↗
PubMed1994

Local control versus dose or overall time: from coefficients to percentages.

When clinical results are analysed to find the treatment variables which affect the outcome, two types of multivariate analysis are done. Firstly, a determination of which variables are important is made: from age, gender, stage, histology, total dose, overall time, etc. Secondly, a quasi-biological model may be set up which includes those variables, e.g. Function (p) = Variable 1 + Variable 2 + ... + alpha x dose + beta x dose x (dose per fraction) - gamma x (overall time) where p is the probability of local control and "Function" is a logit or double-log function. The coefficients thus determined are often presented simply in raw form, or as ratios such as alpha/beta or gamma/alpha where any conversion factors from "Function (p)" to percentages are assumed conveniently to cancel out. However, it is mathematically possible to convert each coefficient directly into "percent change in local control per unit dose" (for alpha), or "percent per unit time" (for gamma), without recourse to the obvious convenience of the ratios. These converted values are more understandable than the coefficients themselves. They mean the rate of change of local control with (for example) total dose if overall time and dose per fraction were held constant; or rate of loss of local control with prolongation if total dose and dose per fraction were held constant. Even though heterogeneity may alter these slopes considerably from the theoretically maximum Poisson slopes, they still tell us what is happening averaged over the group of patients being studied, with often interesting insights.

Dose-Response Relationship, Radiation↗
PubMed2002

Assessment of lifestyle effects on the overall antioxidant capacity of healthy subjects.

Oxidative damage is increasingly recognized as playing an important role in the pathogenesis of several diseases such as cancer and cardiovascular diseases. Using a biologic test based on whole blood resistance to free-radical aggression, we sought to evaluate lifestyle factors that may contribute to the normal variability of the overall antioxidant status. We assessed this global antiradical defense capacity in 88 men and 96 women in relation to information on lifestyle obtained by questionnaire. In our relatively young, healthy population, we found a weak negative relation between male sex or aging and the resistance to oxidant stress. Among the factors studied, nonsmoking, vitamin and/or mineral supplementation, and regular physical activity were closely associated with an increased overall antioxidant capacity. Conversely, the antioxidant potential was negatively related to tobacco smoking; psychologic stress; alcohol consumption; moderate vegetable, low fruit, and low fish consumption; and, to a lesser extent, high natural ultraviolet light exposure. Thus, we were able to determine "unhealthy" and "healthy" lifestyle patterns that truly contributed to the variation of individual antioxidant capacity. We conclude that lifestyle determinants of cancer and cardiovascular risks were associated with a decreased overall antioxidant status as dynamically measured by means of a biologic test. Thus, the evaluation of the total human resistance against free-radical aggression, taking into account nutritional habits, lifestyle, and environmental factors, may be useful in preventive medicine as a precocious diagnosis to identify healthy subjects who are at risk for free-radical-mediated diseases.

Adult↗
PubMed2006

Significance of experts' overall ratings for medical student competence in relation to history-taking.

CONTEXT AND OBJECTIVE: Overall ratings (ORs) of competence, given by expert physicians, are increasingly used in clinical skills assessments. Nevertheless, the influence of specific components of competence on ORs is incompletely understood. The aim here was to investigate whether ORs for medical student history-taking competence are influenced by performance relating to communication skills, completeness of questioning and asking contentdriven key questions. DESIGN AND SETTING: Descriptive, quantitative study at Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo. METHODS: Thirty-six medical students were examined in a 15-station high-stake objective structured clinical examination (OSCE). At four stations devoted to history-taking, examiners filled out checklists covering the components investigated and independently rated students overall performance using a five-point scale from 1 (poor) to 5 (excellent). Physician ratings were aggregated for each student. Nonparametric correlations were made between ORs. RESULTS: ORs presented significant correlations with checklist scores (Spearmans rs = 0.38; p = 0.02) and OSCE general results (rs = 0.52; p < 0.001). Scores for "communication skills" tended to correlate with ORs (rs = 0.31), but without reaching significance (p = 0.06). Neither the scores for "completeness" (rs = 0.26; p = 0.11) nor those for "asking key questions" (rs = 0.07; p = 0.60) correlated with ORs. CONCLUSIONS: Experts overall ratings for medical student competence regarding history-taking is likely to encompass a particular dimension, since ratings were only weakly influenced by specific components of performance.

Adult↗
PubMed1976

Elicited responding to signals for reinforcement: the effects of overall versus local changes in reinforcement probability.

Pigeons were studied on a three-component multiple schedule where all reinforcement was independent of responding. Two components were cued by different keylights and were associated with different rates of reinforcement. The third was always a no-key period associated with extinction. After a few sessions, pecking was elicited by the keylights signalling the reinforcement and continued to be maintained indefinitely. The duration and sequence of the three components were varied to determine if the primary controlling variable was differences in the overall probability of reinforcement, or if it was the immediate change in reinforcement signalled by the onset and/or offset of the stimulus. Both variables were found to control behavior. When 30-sec components were used, the primary controlling variable was the overall probability of reinforcement, but when 3-min components were used, overall probability had little effect. Control by local changes in reinforcement also occurred, although the type of local control varied both across subjects and experimental conditions. Some behaviors were controlled more by the change in reinforcement signalled by the onset of the stimulus, while others were controlled more by the change signalled by the offset of the stimulus.

Journal Article↗
PubMed1996

Concurrent choice: Effects of overall reinforcer rate and the temporal distribution of reinforcers.

Six pigeons responded on a series of concurrent exponential variable-interval schedules, offering a within-subject comparison with previously published data from concurrent arithmetic variable-interval schedules. Both relative and overall reinforcer rates were varied between conditions. The generalized matching law described the data well, with undermatching much more frequent than strict matching. Time-allocation sensitivity consistently exceeded response-allocation sensitivity for both schedule types, and exponential-schedule sensitivity exceeded arithmetic-schedule sensitivity for both measures of choice. A further set of conditions using variable-interval schedules whose shortest interval was correlated with the mean interval, like arithmetic schedules, but that provided a constant conditional probability of reinforcement, like exponential schedules, produced sensitivities between those produced by conventional arithmetic and exponential schedules. Unlike previous arithmetic-schedule results, exponential sensitivity changed nonmonotonically with changes in overall reinforcer rate. The results clarify our knowledge of the effects of arithmetic and exponential schedules but confuse our understanding of the effects of overall reinforcer rate on concurrent choice.

Journal Article↗
PubMed1998

Humans' choice in a self-control choice situation: sensitivity to reinforcer amount, reinforcer delay, and overall reinforcement density.

Human subjects were exposed to a concurrent-chains schedule in which reinforcer amounts, delays, or both were varied in the terminal links, and consummatory responses were required to receive points that were later exchangeable for money. Two independent variable-interval 30-s schedules were in effect during the initial links, and delay periods were defined by fixed-time schedules. In Experiment 1, subjects were exposed to three different pairs of reinforcer amounts and delays, and sensitivity to reinforcer amount and delay was determined based on the generalized matching law. The relative responding (choice) of most subjects was more sensitive to reinforcer amount than to reinforcer delay. In Experiment 2, subjects chose between immediate smaller reinforcers and delayed larger reinforcers in five conditions with and without timeout periods that followed a shorter delay, in which reinforcer amounts and delays were combined to make different predictions based on local reinforcement density (i.e., points per delay) or overall reinforcement density (i.e., points per total time). In most conditions, subjects' choices were qualitatively in accord with the predictions from the overall reinforcement density calculated by the ratio of reinforcer amount and total time. Therefore, the overall reinforcement density appears to influence the preference of humans in the present self-control choice situation.

Adolescent↗