Search PubMed⌕ Search

Biomedical subjects

H Shannon

Publications and source records attributed to H Shannon.

15 recordsLinked to original sources
PubMed1995

Basic statistics for clinicians: 4. Correlation and regression.

Correlation and regression help us to understand the relation between variables and to predict patients' status in regard to a particular variable of interest. Correlation examines the strength of the relation between two variables, neither of which is considered the variable one is trying to predict (the target variable). Regression analysis examines the ability of one or more factors, called independent variables, to predict a patient's status in regard to the target or dependent variable. Independent and dependent variables may be continuous (taking a wide range of values) or binary (dichotomous, yielding yes-or-no results). Regression models can be used to construct clinical prediction rules that help to guide clinical decisions. In considering regression and correlation, clinicians should pay more attention to the magnitude of the correlation or the predictive power of the regression than to whether the relation is statistically significant.

Data Interpretation, Statistical↗
PubMed1995

Basic statistics for clinicians: 3. Assessing the effects of treatment: measures of association.

In the third of a series of four articles the authors show the calculation of measures of association and discuss their usefulness in clinical decision making. From the rates of death or other "events" in experimental and control groups in a clinical trial, we can calculate the relative risk (RR) of the event after the experimental treatment, expressed as a percentage of the risk without such treatment. The absolute risk reduction (ARR) is the difference in the risk of an event between the groups. The relative risk reduction is the percentage of the baseline risk (the risk of an event in the control patients) removed as a result of therapy. The odds ratio (OR), which is the measure of choice in case-control studies, gives the ratio of the odds of an event in the experimental group to those in the control group. The OR and the RR provide limited information in reporting the results of prospective trials because they do not reflect changes in the baseline risk. The ARR and the number needed to treat, which tells the clinician how many patients need to be treated to prevent one event, reflect both the baseline risk and the relative risk reduction. If the timing of events is important--to determine whether treatment extends life, for example--survival curves are used to show when events occur over time.

Case-Control Studies↗
PubMed1995

Basic statistics for clinicians: 2. Interpreting study results: confidence intervals.

In the second of four articles, the authors discuss the "estimation" approach to interpreting study results. Whereas, in hypothesis testing, study results lead the reader to reject or accept a null hypothesis, in estimation the reader can assess whether a result is strong or weak, definitive or not. A confidence interval, based on the observed result and the size of the sample, is calculated. It provides a range of probabilities within which the true probability would lie 95% or 90% of the time, depending on the precision desired. It also provides a way of determining whether the sample is large enough to make the trial definitive. If the lower boundary of a confidence interval is above the threshold considered clinically significant, then the trial is positive and definitive, if the lower boundary is somewhat below the threshold, the trial is positive, but studies with larger samples are needed. Similarly, if the upper boundary of a confidence interval is below the threshold considered significant, the trial is negative and definitive. However, a negative result with a confidence interval that crosses the threshold means that trials with larger samples are needed to make a definitive determination of clinical importance.

Clinical Trials as Topic↗
PubMed1995

Basic statistics for clinicians: 1. Hypothesis testing.

In the first of a series of four articles the authors explain the statistical concepts of hypothesis testing and p values. In many clinical trials investigators test a null hypothesis that there is no difference between a new treatment and a placebo or between two treatments. The result of a single experiment will almost always show some difference between the experimental and the control groups. Is the difference due to chance, or is it large enough to reject the null hypothesis and conclude that there is a true difference in treatment effects? Statistical tests yield a p value: the probability that the experiment would show a difference as great or greater than that observed if the null hypothesis were true. By convention, p values of less than 0.05 are considered statistically significant, and investigators conclude that there is a real difference. However, the smaller the sample size, the greater the chance of erroneously concluding that the experimental treatment does not differ from the control--in statistical terms, the power of the test may be inadequate. Tests of several outcomes from one set of data may lead to an erroneous conclusion that an outcome is significant if the joint probability of the outcomes is not taken into account. Hypothesis testing has limitations, which will be discussed in the next article in the series.

Clinical Trials as Topic↗
PubMed1995

Effects of prehospital care on outcome in patients with cardiac illness.

STUDY OBJECTIVE: To compare outcomes of patients with acute cardiac illness transported by ambulance for whom prehospital care was provided by emergency medical technician-paramedics (EMT-Ps) or EMTs trained in defibrillation (EMT-Ds). DESIGN: A prospective chart review carried out over 3.5 years. SETTING: The Hamilton-Wentworth region of Ontario, Canada, which covers 1,136 km2 and includes five receiving hospitals. PARTICIPANTS: We prospectively identified 8,720 potentially eligible patients from approximately 30,000 who presented to the ambulance service. We reviewed hospital charts to confirm eligibility. The group of 8,720 patients yielded 3,066 patients with acute cardiac illness who met all other eligibility requirements. We excluded patients in cardiac arrest. RESULTS: Incidence of myocardial infarction (MI), length of hospital stay, and mortality were evaluated. Analysis was performed with chi 2 tests for association, linear regression, and logistic regression. Of the eligible patients who received prehospital EMS care, 783 sustained MIs. The proportions of people discharged alive with the diagnosis of MI did not differ between crew types (P = .16). Average hospital stay was 13 days in both groups for patients with the discharge diagnosis of MI; hospital stay ranged from 9 (EMT-D) to 11 days (EMT-P) for any patient with a discharge diagnosis other than MI. These values were statistically similar. The odds ratio of having had an MI after treatment by an EMT-D crew was 1.02 (95% confidence interval, .86 to 1.21) compared with that for treatment by an EMT-P crew. CONCLUSIONS: In an urban setting with short (less than 10 minutes) average transport times, the availability of prehospital paramedic care does not affect occurrence of MI, length of hospital stay, or mortality of patients presenting to the EMS system with cardiac illness.

Aged↗
PubMed1994

General pharmacology of gemcitabine hydrochloride in animals.

Gemcitabine (2',2'-difluorodeoxycytidine monohydrochloride, LY188011 hydrochloride, CAS 122111-03-9) is a nucleoside analog with a broad spectrum of antitumor activity in murine models and is currently undergoing clinical evaluation. The profile of the pharmacological effects of this agent was assessed in studies evaluating the cardiovascular and respiratory systems, renal function, the gastrointestinal system, the central nervous system, and the autonomic nervous system. In vivo doses ranged from 0.15 to 300 mg/kg given by the intravenous route, while in vitro concentrations up to 1 x 10-3 mol/l were used. Gemcitabine was inactive in the autonomic nervous system, gastrointestinal function, and central nervous system studies. Only minimal changes were seen in the cardiovascular and respiratory study, with a slight decrease in pulmonary arterial pressure at the mid dose and a stroke volume increase at the high dose. In the renal function studies, a slight decrease in the urine pH at the high dose and decreased serum creatinine at the mid dose levels were observed. In summary, gemcitabine had minimal effect in these pharmacodynamic studies. These results indicate that gemcitabine has a low potential to produce adverse pharmacologic effects.

Animals↗
PubMed1993

General pharmacology of loracarbef in animals.

Loracarbef ((6R, 7S)-7-[(R)-2-amino-2-phenyl-acetamido]-3-chloro-8-oxo-1- azabicyclo [4.2.0]oct-2-ene-2-carboxylic acid, monohydrate, LY 163892, CAS 121961-22-6) is a carbacephem antibiotic targeted for use in the treatment of infectious disease. The potential pharmacological effects of this agent were examined on cardiovascular, respiratory, gastrointestinal, central nervous and autonomic nervous systems. Also examined were local anesthetic activity, effects on platelet aggregation, circulating blood glucose, primary antibody production, renal function, blood coagulation, ocular irritation, and the acute inflammatory response. Doses of 100, 1000, and 2000 mg/kg given by the oral route were selected for most in vivo studies. Concentrations up to 3 x 10(-3) mol/l were used in vitro. Loracarbef was essentially inactive in the tests of central and autonomic nervous system function, platelet aggregation, renal function, blood hemolysis, primary antibody production, blood coagulation, and ocular irritation. It had no local anesthetic activity. At high oral or intravenous doses, representing significant multiples of the therapeutic dose, loracarbef caused changes in gastrointestinal (decrease in gastric acid production and gastric fluid volume; increased biliary output), cardiovascular (increased mean pressure, cardiac output, heart rate, and femoral flow), blood glucose (increased glucose levels), and anti-inflammatory tests (suppressed acute inflammatory response). In summary, loracarbef exhibited minimal activity in these pharmacodynamic studies. These results indicate loracarbef has a low potential to produce adverse effects at therapeutic doses.

Anesthetics, Local↗
PubMed1993

Characterization of enamel exposed to 10% carbamide peroxide bleaching agents.

The purpose of this investigation was to evaluate the effect of three 10% carbamide peroxide bleaching agents on enamel microhardness and surface morphology. Seventy-two enamel slabs were subjected to one of three carbamide peroxide solutions or an artificial saliva solution for 15 hours a day for 2- and 4-week periods. During the remaining 9 hours, slabs were exposed to human saliva in vivo. Although differences were not statistically significant, microhardness values of all treated specimens 2 weeks after treatment were less than those of control specimens. These trends, however, were not evident at 4 weeks. Scanning electron microscopic evaluation revealed significant surface alterations in enamel topography for slabs treated with the bleaching solutions for 4 weeks. The most severe alterations were found in slabs exposed to the lower-pH solutions.

Adult↗
PubMed1989

General pharmacology of nizatidine in animals.

Nizatidine (N-[2-[[[2-[(dimethylamino)methyl-4-thiazolyl]- methyl]thio]ethyl]-N'-methyl-2-nitro-1,1-ethenediamine, LY139037, Axid) is a novel, potent, and selective H2-antagonist. The potential secondary pharmacologic effects of this agent on the cardiovascular, respiratory, gastrointestinal, renal, hepatic, autonomic, and central nervous systems as well as effects on circulating blood glucose and the acute inflammatory response were examined. Nizatidine was generally inactive in the tests conducted in mice, rats, guinea pigs, rabbits, and dogs. Nizatidine and the reference H2-antagonist, cimetidine, both produced effects upon the cardiovascular and respiratory systems by intravenous administration in anesthetized dogs at doses in excess of the intended clinical exposure. In summary, these studies confirm the selective pharmacologic activity of nizatidine and indicate a low potential for secondary pharmacologic side effects to be encountered clinically.

Animals↗
PubMed1983

Sample size in occupational mortality studies.

In 1980, the Occupational Safety and Health Administration asserted that "non-positive human studies" would be considered in reviews of evidence only if in a study the "group of exposed subjects was large enough for an increase in cancer incidence of 50% above that in unexposed controls to have been detected at any of the predicted sites." The concepts of statistical testing and power in occupational mortality studies are reviewed, and studies published in two prominent occupational health journals in 1979 and 1980 are analyzed in terms of their power. A large proportion of standardized mortality ratio studies have a low probability of detection of relative risks of the order of 1.5.

Epidemiologic Methods↗
PubMed1980

Etiology of carcinoma of the larynx.

Since 1973, evidence based on case-control and mortality studies has suggested that carcinoma of the larynx was an asbestos-related tumour. In this study, 305 male and 206 female patients were interviewed on admission to the Royal National Throat Nose and Ear Hospitals in London. Following endoscopy, biopsy material was reviewed and classified as either neoplastic, cysts and polyps or inflammatory; a fourth group consisted of patients for whom the surgeon recorded that the larynx appeared normal on inspection and from whom no biopsy was taken. Only 15 neoplastic conditions were detected among the women, and only two had asbestos exposure; thus, no further analysis was made. Among the males, the neoplastic group was significantly older than the other groups, and cigarette smoking was significantly more common. Alcohol consumption did not differ significantly; and asbestos exposure was not more common in the neoplastic group than in the three other groups.

Adult↗
PubMed1975

An analysis of factors affecting survival in 150 patients with renal carcinoma.

A review of 150 patients with renal carcinoma revealed that 45 per cent were hospitalized with distant metastases or tumors that were unresectable. Although the behavior of the neoplasm in the 55 per cent who were theoretically curable was generally unpredictable, longevity and survival were markedly increased in patients with tumors less than 8 cm. in size and concomitantly with other acknowledged features of low stages of the disease. Since patients can survive with tumor for long periods and metastases may occur many years after the operation prognosis must be guarded and long followup is needed to assess the results of therapy at any stage of the disease.

Adolescent↗