A comparison of methods for estimating the lactate threshold

The purpose of this study was to examine the accuracy of tests that may be used by distance runners to estimate the lactate threshold. Competitive distance runners/triathletes (N = 27) performed a criterion test that directly measured (blood lactate of 4.0 mmol.L(-1)) the lactate threshold. Subjects then performed 4 tests (VDOT, 3,200-m time trial, 30-minute time trial, Conconi) that estimate the threshold. Mean estimations of the running velocity at the lactate threshold from the 30-minute time trial (standard error of the estimate, SEE, 0.21 m.s(-1)) and VDOT (SEE 0.41 m.s(-1)) methods did not differ (P>0.05) from the criterion. In terms of heart rate, the 30-minute time trial estimation did not significantly differ (SEE 8.0 b.min(-1)) from criterion. These findings suggest that the 30-minute time-trial method should be considered by coaches and distance runners/triathletes as a method for estimating both the running velocity and heart rate at the lactate threshold.     

A comparison of methods for adaptive treatment selection

Traditionally drug development is generally divided into three phases which have different aims and objectives. Recently so-called adaptive seamless designs that allow combination of the objectives of different development phases into a single trial have gained much interest. Adaptive trials combining treatment selection typical for Phase II and confirmation of efficacy as in Phase III are referred to as adaptive seamless Phase II/III designs and are considered in this paper. We compared four methods for adaptive treatment selection, namely the classical Dunnett test, an adaptive version of the Dunnett test based on the conditional error approach, the combination test approach, and an approach within the classical group-sequential framework. The latter two approaches have only recently been published. In a simulation study we found that no one method dominates the others in terms of power apart from the adaptive Dunnett test that dominates the classical Dunnett by construction. Furthermore, scenarios under which one approach outperforms others are described.     

A comparison of some simple methods used to detect unstable temperature responses in tree-ring chronologies

Temporal stability of the relationship between a potential proxy climate record and the climate record itself is the foundation of palaeoproxy reconstructions of past climate variability. Dendroclimatologists have spent considerable effort exploring the issue of temporal instability of temperature records at high-latitude and −altitude Northern Hemisphere sites. Much of this work has focused on the Divergence Problem in which the modern ends of tree-ring chronologies exhibit pronounced departures from the climate-proxy relationships of preceding decades. However, there has been little scrutiny of how different methods might influence determinations of temporal instability at either the local scale or across broader spatial domains. Here we use four sets of Southern Hemisphere (SH) chronologies and three sets of synthetic data with known interventions to compare four methodologies that have been widely used to assess the temporal stability of relationships between tree-ring series and climate. Our analyses demonstrate that a determination of temporal instability may be partially dependent on method used to examine data, that some methods are more sensitive to standardisation choice than others, and that all methods are better at detecting high- rather than low-frequency instability. In all cases, the relatively modest strength of the relationships between the selected SH ring-width chronologies and temperature is likely to be an issue, especially if changes in trends are of interest. We recommend that robust assessment of temporal instability between tree-ring chronologies and observational climate data should use a range of methods and that unstable temporal relationships across space be carefully considered in the context of large climate field reconstructions.     

Evaluation of automated threshold selection methods for accurately sizing microscopic fluorescent cells by image analysis

The accurate measurement of bacterial and protistan cell biomass is necessary for understanding their population and trophic dynamics in nature. Direct measurement of fluorescently stained cells is often the method of choice. The tedium of making such measurements visually on the large numbers of cells required has prompted the use of automatic image analysis for this purpose. Accurate measurements by image analysis require an accurate, reliable method of segmenting the image, that is, distinguishing the brightly fluorescing cells from a dark background. This is commonly done by visually choosing a threshold intensity value which most closely coincides with the outline of the cells as perceived by the operator. Ideally, an automated method based on the cell image characteristics should be used. Since the optical nature of edges in images of light-emitting, microscopic fluorescent objects is different from that of images generated by transmitted or reflected light, it seemed that automatic segmentation of such images may require special considerations. We tested nine automated threshold selection methods using standard fluorescent microspheres ranging in size and fluorescence intensity and fluorochrome-stained samples of cells from cultures of cyanobacteria, flagellates, and ciliates. The methods included several variations based on the maximum intensity gradient of the sphere profile (first derivative), the minimum in the second derivative of the sphere profile, the minimum of the image histogram, and the midpoint intensity. Our results indicated that thresholds determined visually and by first-derivative methods tended to overestimate the threshold, causing an underestimation of microsphere size. The method based on the minimum of the second derivative of the profile yielded the most accurate area estimates for spheres of different sizes and brightnesses and for four of the five cell types tested. A simple model of the optical properties of fluorescing objects and the video acquisition system is described which explains how the second derivative best approximates the position of the edge.     

A quick and simple biostrip technique for detection of lactose

A quick, simple and economical biostrip technology was developed for estimation of lactose by immobilizing -galactosidase, galactose oxidase and horseradish peroxidase on to a polymeric support. The biostrip is dipped in milk or milk products and, from the colour that develops from an added chromogen, the concentration of lactose can be estimated from < 20 to 100+g l^–1. The biostrips may be used in dairy industries, hospitals and remote areas where expensive instruments are not available.     

Evaluation of automated threshold selection methods for accurately sizing microscopic fluorescent cells by image analysis.

The accurate measurement of bacterial and protistan cell biomass is necessary for understanding their population and trophic dynamics in nature. Direct measurement of fluorescently stained cells is often the method of choice. The tedium of making such measurements visually on the large numbers of cells required has prompted the use of automatic image analysis for this purpose. Accurate measurements by image analysis require an accurate, reliable method of segmenting the image, that is, distinguishing the brightly fluorescing cells from a dark background. This is commonly done by visually choosing a threshold intensity value which most closely coincides with the outline of the cells as perceived by the operator. Ideally, an automated method based on the cell image characteristics should be used. Since the optical nature of edges in images of light-emitting, microscopic fluorescent objects is different from that of images generated by transmitted or reflected light, it seemed that automatic segmentation of such images may require special considerations. We tested nine automated threshold selection methods using standard fluorescent microspheres ranging in size and fluorescence intensity and fluorochrome-stained samples of cells from cultures of cyanobacteria, flagellates, and ciliates. The methods included several variations based on the maximum intensity gradient of the sphere profile (first derivative), the minimum in the second derivative of the sphere profile, the minimum of the image histogram, and the midpoint intensity. Our results indicated that thresholds determined visually and by first-derivative methods tended to overestimate the threshold, causing an underestimation of microsphere size. The method based on the minimum of the second derivative of the profile yielded the most accurate area estimates for spheres of different sizes and brightnesses and for four of the five cell types tested. A simple model of the optical properties of fluorescing objects and the video acquisition system is described which explains how the second derivative best approximates the position of the edge.     

A comparison of methods for quantitative analysis of feeding selection of fishes

Synopsis Predator-prey data were obtained in a study of feeding ecology of land-locked alewife,Alosa pseudoharengus, in Claytor Lake, Virginia, and subjected to two indices of electivity as well as a nonparametric paired-comparisons statistical test. Values obtained from the two indices were often contradictory with each other and the statistical test. Attributes of the statistical procedure render it more appropriate than electivity indices to describe feeding selectivity in fish populations. Results of the study also demonstrated the importance of considering the size composition of zooplankton populations in prey preference studies; measures of selection were often positive for zooplankters 1.0 mm while negative for those of the same prey group < 1.0 mm length. Because numerous problems are inherent with in situ feeding selectivity studies of planktivorous fishes, selectivity determinations, regardless of methodology, should be construed in a relative rather than absolute context.     

A comparison of methods for morphological studies of cultured cells

Summary A number of fixation methods for different types of cells in culture were compared, and the best preservation of nuclear and cytoplasmic details was obtained by fixation with Bouin's solution for 15 min, prior to staining with hematoxylin and eosin. All of the fixatives, including Bouin's solution, damaged various structures, notably the peripheral glas-attached cytoplasm and the intercellular connections. Micrographs obtained by bright field, phase contrast, and interference contrast (Nomarski) microscopy are presented. Much more realistic pictures, bringing out details not observed after fixation and staining, were obtained by Nomarski microscopy of living, unfixed cultures. Most conspicuous were numerous thin, cytoplasmic, cilia-like extensions, concentrated on the glass-attached peripheral margins, which were also visible on other cell surfaces and as intercellular connections. These structures were most characteristic of SV40-transformed human amnion cells. Although fixation and staining emphasize certain cell components (for example, inclusion bodies), many aspects of cellular morphology are better demonstrated by observing living cells by interference microscopy or by Nomarski interference contrast microscopy. Surface features of unfixed cells, seen by Nomarski interference contrast microscopy, were similar to the surface features of glutaraldehyde-osmium tetroxide-fixed cells studied as metallic replicas in the electron microscope. Supported in part by National Cancer Institute Research Grant CA-08748 and contributions from the Albert Soiland Cancer Foundation.     

A further study on nucleolar silver stained granules in some mononuclear-lymphoid bone marrow cells

Nucleolar silver stained granules (SSGs) representing nucleolus organizer regions (NORs) were investigated in human as well as rabbit bone marrows after visualization with standardized silver reaction for non-histone nucleolar argyrophilic proteins. The results indicated that few mononuclear lymphoid blast-like cells in investigated bone marrows are characterized by large irregularly shaped nucleoli which contain a larger number of SSGs than myeloblasts or proerythroblasts as well as immature or stimulated lymphocytes. Since according to previous studies the number of nucleolar SSGs decreased in the course of the erythroid, granulocytic and lymphocytic differentiation and maturation, a possibility exists that the described mononuclear lymphoid blast-like cells are even less differentiated and immature than committed stem cells for mentioned cell lines.     

A comparison of some different methods for purifying core temperature data from humans

Nine healthy females were studied about the time of the spring equinox while living in student accommodations and aware of the passage of solar time. After 7 control days, during which a conventional lifestyle was lived under a 24h “constant routine,” the subjects lived 17 × 27h “days” (9h sleep in the dark and 18h wake using domestic lighting, if required). Throughout the experiment, recordings of wrist activity and rectal (core) temperature were taken. The raw temperature data were assessed for phase and amplitude by cosinor analysis and another method, “crossover times,” which does not assume that the data set is sinusoidal. Two different purification methods were used in attempts to remove the masking effects of sleep and activity from the core temperature record and so to measure more closely the endogenous component of this rhythm; these two methods were “purification by categories” and “purification by intercepts.” The former method assumes that the endogenous component is a sinusoid, and that the masking effects can be estimated by putting activity into a number of bands or categories. The latter method assumes that a temperature that would correspond to complete inactivity can be estimated from measured temperatures by linear regression of these on activity and extrapolation to a temperature at zero activity. Three indices were calculated to assess the extent to which exogenous effects had been removed from the temperature data by these purification methods. These indices were the daily variation of phase about its median value; the ratio of this variation to the daily deviation of phase about midactivity; and the relationship between amplitude and the square of the deviation of phase from midactivity. In all cases, the index would decrease in size as the contribution of the exogenous component to a data set fell. The purification by categories approach was successful in proportion to the number of activity categories that was used, and as few as four categories produced a data set with significantly less masking than raw data. The method purification by intercepts was less successful unless the raw data had been “corrected” to reflect the direct effects of sleep that were independent of activity (a method to achieve this being produced). Use of this purification method with the corrected data then gave results that showed least exogenous influences. Both this method and the purification by categories method with 16 categories of activity gave evidence that the exogenous component no longer made a significant contribution to the purified data set. The results were not significantly influenced by assessing amplitude and phase of the circadian rhythm from crossover times rather than cosinor analysis. The relative merits of the different methods, as well as of other published methods, are compared briefly; it is concluded that several purification methods, of differing degrees of sophistication and ease of application to raw data, are of value in field studies and other circumstances in which constant routines are not possible or are ethically undesirable. It is also concluded that such methods are often somewhat limited insofar as they are based on pragmatic or biological, rather than mathematical, considerations, and so it is desirable to attempt to develop models based equally on mathematics and biology. (Chronobiology International, 17(4), 539-566, 2000)