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PubMed1990

Introduction to biostatistics: Part 3, Sensitivity, specificity, predictive value, and hypothesis testing.

Diagnostic tests guide physicians in assessment of clinical disease states, just as statistical tests guide scientists in the testing of scientific hypotheses. Sensitivity and specificity are properties of diagnostic tests and are not predictive of disease in individual patients. Positive and negative predictive values are predictive of disease in patients and are dependent on both the diagnostic test used and the prevalence of disease in the population studied. These concepts are best illustrated by study of a two by two table of possible outcomes of testing, which shows that diagnostic tests may lead to correct or erroneous clinical conclusions. In a similar manner, hypothesis testing may or may not yield correct conclusions. A two by two table of possible outcomes shows that two types of errors in hypothesis testing are possible. One can falsely conclude that a significant difference exists between groups (type I error). The probability of a type I error is alpha. One can falsely conclude that no difference exists between groups (type II error). The probability of a type II error is beta. The consequence and probability of these errors depend on the nature of the research study. Statistical power indicates the ability of a research study to detect a significant difference between populations, when a significant difference truly exists. Power equals 1-beta. Because hypothesis testing yields "yes" or "no" answers, confidence intervals can be calculated to complement the results of hypothesis testing. Finally, just as some abnormal laboratory values can be ignored clinically, some statistical differences may not be relevant clinically.

Biometry↗
PubMed1991

Hypothesis-testing abilities of language-impaired children.

Hypothesis-testing abilities were assessed using a modification of the discrimination-learning paradigm employed by Nelson, Kamhi, and Apel (1987) that was designed to minimize the short-term memory demands of the task. Sixteen language-impaired and 16 normal-language children in kindergarten and first and second grades participated in the study. The language-impaired children solved significantly fewer problems than normal-language controls equated on cognitive level, but the two groups used similar hypothesis types to solve the problems. Type of verbal feedback provided during the hypothesis testing task (explicit vs. nonexplicit) did not significantly affect the performance of either group. These results are interpreted as indicating that language-impaired children demonstrate inefficient use of problem-solving strategies that cannot be attributed solely to memory difficulties. Issues surrounding the investigation of language-impaired children's cognitive abilities are discussed.

Child↗
PubMed1990

Ventricular tachycardia and fibrillation detection by a sequential hypothesis testing algorithm.

An algorithm for detecting ventricular fibrillation (VF) and ventricular tachycardia (VT) by the method of sequential hypothesis testing is presented. The algorithm first generates a binary sequence by comparing the signal to a threshold. The probability distribution of the time intervals of the binary sequence is obtained, and Wald's sequential hypothesis testing procedure is next employed to discriminate the arrhythmias. Sequential hypothesis testing of 85 cases resulted in identification of 1) 97.64% VF and 97.65% VT episodes after 5 s, and 2) 100% identification of both VF and VT after 7 s. The desired false positive and false negative error probabilities can be preprogrammed into the algorithm. An important feature of the sequential method is that extra time for detection can be traded off for improved accuracy, and vice versa.

Algorithms↗
PubMed1976

Familial aggregation of chronic respiratory disease: use of National Health Interview Survey data for specific hypothesis testing.

The 1970 National Health Interview Survey included questions on respiratory disease and smoking habits. The new data were released in July 1974. Data consisted of information on approximately 116,000 persons from 37,000 households selected randomly from 357 primary sampling units. To test a hypothesis about familial clustering of chronic respiratory disease in households, we selected as index households those having an adult (aged 35-54 years) reporting a diagnosis of asthma, bronchitis, or emphysema and also having first order relatiaves less than age 35. Index households were matched with households from the same neighbourhood having an adult aged 35-54, of the same sex as the diseased person in the index household, without disease and with all other adults 35-54 without disease, and which had first order relatives less than 35 living in the same household. Analysis was carried out using Cochran's d-test to compare frequency of respiratory disease in persons less than 35 in each group. There was a strong association (P less than .001) between persons over 35 with chronic respiratory diseases and the disease rate in their first order relatives. The association could not be explained by differences in demographic variables and smoking habits.

Adolescent↗
PubMed1979

The effects of introtacts on hypothesis testing in kindergarten and first-grade children.

Kindergarten and first-grade children were trained against their initial dimensional preference in a 2-dimensional simultaneous discrimination learning task. One third of the children received pretraining in using a sequential hypothesis-testing strategy, one third received pretraining in which they experienced solutions to tasks of the same type, and one third received no pretraining. Half of the children received introtact probes prior to each trial in the criterion task. Introtact probes had no effect on the performance of kindergarten children but facilitated the performance of first-grade children who received pretraining. Performance was generally better in the pretraining conditions than in the control condition and was generally better for first graders than for kindergarten children. Indices of the use of the sequential hypothesis-testing strategy were obtained from the responses to introtact probes. 75% of the first graders who received pretraining in hypothesis testing showed high proficiency in using the strategy, whereas only 38% of the kindergarten children did so. A strong tendency to become fixated on the irrelevant dimension was evident at both age levels.

Child↗
PubMed1992

Information selection and use in hypothesis testing: what is a good question, and what is a good answer?

The process of hypothesis testing entails both information selection (asking questions) and information use (drawing inferences from the answers to those questions). We demonstrate that although subjects may be sensitive to diagnosticity in choosing which questions to ask, they are insufficiently sensitive to the fact that different answers to the same question can have very different diagnosticities. This can lead subjects to overestimate or underestimate the information in the answers they receive. This phenomenon is demonstrated in two experiments using different kinds of inferences (category membership of individuals and composition of sampled populations). In combination with certain information-gathering tendencies, demonstrated in a third experiment, insensitivity to answer diagnosticity can contribute to a tendency toward preservation of the initial hypothesis. Results such as these illustrate the importance of viewing hypothesis-testing behavior as an interactive, multistage process that includes selecting questions, interpreting data, and drawing inferences.

Adult↗
PubMed1990

Introduction to biostatistics: Part 5, Statistical inference techniques for hypothesis testing with nonparametric data.

Specific statistical tests are used when the null hypothesis (H0) is to be tested using nonparametric nominal or ordinal data. With nominal data, experimental results are expressed by proportions or frequencies. Chi-square or related tests (the Fisher's exact test or the rows by columns test) are appropriate for testing H0 with nominal data. Ordinal data permit arrangement of statistical results by rank. Rank-order tests used to test H0 with ordinal data include the Mann-Whitney U, Kolmogorov-Smirnov, Wilcoxon, Kruskal-Wallis, and Friedman tests. The Kruskal-Wallis and Friedman tests permit multiple intergroup comparisons. Other rank-order tests permit only single intergroup comparisons. Specific details to guide the researcher in the proper selection of these tests are presented.

Statistics as Topic↗
PubMed1976

The psychiatric examination in the walk-in clinic. Hypothesis generation and hypothesis testing.

Rapid assessment for decision making is a major goal of the initial psychiatric interview in walk-in clinics, emergency psychiatric services, and the ambulatory services of community mental health centers. To accomplish this task, the clinician must learn to elicit specific data to confirm or refute clinical hypotheses rather than gather a complete history. This report, in formulating a hypothesis generating and testing approach for the initial psychiatric examination, proposes 16 hypotheses that organize the clinical data necessary for most decisions. This approach is intended to help the clinician make efficient use of limited time, guard him from coming to premature closure in the collection of data, and provide a stimulus for the exploration of relevant but neglected clinical questions.

Affective Symptoms↗
PubMed1976

An assessment of hypothesis testing in mentally retarded adolescents.

Groups of educable and trainable institutionalised retarded adolescents were tested on a discrimination learning problem with a modified blank trials procedure in an attempt to measure their hierarchy of hypotheses. Results indicated that the hierarchy and size of initial hypothesis sets varied as a function of degree of retardation. Trainable retarded subjects had fewer hypotheses, and initially chose position hypotheses predominantly. Under discriminate reinforcement, most of these were readily switched to stimulus dimension hypotheses, which they retained during additional non-discriminate (100 per cent) reinforcement trials. Educable retarded subjects predominantly chose stimulus dimension hypotheses initially, and most of these switched to position hypotheses during either discriminate or non-discriminate reinforcement trials.

Adolescent↗
PubMed1990

Statistical significance and statistical power in hypothesis testing.

Experimental design requires estimation of the sample size required to produce a meaningful conclusion. Often, experimental results are performed with sample sizes which are inappropriate to adequately support the conclusions made. In this paper, two factors which are involved in sample size estimation are detailed--namely type I (alpha) and type II (beta) error. Type I error can be considered a "false positive" result while type II error can be considered a "false negative" result. Obviously, both types of error should be avoided. The choice of values for alpha and beta is based on an investigator's understanding of the experimental system, not on arbitrary statistical rules. Examples relating to the choice of alpha and beta are presented, along with a series of suggestions for use in experimental design.

Research Design↗
PubMed1992

Evaluation of hypothesis testing for comparing two populations using NONMEM analysis.

In a simulation study of inference on population pharmacokinetic parameters, two methods of performing tests of hypotheses comparing two populations using NONMEM were evaluated. These two methods are the test based upon 95% confidence intervals and the likelihood ratio test. Data were simulated according to a monoexponential model and, in that context, power curves for each test were generated for (i) the ratio of mean clearance and (ii) the ratio of the population standard deviations of clearance. To generate the power curves, a range of these parameters was employed; other pharmacokinetic parameters were selected to reflect the variability typically present in a Phase II clinical trial. For tests comparing the means, the confidence interval tests had approximately the same power as the likelihood ratio tests and were consistently more faithful to the nominal level of significance. For comparison of the standard deviations, and when the volume of information available was relatively small, however, the likelihood ratio test was more able to detect differences between the two groups. These results were then compared to results on parameter estimation in order to gain insight into the question of power. As an example, the nonnormality of estimates of the ratio of standard deviations plays an important role in explaining the low power for the confidence interval tests. We conclude that, except for the situation of modeling standard deviations with only sparse information, NONMEM produces tests of significance that are effective at detecting clinically significant differences between two populations.

Computer Simulation↗
PubMed1990

Evolutionary relationships between "Q-type" photosynthetic reaction centres: hypothesis-testing using parsimony.

Hypotheses concerning the evolutionary relationships between "Q-type" photosynthetic reaction centres are tested using amino acid parsimony analysis of subunit sequences and an alignment based on dot matrix comparisons. Strong evidence is found for independent gene duplications having produced the L and M subunits of the photosynthetic purple bacterial reaction centre and D1 and D2 of Photosystem-II. Much support is also found for the L and M subunits of the green filamentous bacterium Chloroflexus aurantiacus arising from the same gene duplication as the purple bacterial subunits, suggesting there was an ancestral bacterial heterodimeric reaction centre. These conclusions caution against over-extrapolation from the purple bacterial reaction centre to Photosystem-II, and suggest that the latter is more ancient than previously supposed.

Bacteria↗