scholarly journals Binary contrasts for unordered polytomous regressors

2020 ◽  
Author(s):  
Jeremy Freese ◽  
Sasha Johfre
Keyword(s):  
Observational Studies ◽  
The Other ◽  
Regression Coefficients ◽  
Reference Category

In observational studies, regression coefficients for categorical regressors are overwhelmingly presented in terms of contrasts with a reference category. For unordered regressors with many categories, however, this approach often focuses on contrasting different pairs of categories with one another with little substantive rationale for foregrounding those comparisons. Mean contrasts, which compare categories to the overall mean, provide an alternative to the reference category, but the magnitude of mean contrasts is conflated with the relative sizes of the categories. Instead, binary contrasts compare a category to all the other categories, allowing the familiar interpretation for dichotomous regressors. We provide a Stata package that computes binary contrasts.

scholarly journals Consistency of causal claims in observational studies: a review of papers published in a general medical journal

BMJ Open ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. e043339
Author(s):  
Camila Olarte Parra ◽  
Lorenzo Bertizzolo ◽  
Sara Schroter ◽  
Agnès Dechartres ◽  
Els Goetghebeur
Keyword(s):  
Medical Journal ◽  
Observational Studies ◽  
The Other ◽  
Research Papers ◽  
General Medical Journal ◽  
Outcome Relationship ◽  
Causal Statement ◽  
Data Source ◽  
Published Research ◽  
Causal Language

ObjectiveTo evaluate the consistency of causal statements in observational studies published in The BMJ.DesignReview of observational studies published in a general medical journal.Data sourceCohort and other longitudinal studies describing an exposure-outcome relationship published in The BMJ in 2018. We also had access to the submitted papers and reviewer reports.Main outcome measuresProportion of published research papers with ‘inconsistent’ use of causal language. Papers where language was consistently causal or non-causal were classified as ‘consistently causal’ or ‘consistently not causal’, respectively. For the ‘inconsistent’ papers, we then compared the published and submitted version.ResultsOf 151 published research papers, 60 described eligible studies. Of these 60, we classified the causal language used as ‘consistently causal’ (48%), ‘inconsistent’ (20%) and ‘consistently not causal’(32%). Eleven out of 12 (92%) of the ‘inconsistent’ papers were already inconsistent on submission. The inconsistencies found in both submitted and published versions were mainly due to mismatches between objectives and conclusions. One section might be carefully phrased in terms of association while the other presented causal language. When identifying only an association, some authors jumped to recommending acting on the findings as if motivated by the evidence presented.ConclusionFurther guidance is necessary for authors on what constitutes a causal statement and how to justify or discuss assumptions involved. Based on screening these papers, we provide a list of expressions beyond the obvious ‘cause’ word which may inspire a useful more comprehensive compendium on causal language.

Evaluation of the Impacts of Chemotherapeutics on Odontogenesis Process: Findings from a Systematic Review

2019 ◽  
Vol 36 (03) ◽  
pp. 210-218
Author(s):  
Camila Valente Smith ◽  
Grazyelle Sebrenski da Silva ◽  
Felipe Rodolfo Pereira da Silva ◽  
José Fernando Marques Barcellos ◽  
Silvânia da Conceição Furtado
Keyword(s):  
Systematic Review ◽  
Experimental Animal ◽  
Observational Studies ◽  
Animal Studies ◽  
Direct Analysis ◽  
The Other ◽  
Cochrane Library ◽  
Oncology Patient ◽  
Therapeutic Protocol ◽  
The Individual

AbstractThis study aimed to examine and recognize the impacts of antinoplastic chemotherapeutics on the development of dental germ, employing a systematic review. A retrieving in the literature was carried out, using several medical and scientifical databases (ClinicalKey, Cochrane Library, Google Scholar, MedLine, PubMed, and ScienceDirect), by two investigators separately. In the end of this systematic search, eight articles met the required criteria for inclusion and, therefore, composed the results. Among these, four articles are about observational studies in humans, and the other four about experimental animal studies. In both cases and species, anomalies such as microdontia, hypodontia/agenesia, and root shortening were observed. The severity and frequency varied according to the nature of the chemotherapeutics applied as well as the administered dosage and the patient's age at the time of first exposure. Through the results, it was possible to show the direct impacts of chemotherapy on the odontogenesis process as well as factors such as the type of chemotherapy, the age of the individual at the time of first exposure and the dosage used. All of those should be taken into account when choosing a therapeutic protocol for an oncology patient. Besides, we observed the need for more studies in this area and that these should be standardized in order to allow an objective and direct analysis of comparable parameters, even when different approaches are used.

3.4 Lactation Curves

1981 ◽  
Vol 5 ◽  
pp. 111-114
Author(s):  
P. D. P. Wood
Keyword(s):  
Common Sense ◽  
Study Strategies ◽  
The Other ◽  
Regression Coefficients ◽  
Decay Function ◽  
Environmental Constraint ◽  
Lactation Curve ◽  
Algebraic Description ◽  
Image Position ◽  
Two Parameters

An algebraic description of the lactation curve is a useful component of any model of the day-to-day production of lactating animals. Observation and common sense suggest that such a function should rise to a peak early in lactation and decline thereafter but simpler models have been used. Ostergaard (1979), for example, used a linear model to study strategies for concentrate feeding to obtain optimum feeding levels in high yielding dairy cows. His model waswhere y (t) was the yield in week t and a and b were the usual linear regression coefficients. The error term is omitted here and elsewhere for clarity. Gaines (1927) used the decay functionwhere A and k are the constants fitted to log y (t).These models, one linear, the other exponential, peak in Week 1 and require only two parameters. In this paper, more sophisticated functions are described and compared.A lactation curve is assumed to contain two components, one of which is the intrinsic biological drive to produce milk and the other is an environmental constraint upon it. The algebra may be justified by biological argument according to the skill and the leanings of the modeller.

The relationship between fall dormancy and germplasm source in North American alfalfa cultivars

1996 ◽  
Vol 76 (3) ◽  
pp. 429-433 ◽  
Author(s):  
D. T. Fairey ◽  
N. A. Fairey ◽  
L. P. Lefkovitch
Keyword(s):  
Genetic Diversity ◽  
Regression Analysis ◽  
Plant Height ◽  
North American ◽  
The Other ◽  
Regression Coefficients ◽  
Large Contribution ◽  
Partial Regression ◽  
Fall Dormancy ◽  
The Relationship

Most of the genetic diversity of North American alfalfa cultivars has been accounted for by nine germplasm sources listed in descending order of winter hardiness as follows: Medicago sativa ssp. falcata, Ladak, M. sativa ssp. xvaria, Turkistan, Flemish, Chilean, Peruvian, Indian and African. In most instances, the breeder assigns a fall dormancy score and the relative proportions of each of the nine germplasm source for each cultivar at registration. The fall dormancy score (1 = dormant to 9 = non-dormant), determined by measuring plant height in October after harvest in early September, is used to indicate cultivar adaptation for different regions. This study examines the relationship between germplasm composition and plant height, the equivalence of fall dormancy. The signs on the partial regression coefficients of a multiple regression analysis of plant height on the proportional content of the nine sources of germplasm showed that the fall dormancy fell essentially into two classes, namely, a dormant category, comprising cultivars containing a large contribution of Falcata and Ladak, and a non-dormant category, in which Indian and African germplasm predominate. This does not necessarily preclude the influence of any of the other germplasm sources on fall dormancy, since they represent a rich source of diversity. However, nine distinct classes were not recognisable, perhaps because of the lack of an exact equivalence between fall dormancy class and plant height of the fall regrowth. Since these observations have not been derived in a common nursery, the latitude and latitude × cultivar effects have been disregarded. These limitations should be recognized when using the currently assigned fall dormancy ratings to predict cultivar adaptation. Key words: Alfalfa, fall dormancy, sources of germplasm

Patterns of paediatric analgesic use in Africa: a systematic review

2012 ◽  
Vol 97 (12) ◽  
pp. 1086-1091 ◽  
Author(s):  
Parvaz Madadi ◽  
Ehijie F O Enato ◽  
Shir Fulga ◽  
Chinonye C Umeoduagu ◽  
Stuart M MacLeod ◽  
...  
Keyword(s):  
Observational Studies ◽  
African Country ◽  
Sickle Cell Anaemia ◽  
The Other ◽  
Essential Medicines ◽  
Drug Reactions ◽  
African Children ◽  
Who Standards ◽  
Analgesic Use ◽  
Suspected Adverse Drug Reactions

We conducted a systematic literature review with two objectives: (1) to assess reported patterns of analgesic use in African children and compare these observed patterns to the analgesics given in the WHO Essential Medicines List for Children (EMLc); and (2) to summarise outcomes related to effectiveness, adverse events, cost and accessibility of these analgesics. Eligible participants were children (≤12 years) living in any African country who received an analgesic administered with the intention of relieving pain in any setting. Thirty-four peer-reviewed, observational studies representing 7772 African children were accepted. Studies were conducted in 25 different regions of 12 countries. Pain was attributed to surgery, burns, sickle cell anaemia and conditions requiring palliation in 32% of children, and was unspecified in the other 68%. Of the three EMLc analgesics, paracetamol and ibuprofen were widely employed, constituting ∼60% of all analgesics, while morphine was used in 20 children (0.2%). There were 455 suspected adverse drug reactions which included 17 deaths. Analgesic use reported in African children appears to fall short of WHO standards.

Haul-out behaviour of two Ross seals off eastern Antarctica

2003 ◽  
Vol 15 (2) ◽  
pp. 257-258 ◽  
Author(s):  
COLIN SOUTHWELL
Keyword(s):  
Observational Data ◽  
Observational Studies ◽  
The Other ◽  
Accurate Assessment ◽  
Limited Information ◽  
Absolute Sense ◽  
Crabeater Seal ◽  
Abundance Estimates ◽  
Antarctic Seals ◽  
Using Data

Accurate assessment of the abundance of pinnipeds from visual surveys requires estimation of both the available (hauled-out) and unavailable (in-water) components of the population (Eberhardt et al. 1979). Continental estimates of the abundance of the four Antarctic seals are based on limited information on haul-out behaviour. In developing continental estimates, Erickson & Hanson (1990) corrected visual surveys of the hauled-out component of the species' populations using data from observational studies of haulout behaviour by Erickson et al. (1989). Erickson & Hanson (1990) point out that, because the observational studies did not account for an unknown fraction of seals that remained in the water during the peak haul-out period, their abundance estimates are minimum values. Further, Erickson & Hanson (1990) corrected the visual surveys for all four species using haul-out data for the crabeater seal only, as observational data for the other species were not available. This assumes that haul-out patterns are constant across species, which is largely untested. Consequently, there is potential for bias, in both a relative and absolute sense, in the estimated abundance of Antarctic seals.

scholarly journals 690 PB 262 EFFECT OF IRRIGATION ON THE YIELD AND YIELD COMPONENTS OF TOMATO

HortScience ◽  
1994 ◽  
Vol 29 (5) ◽  
pp. 531f-531
Author(s):  
Daniel Smeal ◽  
E.J. Gregory ◽  
R.N. Arnold ◽  
J. Tomko
Keyword(s):  
New Mexico ◽  
Line Source ◽  
Yield Components ◽  
Fruit Yield ◽  
The Other ◽  
Regression Coefficients ◽  
Average Weight ◽  
Positive Correlation ◽  
Yield And Yield Components ◽  
Marketable Fruit

A single sprinkler line-source was used to provide irrigation treatments to three tomato (Lycopersicon escu Mill.) varieties (`Baja', `Rowpac', and `Roza') during 1988 and 1989 in northwestern New Mexico. In both years, marketable fruit yield (Y) of all varieties increased linearly with increased irrigation (1). However, the regression coefficients describing the Y vs. I relationship differed with variety and year. In 1989, `Rowpac' Y ranged from 40.3 to 114.2 Mg ha-1 at levels of 31.5 and 62.5 cm, respectively. Yields of `Baja' and `Roza', while similar to those of `Rowpac' at low I levels, were 59% and 71% of `Rowpac' Y, respectively, at the highest level of irrigation. At any given I level, Y was lower in 1988 than in 1989. While average weight per fruit (wt/fruit) and number of fruit per plant (no/plant) increased with increasing I level in all varieties, increased Y in `Rowpac' had a higher positive correlation with no/plant (40 to 90) than with wt/fruit (85 to 120 g). Increasing Y in `Baja' on the other hand, correlated much better with increased wt/plant (100 to 195 g) than no/plant (20 to 45).

scholarly journals Stature Estimation from Hand and Foot Dimensions Reveals a Similar Allometric Relationship in Sudanese Arabs and Somalis

2020 ◽  
Author(s):  
F.V. Ramirez Rozzi ◽  
D. Gassimalla ◽  
N. Abdalazeem ◽  
F. Elamin
Keyword(s):  
Sexual Dimorphism ◽  
Anthropometric Measurements ◽  
The Other ◽  
Regression Coefficients ◽  
Body Parts ◽  
Allometric Relationship ◽  
Foot Length ◽  
Different Populations ◽  
Hand Length ◽  
The Relationship

Population-specific anthropometric standards serve as a guide to forensic practitioners for identification purposes. However, few studies have observed on whether the relationship between stature and body parts differs among populations. Our aim is to first assess the validity of using hand and foot dimensions to estimate stature in two geographically similar but linguistically different populations, Sudanese Arabs and Somalis, and then secondly to assess whether the relationship between hand and foot dimensions and stature differ among these populations. Standard anthropometric measurements were used to assess sexual dimorphism. Regressions were performed to establish the relationship between body parts and stature and were compared among the populations to describe the allometry. Comparisons between regression coefficients reveal that 1) stature has the same relationship with hand and foot lengths in each population and 2) the relationship between stature/ hand length and foot length is the same (isometric) in both populations. These results suggest a close affinity between the two groups. Hand and foot length can be used to estimate the stature of individuals but not to identify sex or differentiate one population from the other.

scholarly journals Aptitud combinatoria general y específica de líneas tropicales de maíz usando probadores.

2006 ◽  
Vol 11 (1) ◽  
pp. 103
Author(s):  
Mauro Sierra ◽  
Fidel Marquez ◽  
Roberto Valdivia ◽  
Octavio Cano ◽  
Flavio A. Rodríguez
Keyword(s):  
Combining Ability ◽  
Winter Season ◽  
General Combining Ability ◽  
The Other ◽  
Regression Coefficients ◽  
Tropical Maize ◽  
Genetic Base ◽  
Best Value ◽  
Heterotic Pattern ◽  
B Lines

Thus, during autumn - winter season in 1996/97, there were evaluated in Cotaxtla, Ver. top crosses of tropical maize lines derived of several sources of germplasm such as: a) Recycled lines from H-513XVS-536, b) lines derived from a compound of wide genetic base (CABG3), c) Elite lines from Cotaxtla maize program and d) CIMMYT lines . There were used as testers, the lines LT154, and LT155 which are parents of H-513 and CML247 and CML254 which cross is an heterotic pattern defined by CIMMYT for the tropic . There were found lines like F31 x F30-4-3, F41 x F40-1-2, CABG3’-12-2-1-2-1, LT-174 y CML55 that registered good specific combining ability with tester 2 (LT-155) ;and F4 x F3-5-2 and CML15,with tester 4 (CML 254). On the other hand F4 x F5-5-1, CABG3’-12-2-1- 2-1, LT-174, CML13 and CML 15 had the best general combining ability. In relation with testers, it was found for recycled lines, that testers LT154 and CML254 registered the highest values for regression coefficients; It indicates that these testers identify the best lines; In lines derived from CABG3, tester LT155 registered the best value; In Elite lines, testers 2(LT155) and 3(CML247) identified better lines and from CIMMYT lines the best tester was CML254.

scholarly journals When size matters: advantages of weighted effect coding in observational studies

2016 ◽  
Author(s):  
Rense Nieuwenhuis
Keyword(s):  
Generalized Linear Model ◽  
Observational Studies ◽  
Regression Models ◽  
The Body ◽  
Sample Mean ◽  
Dummy Variables ◽  
Reference Category ◽  
The Past ◽  
Weighted Effect ◽  
Dummy Coding

To include nominal and ordinal variables as predictors in regression models, their categories first have to be trans- formed into so-called ‘dummy variables’. There are many transformations available, and popular is ‘dummy coding’ in which the estimates represent deviations from a prese- lected ‘reference category’. A way to avoid choosing a reference category is effect coding, where the resulting estimates are deviations from a grand (unweighted) mean. An alternative for effect coding was given by Sweeney and Ulveling in 1972, which provides estimates representing deviations from the sample mean and is especially useful when the data are unbalanced (i.e., categories holding different numbers of observation). Despite its elegancy, this weighted effect coding has been cited only 35 times in the past 40 years, according to Google Scholar citations (more recent references include Hirschberg and Lye 2001 and Gober and Freeman 2005). Furthermore, it did not become a standard option in statistical packages such as SPSS and R. The aim of this paper is to revive weighted effect coding illustrated by recent research on the body mass index (BMI) and to provide easy-to-use syntax for SPSS, R, and Stata on http://www.ru.nl/sociology/mt/wec/ downloads. For didactical reasons we apply OLS regres- sion models, but it will be shown that weighted effect coding can be used in any generalized linear model.

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