The testing of disinfectants

Although all disinfectant tests have the same final purpose, namely measuring the antimicrobial activity of a chemical substance or preparation, a large number of testing methods has been described. They are subdivided into suspension tests, carrier and surface disinfection tests and other practice-mimicking tests. The suspension tests comprise qualitative and quantitative suspension tests, and, as derived tests, the determination of the phenol coefficient and capacity tests. There is an essential difference between a carrier test and a surface disinfectant test: in the former case the carrier is submerged in the disinfectant solution during the whole exposure time, whereas in the latter case the disinfectant is applied on the carrier for the application time and thereafter the carrier is drying during the exposure.The basic principle now widely accepted is that the antimicrobial efficiency of a disinfectant is examined at three stages of testing.The first stage concerns laboratory tests in which it is verified whether a chemical compound or a preparation possesses antimicrobial activity. For these preliminary screening tests, suspension tests are considered.In the second stage of tests, disinfection procedures and not disinfectants are examined. It is determined under which conditions and at which use-dilution for a given application the preparation is active: the tests simulate real-life situations; such tests are carrier tests for the disinfection of materials by submersion and surface disinfection tests.The last stage takes place in the field, and comprises the in-loco or in-situ tests with as variants the in-use tests, which examine whether, after a normal period of use, germs are still killed by the disinfectant solution.It is the task of the European and international standardization organisations to develop new standards and to elaborate tests, which predict the effectiveness of a preparation in practice under variable circumstances.     

Testing Differentiation in Diploid Populations

We examine the power of different exact tests of differentiation for diploid populations. Since there is not necessarily random mating within populations, the appropriate hypothesis to construct exact tests is that of independent sampling of genotypes. There are two categories of tests, F(ST)-estimator tests and goodness of fit tests. In this latter category, we distinguish ``allelic statistics', which account for the nature of alleles within genotypes, from ``genotypic statistics' that do not. We show that the power of F(ST)-estimator tests and of allelic goodness of fit tests are similar when sampling is balanced, and higher than the power of genotypic goodness of fit tests. When sampling is unbalanced, the most powerful tests are shown to belong to the allelic goodness of fit group.     

Split support and split conflict randomization tests in phylogenetic inference

Randomization tests allow the formulation and statistical testing of null hypotheses about the quality of entire data sets or the quality of fit between the data and particular phylogenetic hypotheses. Randomization tests of phylogenetic hypotheses based on the concepts of split support and split conflict are described here, as are tests where splits, rather than the data, are randomly permuted. These tree-independent randomization tests are explored through their application to phylogenetic data for caecilian amphibians. Of these tests, split support randomization tests appear to be the most promising tools for phylogeneticists. These tests seem quite conservative, are applicable to nonpolar data and unordered multistate characters, and do not have the problems of nonindependence that affect split conflict and hierarchy tests. Unlike split conflict tests, their power does not appear to be correlated with split size. However, all tests are sensitive to taxonomic scope. Split support tests may help discern data that are likely to be affected by the problems of long-branches effects. Comparison of test results for mutually incompatible splits may help identify the presence of strong misleading signals in phylogenetic data. Significant split support could be a prerequisite for considering phylogenetic hypotheses to be well supported by the data, and split support randomization tests might be usefully applied prior to or as part of tree construction.     

Effects of severe prior exercise on assessment of maximal oxygen uptake

Five moderately fit males (50.8 ml.kg-1.min-1) performed 14 continuous type VO2 max tests on a motor-driven treadmill. Randomly assigned experimental sessions, consisting of three tests each and separated by 10 (tests 1, 2, 3), 20 (tests 4, 5, 6), 30 (tests 7, 8, 9), or 40 (tests 10, 11, 12) min, were conducted at a consistent hour for each subject every 4th day. Two separately performed tests were also included in the random assignment with the test eliciting the highest VO2 max value designated as the standard reference (SR). VO2 max values for tests 1 through 12 were not significantly different from the SR in spite of elevated pretest blood lactate concentrations ranging from 5 mM to 16 mM. Performance time was reduced for all tests other than tests 1, 4, 7, and 10, reaching the level of statistical significance (P less than 0.05) in tests 2, 3, 5, 6, and 9. It was concluded that valid and reliable assessment of VO2 max is possible even though testing is initiated with subjects in varying stages of exhaustion.     

Avoiding erroneously high levels of detection in combinations of semi-independent tests

A randomization procedure is proposed which allows statistical tests to be combined into a single test to maintain specified and acceptable levels of false detection. This method was applied to the problem of detecting density dependence in 135 unpublished time-series (of 10 generations) from insect populations, and to simulated density-dependent and density-independent data, so that the correctness of observed levels of detection from the published data could be verified. To allow the application of the randomization procedure to Bulmer's (1975) tests and Varley and Gradwell's (1960) test, these were recast as randomization tests. The randomization procedure was tested with 39 combinations of tests for density dependence (and limitation/attraction); it generally producedcombined tests with levels of detection that were intermediate between detection levels of the constituent tests (and hence was limite by these). The specified rate of false detection (5%) was never exceeded (by more than 1%) when combined tests were applied to time-series from a random-walk model. Two different combinations of tests produced levels of detection from the published time-series which were slightly greater than their constituent tests when they were combined into single tests. These were the randomized form of Bulmer's (1975) first test with the tests of Pollard et al. (1987) and Reddingius and den Boer (1989) with the randomized form of Bulmer's second test. The combination of Bulmer's first and Pollard et al.'s test produced a greater level of detection (21.5%) than any other single test or combination of tests. These results were confirmed by the analysis of modelled density dependent data. Although the increase in power of combinations of tests over single tests is small with the data we used, the combined tests (listed above) had rates of detection that were less influenced by the form of data (of two forms of density-dependent data) than were their constituent tests. Hence, it appears that the combined tests are of greater generality than single test statistics. The method presented here for combining several statistical tests into a single randomization test is applicable in many other areas of ecology where we wish to apply several tests and take the most probable result of these; and if the tests being conducted are, or can be expressed as, randomization tests.     

Survival Tests for r Groups

In this paper we give the generalization of the score tests covering the case of ties and we give examples where the expressions in matrix form are completely specified for the weighted tests and the score tests for the case of r groups. It is worth mentioning that although the score tests are not generally included in the commercial software, these tests should be used if it can be assumed that the censoring mechanism is equal in the r groups or if there is no censoring (Lawless , 1982). We establish the equivalence between “numerators” of these families of tests. As result of this equivalence we define four new tests that complete the classification of score and weighted tests. The Kruskal‐Wallis test (1952) appears as a particular case of the score tests for the case of non‐censoring. A simulation study has been done in order to compare the performance of the tests described in this paper. An example is included to make the understanding of the paper easier.     

Bayesian approaches to modeling the conditional dependence between multiple diagnostic tests

Many analyses of results from multiple diagnostic tests assume the tests are statistically independent conditional on the true disease status of the subject. This assumption may be violated in practice, especially in situations where none of the tests is a perfectly accurate gold standard. Classical inference for models accounting for the conditional dependence between tests requires that results from at least four different tests be used in order to obtain an identifiable solution, but it is not always feasible to have results from this many tests. We use a Bayesian approach to draw inferences about the disease prevalence and test properties while adjusting for the possibility of conditional dependence between tests, particularly when we have only two tests. We propose both fixed and random effects models. Since with fewer than four tests the problem is nonidentifiable, the posterior distributions are strongly dependent on the prior information about the test properties and the disease prevalence, even with large sample sizes. If the degree of correlation between the tests is known a priori with high precision, then our methods adjust for the dependence between the tests. Otherwise, our methods provide adjusted inferences that incorporate all of the uncertainty inherent in the problem, typically resulting in wider interval estimates. We illustrate our methods using data from a study on the prevalence of Strongyloides infection among Cambodian refugees to Canada.     

Multi-Biochemical Test System for Distinguishing Enteric and Other Gram-Negative Bacilli

A multi-biochemical test system consisting of nine tests, entitled Enterotube, was evaluated in parallel with conventional tests to determine its value in the identification of enteric and certain other gram-negative bacilli. The 242 bacterial strains studied were from a variety of pathological specimens and from our culture collection. When the results with individual tests represented in both test systems were compared, no discrepancies were noted in the indole test, and one discrepancy was recorded for dextrose. In 7 of 242 hydrogen sulfide tests, 3 of 242 phenylalanine tests, 22 of 242 urease tests, 15 of 242 dulcitol tests, 12 of 242 lactose tests, 27 of 217 lysine decarboxylase tests, and 5 of 242 citrate tests, the Enterotube results were contrary to those obtained with conventional methods. The lysine decarboxylase test in the Enterotube posed a problem of interpretation and readability and is not an acceptable alternative to the conventional methods. Fifteen of the strains studied were incorrectly identified by the Enterotube system and four could not be differentiated from other closely related strains. Salmonella could be identified as to group, whereas Shigella strains were frequently misidentified as Escherichia. The Enterotube method is simple and convenient, and all media are inoculated at once from a single colony.     

Statistical tests of neutrality in the age of weak selection

Why review statistical tests of neutrality at a time when pan-selectionists and pan-neutralists alike seem to have been replaced by weak selectionists? First, we still don't actually know how variation is maintained at the molecular level; and second, tests of neutrality have a utility for evolutionary biologists beyond the neutralist/selectionist debate. New tests and variations on the existing tests are arising practically every month. From the complementary viewpoints of an empiricist and a theoretician, we sample the recent literature on tests of statistical neutrality and discuss the motivations, applications, assumptions, interpretations and future directions of these tests.     

Memory tests in healthy elderly: age factors and norms

The study aimed to assess the strength of age effects on both standard laboratory and ecological memory tests and the psychometric qualities of these tests. Furthermore, norm data are constructed. Memory performance was assessed in a random group of older adults (mean age 62 years, range 46-89) and a group of older adults having memory complaints who applied for memory training (mean age 63 years, range 45-85). Age effects were found on almost all memory tests, whether artificial laboratory or more ecological tests were used. Age effects remained generally present after correction for educational level. Retest reliabilities of the ecological memory tests did not differ systematically from those of standard laboratory tests. However, not all tests showed satisfactory retest reliabilities, this was even true for tests often used in clinical settings. For tests with retest reliabilities above r = .65 norms corrected for age and educational level were provided. The group of older adults having memory complaints performed on average better than the random group of older adults from the population. In the first group, higher performance thresholds should be employed in assessing whether memory performance is deviant.     

Wald Tests of Location for Symmetric Nonnormal Data

For nonnormal data we suggest a test of location based on a broader family of distributions than normality. Such a test will in a sense fall between the standard parametric and non parametric tests. We see that the Wald tests based on this family of distributions have some advantages over the score tests and that they perform well in comparison to standard parametric and nonparametric tests in a variety of situations. We also consider when and how to apply such tests in practice.     

Genioglossus and breathing responses to airway occlusion: effect of sleep and route of occlusion

We examined the effect of sleep state on the response of genioglossus muscle (EMGgg) activity to total airway occlusion applied at 1) nasal (N) airway [and thus exposing the upper airway (UAW) to pressure changes] and 2) tracheal (T) airway (thus excluding UAW from pressure changes). A total of 233 tests were performed during wakefulness (W), 98 tests in slow-wave sleep (SWS), and 72 tests in rapid-eye-movement (REM) sleep. Prolongation of inspiratory time (TI) of the first occluded effort occurred in all tests irrespective of behavioral state, with the greatest increase seen in awake N tests. Nasal tests augmented EMGgg activity in the first occluded breath and produced a linear increase in EMGgg during occlusion. The EMGgg activity at any given time during nasal occlusion in SWS was less than that recorded during W tests. There was a marked reduction in EMGgg response to N occlusion during REM sleep. The EMGgg activity during awake T tests was significantly less than that of N tests at any given time during occlusion. There was no relationship between the level of EMGgg activity and asphyxia in T tests performed during SWS and REM sleep. Nasal tests decreased the force generated by the inspiratory pump muscles and the central drive to breathing compared with T tests. These results confirm the important role of the UAW in regulating breathing pattern and indicate that both immediate and progressive load-compensating responses during nasal occlusion are influenced by information arising from the UAW.     

Correlations among assays of porcine semen quality following cryopreservation

Correlations between in vitro tests of semen quality, used to predict the in vivo fertilizing potential of sperm, indicate that the tests may substitute for each other in predicting fertilizing potential. Lack of correlation between tests suggest that both tests should be used to estimate the fertilizing potential. The purpose of this study was to establish correlations between several in vitro tests of porcine semen quality following freezing. Tests of motility with and without caffeine, spermatozoa with normal apical ridges, sephadex filtration with and without caffeine and acrosin activity were all correlated with each other. Correlations among these tests ranged from 0.45 to 0.83 (P<0.05). Assays for glutamic oxalacetic transaninase (GOT) were not consistently correlated with other tests. None of these tests of semen quality were correlated with the sperm penetration assay except for the test of motility without caffeine, which was correlated with the number of penetrations per hamster oocyte (r = 0.71, P<0.05).     

A Clinical Comparison Between the Friedman Test and an in Vitro Test for Pregnancy

Latex pregnancy tests were performed on 737 urine samples submitted to a hospital laboratory for Friedman tests. Clinical confirmation of the diagnoses was obtained in 666. Nine Friedman and 31 latex tests were falsely positive in 199 samples having specific gravities over 1.015. Each test gave four false-positive results in 65 samples with specific gravities under 1.015. Between six and 13 weeks of gestation, nine Friedman and 45 latex tests were negative in 176 samples with specific gravities above 1.015; below 1.015, five Friedman and 15 latex tests were false in 42 samples. At other stages of pregnancy, seven Friedman and 18 latex tests were negative in 56 samples with specific gravities over 1.015 and, under 1.015, nine samples had four negative latex tests.The latex test requires careful control and is less reliable than the Friedman test.     

Toxicity tests with Daphnids: Its application in the management of water quality

The possible role of Daphnia species in toxicity tests is discussed. In screening tests, effluent monitoring tests and legal tests daphnids are recommended as useful test organisms. They also may help to establish concentration limits for chemical water pollution (water quality criteria). As biological indicator organisms their use is limited.     

Biochemical tests for identification of mycelial cultures of basidiomycetes

Twenty-four biochemical tests have been developed to identify basidiomycetes from mycelial cultures. Eleven are designated ‘instant tests’ because results are obtained within 24 h; ten of these test for specific enzymes, the other is based on a reaction between vanillin and unknown fungal metabolites. The remaining thirteen tests require incubation periods ranging from 1 to 4 days and are thus designated ‘incubated tests’. Sixteen of these tests were applied first to identified isolates of Peniophora sacrata, Sclerotium rolfsii, Stereum purpureum and Trametes versicolor. They distinguished these species satisfactorily, so these sixteen tests, and eight others devised subsequently, were applied to unidentified basidiomycetes isolated from diseased roots of fruit crops. The results of these tests enabled the isolates to be placed in seven groups. All isolates in a particular group were morphologically similar which further suggested that each group might correspond to a species and that isolates could be defined on the basis of biochemical tests.     

The identification of diphtheria, tetanus and pertussis vaccines by single radial and double immunodiffusion techniques

The identification tests for adsorbed diphtheria, tetanus and pertussis vaccines, which are required by the European Pharmacopoeia to be undertaken in animals, may be replaced by precipitation tests, for instance in agaros gels. Such in vitro tests eliminate the use of animals and are less expensive and time-consuming. The single radial immunodiffusion technique is a suitable semiquantitative test, while the double diffusion test is necessary for the investigation of complete or partial identity. The precipitates obtained in the single radial diffusion tests and in double diffusion tests with diphtheria toxoid were visible without staining; those obtained in the double diffusion tests with tetanus toxoid were weaker and staining was sometimes needed.     

Limitations of immunofluorescence tests in the diagnosis of infectious mononucleosis

The relative value of heterophil agglutinins (HA) and of specific EBV antibodies in the diagnosis of infectious mononucleosis (IM) was assessed in 108 cases of the disease and in 280 controls. Among the 108 cases 93 were HA-positive by sheep cells in at least one of their sera, while 15 were HA-negative by the same test. Among the 280 controls false-positive HA tests were not encountered except in eight cases with the horse cell microtitre tests. With one of the two slide tests at least two false-positive tests and 12 false-negative tests were also found but these sera had low titres in microtitre tests. The HA life-span was found to be unexpectedly long in a few cases, sheep cell HA lasting up to 8 to 10 months and horse cell HA up to 21 to 23 months.Many false-positive tests may therefore not be true false-positives and may result from the persistence of HA following unrecognized mononucleosis months before. Virtually all cases of IM had (or developed) antibodies to Epstein-Barr virus, viral capsid antigen (EBV-VCA), whereas only half of the controls were EBV-VCA-positive. The comparative analysis of nonspecific and specific test results in mononucleosis allows the following conclusions: (1) horse cell microtitre tests and the monospot test are more sensitive than sheep cell microtitre tests and the monotest; (2) false-negative results are occasionally seen with the latter tests but not with the former; (3) more false-positive results, however, are probably seen with the former tests; and (4) specific EBV-IgM and EBV-EA antibody tests are useful in the diagnosis of selected borderline cases of mononucleosis.     

Tests of the mouse visual system

To apply the approach of forward genetics (e.g., gene identification with mutagenesis and screening, followed by positional cloning) to the mouse, it is necessary to have available screening tests that can be applied rapidly to individual mice and that give a reliable assessment of visual function. This paper reviews the strengths and limitations of two anatomical tests related to visual function, fundus examination and retinal histological examination. Two tests that do not depend on behavior of a conscious animal are reviewed: the electroretinogram and the visual evoked potentials of the cortex. Eight behavioral tests are also summarized: maze-based tests, cued fear conditioning, tests based on conditioned suppression, visual placing, optokinetic nystagmus, pupillary reflex, and light-induced shifts in circadian phase. It is recommended that retinal histology, the electroretinogram, and visual-evoked potentials be used at the present time for screening because they assess the function and structure of the visual system rapidly and reliably. In fact, the electroretinogram (or visually evoked potentials) can be recorded from several animals simultaneously in response to the same stimulus. It is also recommended that efforts be made to develop more appropriate, automated, behavioral tests of visual perception than are now available, particularly tests that rely solely on rewarding visually evoked behavior. Two other promising behavioral tests are cued fear conditioning and variants of maze tests. Received: 17 December 1999 / Accepted: 17 December 1999