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PubMed2002

Comparison of pesticide root zone model 3.12: runoff predictions with field data.

As part of a process to improve confidence in the results of regulatory modeling, predictions of pesticide root zone model (PRZM) 3.12 were compared with measured data collected in nine different runoff field studies. This comparison shows that PRZM 3.12 provides a reasonable estimate of chemical runoff at the edge of a field. Simulations based on the best choices for input parameters (no conservatism built into input parameters) are generally within an order of magnitude of measured data, with better agreement observed both for larger events and for cumulative values over the study period. When the model input parameters are calibrated to improve the hydrology, the fit between predicted and observed data improves (results are usually within a factor of three). When conservatism is deliberately introduced into the input pesticide parameters, substantial overprediction of runoff losses occur. Recommendations for future work to improve regulatory models include implementation of more sophisticated evapotranspiration routines, allowing for seasonal variation of various model parameters (such as curve numbers, crop cover, and Manning's surface roughness coefficients), better procedures for estimating site-specific degradation rates in surface and subsoils, and improved sorption routines.

Calibration↗
PubMed1995

Diving at altitude: a review of decompression strategies.

Diving at altitude requires different tables from those at sea level due to the reduction in surface ambient pressure. Several algorithms extrapolating sea-level diving experimental data have been proposed to construct altitude diving tables. The rationale for these algorithms is reviewed together with the conservatism of the resulting tables and decompression computer outputs. All algorithms are based on the adaptation of critical tissue tensions to altitude. These are linear extrapolation (LEM), constant ratio translation (CRT), and constant ratio extrapolation (CRE) of maximum permissible tissue tensions (M values). Either new tables using the altitude-adapted M values were put forward or sea-level tables are to be used through an operation called correction. In this review it is shown that for a given set of M values, CRT and CRE give the same result for no-decompression-stop dives; they always yield more conservative results than LEM. When decompression stops are used, CRT is more conservative than CRE. When applied to different sets of M values, the conservatism becomes a function of bottom time, depth, and altitude. The analysis shows that the tables derived using CRT of U.S. Navy (USN) schedules and CRE Boni et al. tables give more conservative results than LEM Bühlmann tables for higher altitude, longer bottom time, and deeper dives. Aviation altitude exposure decompression sickness (DCS) data are also addressed to compare different model outputs. When applied to USN and Royal Navy tables, LEM yields an altitude DCS limit of 8,581 and 8,977 m, respectively. On the other hand, the altitude limit calculated using CRE applied to USN M values and LEM Bühlmann tables is found to be below 6,000 m.

Aerospace Medicine↗
PubMed1977

The 'new' medical student: another view.

In this paper the authors examine some evidence concerning admission of a "new" type of student to medical school. Such students have been described as more socially concerned and committed to reform of the health care system than students of the 1950s. The hypothesis was that the new type of student was a temporary phenomenon, influenced by transitory sociopolitical events which had little impact on the institutionalized processes of medical education. Data consisted of responses to selected attitude statements by successive entering classes of medical students in one school of medicine from 1970 to 1975. Data were collected a second time from graduating seniors in 1974 and 1975 (entering classes of 1970 and 1971). The same information was collected from physician preceptors in 1975. Results suggest partial support for the hypothesis of decreasing liberalism among entering freshman after 1973, increasing conservatism among graduating seniors, and a high level of conservatism among physicians. Some exceptions to these trends are noted.

Achievement↗
PubMed1993

Attitudes of males on contraception: a KAPE survey.

Acceptance of Family Planning services has been at a very slow pace in Africa. It was generally believed that the African male, due to his conservatism, was an obstacle to the acceptance of contraception by the African female. The study however showed that this was not true. The attitude of the African male towards contraception has changed drastically during the last thirty years, from ultra-conservatism during the 60s to very liberal in the 80s and 90s. Further it can be said that the African male is as well informed and has the same degree of Family Planning and child spacing acceptance-level as his counterpart in the developed world. However the African male does not accompany his partner for Family Planning Counselling. The study showed that most African men associate Family Planning with the use of condoms and not other methods such as the pill or the intrauterine devices.

Botswana↗
PubMedDate not supplied

[Detection and analysis of Tetrahymena pyriformis 26S ribosomal DNA domain sequences, differing in degree of evolutionary conservation].

Domains of different evolutionary conservatism were defined in the 26S rDNA sequence of T. pyriformis. The fragment of studied DNA (1212 bp) showing high evolutionary conservatism was cloned. It was shown this fragment of DNA may be used to a probe for blot-hybridization analysis of the structure of rDNA from various taxa, protists to mammals. Superconservative and hypervariable domains were defined. The first are good for the primers for PCR analysis of rDNA from various taxa, the second--for species specific primers.

Animals↗
PubMedDate not supplied

Breast disease: a primer on diagnosis and management.

Currently, mammography is the only method of detecting nonpalpable, early breast cancer. At this stage, 90% of the cancers are curable. Clearly, this fundamental tenet accentuates the importance of compliance and knowledge of guidelines. Although risks of mammography are minimal to nil, interpretation occasionally can be challenging, with equivocal results. New technologies are being evaluated and advances in measurement of cellular electrical potential differentials in breast tissue have produced exciting results, when compared with mammography and ultrasound. These screening efforts have increased the diagnosis of both invasive and noninvasive ductal and lobular carcinoma of the breast. For DCIS in particular, conservative, contemporary treatment options exist. These include lumpectomy with breast irradiation excluding axillary dissection. Selected patients may be treated with only lumpectomy. Although breast carcinoma is a major focus due to incidence, morbidity and mortality, the varieties of benign conditions cause many women genuine concern. Treatment options for fibrocystic change run a gamut, including cost-effective basic dietary changes, vitamin use, "health"/natural type treatments, analgesic, as well as hormonal manipulations and, on occasion, surgical intervention. Fortunately, with most patients, common sense and conservatism prevail. The presence of fibroadenomas diagnosed clinically, by ultrasound or mammography, in women aged 18-25 and beyond can create perplexing diagnostic dilemmas. Should the lesion be removed or observed? Differences of opinion exist and must be tempered by recent observations that women with complex fibroadenomas, sclerosing adenosis, epithelial calcification or papillary appocrine changes have a two- to threefold increased risk of breast cancer. The key to management in all these clinical situations is individualization. Conservatism is particularly acceptable in women under the age of 25 if a fibroadenoma is not increasing in size or not psychologically disturbing. Provoked or unprovoked nipple discharge is a clinical conundrum for patients. It is unsuspected and unwanted. While some whitish discharges result from stimulation or medication, others may have a more subtle etiology. Serous, serosanguineous, or bloody discharges mandate evaluation. Duct injection mammography and frequent excision of ductal systems are necessary. The clinician cannot forget other less common conditions, such as thrombophlebitis, fat necrosis, or infection. All clinical conditions of the breast provide a constellation of diagnostic and management problems. They are of real concern for every woman and must be resolved in an appropriate, prompt, and conscientious fashion.

Adolescent↗
PubMed1978

Absorption of subretinal fluid after nondrainage retinal detachment surgery.

A total of 134 cases of retinal detachment treated with a single successful nondrainage operation were studied to assess the rate of absorption of subretinal fluid in the postoperative period. It has been found that the relationship of the tear to the buckle at the end of the operation is an indicator of the rate of absorption of subretinal fluid that can be expected in the postoperative period. The age of the detachment or the age of the patient did not appear to be significant factors in influencing absorption. In 28 cases (21%), absorption of subretinal fluid took longer than one week. This delay in absorption shows that conservatism regarding early reoperation should be urged unless a definite cause of failure (such as a missed tear) can be found.

Absorption↗
PubMed1980

Head and neck surgery--1960 to 1980.

The years 1960 to 1980 represent a period of assessment and advancement in head and neck surgery. Basic operations were broadly applied and extended in their radicality. These techniques were standardized and more recently have been modified by conservatism and the strong introduction of preoperative and postoperative irradiation for advanced neoplasms and those persons at high risk. Chemotherapy is attempting to gain a role. The greatest innovation during this period was the discovery and use of a great variety of regional flaps to assist in the rehabilitation of these large and dangerous wounds.

Head and Neck Neoplasms↗
PubMed1981

Does Peutz-Jeghers syndrome predispose to gastrointestinal malignancy? A later look.

Several reports have recently suggested an association between the development of intestinal carcinoma and the presence of Peutz-Jeghers syndrome. During the 45-year period between 1935 and 1979, 48 patients with Peutz-Jeghers syndrome were seen at the Mayo Clinic, Rochester, Minn, and followed up for a median period of 33 years. Carcinoma of the small or large intestine did not develop in any patient, with possibly one exception. Survival of patients with Peutz-Jeghers syndrome also was found to be similar to that of the general population. Therefore, skepticism continues about the premalignant potential of this rare syndrome, especially in the small intestine, and surgical conservatism should be practiced in its management.

Adult↗
PubMed2002

Making reviewers visible: openness, accountability, and credit.

Anonymity for peer reviewers remains the overwhelming norm within biomedical journals. While acknowledging that open review is not without challenges, this article presents 4 key arguments in its favor: (1) ethical superiority, (2) lack of important adverse effects, (3) feasibility in practice, and (4) potential to balance greater accountability for reviewers with credit for the work they do. Barriers to more widespread use of open review include conservatism within the research community and the fact that openness makes editors publicly responsible for their choice of reviewers and their interpretation of reviewers' comments. Forces for change include the growing use of preprint servers combined with open commentary. I look forward to a time when open commentary and review replace the current, flawed system of closed prepublication peer review and its false reassurances about the reliability of what is published.

Biomedical Research↗
PubMed1997

Intrasexual competition and body weight dimorphism in anthropoid primates.

Body weight dimorphism in anthropoid primates has been thought to be a consequence of sexual selection resulting from male-male competition for access to mates. However, while monogamous anthropoids show low degrees of weight dimorphism, as predicted by the sexual selection hypothesis, polygynous anthropoids show high variation in weight dimorphism that is not associated with measures of mating system or sex ratio. This observation has led many to debate the role of other factors such as dietary constraints, predation pressure, substrate constraints, allometric effects, and phylogeny in the evolution of anthropoid weight dimorphism. Here, we re-evaluate variation in adult body weight dimorphism in anthropoids, testing the sexual selection hypothesis using categorical estimates of the degree of male-male intrasexual competition ("competition levels"). We also test the hypotheses that interspecific variation in body weight dimorphism is associated with female body weight and categorical estimates of diet, substrate use, and phylogeny. Weight dimorphism is strongly associated with competition levels, corroborating the sexual selection hypothesis. Weight dimorphism is positively correlated with increasing female body weight, but evidence suggests that the correlation reflects an interaction between overall size and behavior. Arboreal species are, on average, less dimorphic than terrestrial species, while more frugivorous species tend to be more dimorphic than folivorous or insectivorous species. Several alternative hypotheses can explain these latter results. Weight dimorphism is correlated with taxonomy, but so too are competition levels. We suggest that most taxonomic correlations of weight dimorphism represent "phylogenetic niche conservatism"; however, colobines show consistently low degrees of weight dimorphism for reasons that are not clear.

Animals↗
PubMed1996

Hopping and swimming in the leopard frog, Rana pipiens: II. A comparison of muscle activities.

Electromyography (EMG) was used to examine muscle activity of the major hip, knee, and ankle extensors during both hopping and swimming in leopard frogs. Chronic EMG electrodes were implanted for periods of 7-10 days. This permitted us to record EMG activities during both hopping and swimming from the same electrode, allowing a direct comparison of the timing and amplitudes of muscle activity between the two behaviors. We could then relate these activities to the kinematics of locomotion. In both behaviors, all three extensors were synchronously activated 30-50 ms before limb extension began. However, the hip extensor turned on relatively earlier in hopping than in swimming when on time was expressed as percent of stride. The hip and knee extensors were activated relatively longer in hopping and the ankle extensor relatively longer in swimming. The amplitudes of the rectified, integrated EMG signals were roughly twice as large in hopping as in swimming for all three muscles, supporting the notion that propulsion in hopping requires more force than in swimming. The EMG burst durations differed little between the muscles or, in relative duration, between the behaviors. As has been found in other quadrupeds, the EMG bursts began before visible movement and ceased at or before hindlimb extension was completed. In our animals, however, we found a consistent, low level (10-30% of maximum amplitude) of EMG activity that continued 60-200 ms past the end of the burst and into the suspension periods in both hopping and swimming. We hypothesize that this unusual activity may be present in frogs so that the hind limb remains aero(hydro)dynamically stable as the frog arches through its leap or glides in swimming following completed limb extension. Thus, the timing and pattern of the EMG bursts are consistent with those present in other tetrapods and support conservatism of neural control. However, the prolonged low-level activity suggests flexibility in the control pattern and variation according to specific behaviors.

Animals↗
PubMed2000

Power comparisons for tests of trend in dose-response studies.

The Cochran-Armitage test for trend is a popular statistical procedure for detecting increasing or decreasing probabilities of response when a categorical exposure is ordered. Such associations may arise in a variety of biomedical research settings, particularly in dose-response designs such as carcinogenicity experiments. Previously, computing limitations mandated the use of the asymptotic trend test, but with the availability of new algorithms, increased computing power, and appropriate software the exact trend test is now a practical option. Nevertheless, the exact test is sometimes criticized on the grounds that it is conservative. In this paper we investigate the implications of this conservatism by comparing the true type I error and power of three alternative tests of trend - the asymptotic test, the exact test and an admissible exact test proposed by Cohen and Sackrowitz. The computations are performed by an extension to the network algorithm of Mehta et al. This allows us to make precise power comparisons between the tests under any given design without resorting to simulation. We show how this tool can guide investigators in choosing the most appropriate test by considering the design of two-year carcinogenicity studies carried out by the National Toxicology Program. We additionally compare the tests for various other combinations of sample sizes and number of groups or levels of exposure. We conclude that the asymptotic test, while more powerful where it is valid, generally does not preserve the type I error. This violation of the a priori testing level can be greatly affected by imbalance in the data or unequal spacing of dose levels.

Algorithms↗
PubMed1999

On the homology of structures and Hox genes: the vertebral column.

Research on expression patterns of Hox genes has revealed a surprisingly high conservation among vertebrates. In agreement with this conservation, a correlation has been found between the anterior limits of expression areas of certain Hox genes and the borders between morphological regions of the vertebral axis. These similarities are striking and important, but also counterintuitive, unless there are strong selection pressures to protect this conservatism. It is important to identify the selective forces that maintain these conservative networks. These selective forces can be due to pleiotropy or to internal selection. Discussed are the selective factors that are involved in the evolutionary constraint on the number of cervical vertebral numbers in mammals. Factors involved are due to internal selection and involve susceptibility to cancer, stillbirths and neuronal problems. It is intriguing how similar genetic networks can lead to fundamentally different animals. Clearly the same genes are used for different purposes. It is therefore important to try to find these differences. The search, for homology between organisms, and the enthusiasm about similarities that come with it, at times impedes the discovery of such differences. I have searched the literature for differences within vertebrates in the functioning and expression patterns of Hox genes during the development of the vertebral axis. The ensuing implications for homology of structures and genes are discussed. The vertebral column is a promising model system for the evaluation of the relationship between homologous Hox genes and homologous structures because of the large conservation of Hox gene expression patterns along the anterior axis. However, extensive remodelling of the vertebrate column indicates that important changes in the genetic basis must have taken place. A survey of the literature indicates that the correlation between Hox gene expression areas and vertebral regions is not such that one can predict the borders between vertebral regions on the basis of Hox gene expression patterns. The involvement of Hox genes in the development of identity of vertebrae is complex and the problems regarding the value of gene expression patterns for the determination of anatomical homology are discussed.

Animals↗
PubMed2001

Articular area responses to mechanical loading: effects of exercise, age, and skeletal location.

How reliable are reconstructions of body mass and joint function based on articular surface areas? While the dynamic relationship between mechanical loading and cross-sectional geometry in long bones is well-established, the effect of loading on the subchondral articular surface area of epiphyses (hereafter, articular surface area, or ASA) has not been experimentally tested. The degree to which ASA can change in size and shape is important, because articular dimensions are frequently used to estimate body mass and positional behavior in fossil species. This study tests the hypothesis that mechanical loading influences ASA by comparing epiphyses of exercised and sedentary sheep from three age categories: juvenile, subadult, and adult (n = 44). ASA was measured on latex molds of subchondral articular surfaces of 10 epiphyses from each sheep. Areas were standardized by body mass, and compared to diaphyseal cross-sectional geometrical data. Nonparametric statistical comparisons of exercised and control individuals found no increases in ASA in response to mechanical loading in any age group. In contrast, significant differences in diaphyseal cross-sectional geometry were detected between exercised and control groups, but mostly in juveniles. The conservatism of ASA supports the hypothesis that ASA is ontogenetically constrained, and related to locomotor behavior at the species level and to body mass at the individual level, while variations in diaphyseal cross-sectional geometry are more appropriate proxies for individual variations in activity level.

Age Factors↗
PubMed1994

Electromyography of back muscles during quadrupedal and bipedal walking in primates.

Despite the extensive electromyographic research that has addressed limb muscle function during primate quadrupedalism, the role of the back muscles in this locomotor behavior has remained undocumented. We report here the results of an electromyographic (EMG) analysis of three intrinsic back muscles (multifidus, longissimus, and iliocostalis) in the baboon (Papio anubis), chimpanzee (Pan troglodytes), and orangutan (Pongo pygmaeus) during quadrupedal walking. The recruitment patterns of these three back muscles are compared to those reported for the same muscles during nonprimate quadrupedalism. In addition, the function of the back muscles during quadrupedalism and bipedalism in the two hominoids is compared. Results indicate that the back muscles restrict trunk movements during quadrupedalism by contracting with the touchdown of one or both feet, with more consistent activity associated with touchdown of the contralateral foot. Moreover, despite reported differences in their gait preferences and forelimb muscle EMG patterns, primates and nonprimate mammals recruit their back muscles in an essentially similar fashion during quadrupedal walking. These quadrupedal EMG patterns also resemble those reported for chimpanzees, gibbons and humans (but not orangutans) walking bipedally. The fundamental similarity in back muscle function across species and locomotor behaviors is consistent with other data pointing to conservatism in the evolution of the neural control of tetrapod limb movement, but does not preclude the suggestion (based on forelimb muscle EMG and spinal lesion studies) that some aspects of primate neural circuitry are unique.

Animals↗
PubMed2005

Statistical methods for the analysis of two-arm non-inferiority trials with binary outcomes.

The aim of this contribution is to give an overview of approaches to testing for non-inferiority of one out of two binomial distributions as compared to the other in settings involving independent samples (the paired samples case is not considered here but the major conclusions and recommendations can be shown to hold for both sampling schemes). In principle, there is an infinite number of different ways of defining (one-sided) equivalence in any multiparameter setting. In the binomial two-sample problem, the following three choices of a measure of dissimilarity between the underlying distributions are of major importance for real applications: the odds ratio (OR), the relative risk (RR), and the difference (DEL) of both binomial parameters. It is shown that for all three possibilities of formulating the hypotheses of a non-inferiority problem concerning two binomial proportions, reasonable testing procedures providing exact control over the type-I error risk are available. As a particularly useful and versatile way of handling mathematically nonnatural parametrizations like RR and DELTA, the approach through Bayesian posterior probabilities of hypotheses with respect to some non-informative reference prior has much to recommend it. In order to ensure that the corresponding testing procedure be valid in the classical, i.e. frequentist sense, it suffices to use straightforward computational techniques yielding suitably corrected nominal significance levels. In view of the availability of testing procedures with satisfactory properties for all parametrizations of main practical interest, the discussion of the pros and cons of these methods has to focus on the question of which of the underlying measures of dissimilarity should be preferred on grounds of logic and intuition. It is argued that the OR clearly merits to be given preference also with regard to this latter kind of criteria since the non-inferiority hypotheses defined in terms of the other parametric functions are bounded by lines which cross the boundaries of the parameter space. From this fact, we conclude that the exact Fisher type test for one-sided equivalence provides the most reasonable approach to the confirmatory analysis of non-inferiority trials involving two independent samples of binary data. The marked conservatism of the nonrandomized version of this test can largely be removed by using a suitably increased nominal significance level (depending, in addition to the target level, on the sample sizes and the equivalence margin), or by replacing it with a Bayesian test for non-inferiority with respect to the odds ratio.

Biopharmaceutics↗
PubMed2002

Hydration of biological molecules: lipids versus nucleic acids.

We used FTIR spectroscopy to comparatively study the hydration of films prepared from nucleic acids (DNA and double-stranded RNA) and lipids (phosphatidylcholines and phosphatidylethanolamines chosen as the most abundant ones) at room temperature by varying the ambient relative humidity in terms of solvent-induced structural changes. The nucleic acids and phospholipids both display examples of polymorphism on the one hand and structural conservatism on the other; even closely related representatives behave differently in this respect. DNA undergoes a hydration-driven A-B conformational transition, but RNA maintains an A-like structure independently of the water activity. Similarly, a main transition between the solid and liquid-crystalline phases can be induced lyotropically in certain phosphatidylcholines, while their phosphatidylethanolamine counterparts do not exhibit chain melting under the same conditions. A principal difference concerning the structural changes that occur in the studied biomolecules is given by the relevant water-substrate stoichiometries. These are rather high in DNA and often low in phospholipids, suggesting different mechanisms of action of the hydration water that appears to induce structural changes on global- and local-mode levels, respectively.

Animals↗