Abstract
The data modeling from longitudinal studies stands out in the current scientific scenario, especially in the areas of health and biological sciences, which induces a correlation between measurements for the same observed unit. Thus, the modeling of the intra-individual dependency is required through the choice of a covariance structure that is able to receive and accommodate the sample variability. However, the lack of methodology for correlated data analysis may result in an increased occurrence of type I or type II errors and underestimate/overestimate the standard errors of the model estimates. In the present study, a Gaussian mixed model was adopted for the variable response latency of an experiment investigating the memory deficits in animals subjected to cerebral ischemia when treated with fish oil (FO). The model parameters estimation was based on maximum likelihood methods. Based on the restricted likelihood ratio test and information criteria, the autoregressive covariance matrix was adopted for errors. The diagnostic analyses for the model were satisfactory, since basic assumptions and results obtained corroborate with biological evidence; that is, the effectiveness of the FO treatment to alleviate the cognitive effects caused by cerebral ischemia was found.
Highlights
In the past few years, there have been an increasing number of experiments in the areas of health and biological sciences, where the response variables are analyzed over time for the same experimental unit in order to check, for example, the performance of alternative treatments that could come to be used in healing patients with some kind of disease
Liu et al (2007) used a mixed model regression to quantitate the longitudinal effect of minocycline on the recovery of learning and memory function measured in the water maze task after inducing focal cerebral ischemia in rats, an effect that was associated with increased neurogenesis and reduced activation of microglia
It is observed that as the memory tests (MT) are applied, the animals of the fish oil (FO) group, regardless of the time window of treatment, take less time to find the actual hiding place as compared with the Veh (4, 8 and 12 hours) groups. This memory-protective effect of FO was apparently robust in the 4 hours TW group, given that latency was reduced to the level of the sham group throughout the various test days
Summary
In the past few years, there have been an increasing number of experiments in the areas of health and biological sciences, where the response variables are analyzed over time for the same experimental unit in order to check, for example, the performance of alternative treatments that could come to be used in healing patients with some kind of disease Pharmacological studies with these characteristics were done by Ferreira et al (2014) and Bacarin et al (2015) wherein the authors longitudinally evaluated (memory tests) the. Technology cognitive performance of animal groups submitted to cerebral ischemia and control groups with treatments of different durations, in the same way as when treated with different medications Studies with such characteristics belong to the category of repeated measurements, in which one or more response variables are assessed repeatedly in the same unit. The measurements are performed under different evaluation conditions and they are arranged over time, respecting an analysis
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