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Valle D, Mintz J, Brack IV. Estimation and interpretation problems and solutions when using proportion covariates in linear regression models. Ecology 2024; 105:e4256. [PMID: 38361276 DOI: 10.1002/ecy.4256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 12/28/2023] [Accepted: 01/18/2024] [Indexed: 02/17/2024]
Abstract
Proportion variables, also known as compositional data, are very common in ecology. Unfortunately, few scientists are aware of how compositional data, when used as covariates, can adversely impact statistical analysis. We describe here how proportion covariates result in multicollinearity and parameter identifiability problems. Using simulated data on bird species richness as a function of land use, we show how these problems manifest when fitting a wide range of models in R, both in a frequentist and Bayesian framework. In particular, we show that similar models can often generate substantially different parameter estimates, leading to very different conclusions. Dropping a covariate or the intercept from the model can solve the multicollinearity and parameter identifiability problems. Unfortunately, these solutions do not fix the inherent challenges associated with interpreting parameter estimates. To this end, we propose focusing the interpretation on the difference of slope parameters to avoid the inherent unidentifiability of individual parameters. We also propose conditional plots with two x-axes and marginal plots as visualization techniques that can help users better interpret their modeling results. We illustrate these problems and proposed solutions using empirical data from the North American Breeding Bird Survey. The practical and straightforward approaches suggested in this article will help the fitting of linear models and interpretation of its results when some of the covariates are proportions.
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Affiliation(s)
- Denis Valle
- School of Forest, Fisheries, and Geomatics Sciences, University of Florida, Gainesville, Florida, USA
| | - Jeffrey Mintz
- School of Natural Resources and Environment, University of Florida, Gainesville, Florida, USA
| | - Ismael Verrastro Brack
- School of Forest, Fisheries, and Geomatics Sciences, University of Florida, Gainesville, Florida, USA
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de Pinho FA, Mendes MO, de Magalhães VLP, Tinôco AAC, Seoane JHL, Rêgo FD, Soares RP, Barrouin-Melo SM. Clinical evolution of equine leishmaniasis with self-limiting cutaneous disease caused by Leishmania infantum in northeastern Brazil: A case report. Vet Parasitol Reg Stud Reports 2023; 41:100881. [PMID: 37208087 DOI: 10.1016/j.vprsr.2023.100881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Revised: 04/10/2023] [Accepted: 04/19/2023] [Indexed: 05/21/2023]
Abstract
Leishmania infantum infections have long been described in humans and dogs worldwide, but characterization of equine cases remains scarce. We describe the clinical evolution of a natural L. infantum infection to contribute to the diagnostic knowledge and epidemiology of equine leishmaniasis (EL). An auction-acquired four-year-old Mangalarga Marchador mare from Pernambuco state, presented a few subcutaneous nodules on the head and neck upon arrival at the purchaser's stud at Bahia state, in November of 2019. They progressed to multiple ulcerated and non-ulcerated nodules and spread to both right limbs in seven weeks. Hematology revealed anemia, lymphocytosis, monocytosis, and elevated plasma fibrinogen. Histopathology of the biopsied nodules identified a granulomatous dermatitis with macrophages containing Leishmania amastigotes. PCR detected Leishmania in skin lesions, but not in blood or spleen aspirate samples; ITS1 PCR-RFLP and DNA sequencing confirmed L. infantum species. A topical antiseptic and insect-repellent therapy and a monthly follow-up were established. All lesions improved progressively, without specific anti-Leishmania treatment, and 14 months later there was a consistent resolution. This first description of EL by L. infantum in an endemic area is relevant to emphasize the need for epidemiological studies, and to enhance clinicians' awareness for differential diagnosis.
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Affiliation(s)
- Flaviane Alves de Pinho
- Laboratory of Veterinary Infectious Diseases, Teaching Hospital of Veterinary Medicine, Federal University of Bahia, Av. Milton Santos 500, CEP: 40170-110, Salvador, BA, Brazil; Department of Veterinary Anatomy, Pathology and Clinics, School of Veterinary Medicine and Zootechny, Federal University of Bahia, Av. Milton Santos 500, CEP: 40170-110, Salvador, BA, Brazil
| | - Mariana Oliveira Mendes
- Laboratory of Veterinary Infectious Diseases, Teaching Hospital of Veterinary Medicine, Federal University of Bahia, Av. Milton Santos 500, CEP: 40170-110, Salvador, BA, Brazil
| | - Vitor Luiz Pereira de Magalhães
- Laboratory of Veterinary Infectious Diseases, Teaching Hospital of Veterinary Medicine, Federal University of Bahia, Av. Milton Santos 500, CEP: 40170-110, Salvador, BA, Brazil
| | | | | | - Felipe Dutra Rêgo
- Instituto Rene Rachou, Fundação Oswaldo Cruz, Av. Augusto de Lima, 1715 - Barro Preto, Belo Horizonte, CEP: 30190-009, MG, Brazil
| | - Rodrigo Pedro Soares
- Instituto Rene Rachou, Fundação Oswaldo Cruz, Av. Augusto de Lima, 1715 - Barro Preto, Belo Horizonte, CEP: 30190-009, MG, Brazil.
| | - Stella Maria Barrouin-Melo
- Laboratory of Veterinary Infectious Diseases, Teaching Hospital of Veterinary Medicine, Federal University of Bahia, Av. Milton Santos 500, CEP: 40170-110, Salvador, BA, Brazil; Department of Veterinary Anatomy, Pathology and Clinics, School of Veterinary Medicine and Zootechny, Federal University of Bahia, Av. Milton Santos 500, CEP: 40170-110, Salvador, BA, Brazil.
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