Avaliação da imobilidade tônica em codornas de corte via análise de sobrevivência' / Tonic immobility evaluation in meat quail via survival analysis

Tonic immobility (TI) is a way to measure fear, as characterized by the reduced capacity to respond to external stimuli. The time spent in TI indicates the level of fear. Since TI is measured as the time until event occurrence, survival analysis stands out as a suitable statistical method to treat these data. We aimed to investigate the influence of possible factors (lines, sex and age) on fear behavior in meat quail (Coturnix coturnix) measured through TI by using survival analysis (non parametric Kaplan-Meyer method via logrank test). The dataset was composed by TI information provided by 50 animals from each line (UFV1 and UFV2) in each age (14 and 28 days of age), totalizing 200 records. Despite the slight difference between the two evaluated ages, there was no significance for this factor between each studied line, UFV1 (P= 0.1493) and UFV2 (P= 0.2583). The logrank test indicated significant difference (P= 0.0407) between levels of line/sex groups at 14 days of age. We noted that males from UFV2 line presented higher fear behavior in relation to males from UFV1 line. No significant differences were observed for this factor when considering 28 days of age.(AU)

An alternative method for assessing the equivalence among treatments in survival analysis / Um método alternativo para avaliar a equivalência entre tratamentos em análise de sobrevivência

This work aims to evaluate the use of parametric models instead of a nonparametric procedure to adjust survival curves related to different treatments, and to verify the equivalence among treatments by the multivariate method of cluster analysis. The dataset used to validate the method was obtained from a laboratory experiment with cutting ants. Eight colonies of cutting ants were used, each one receiving different treatments. The exponential, Weibull, log-normal, and logistic models were adjusted for each treatment, along with the usual Kaplan-Meier adjustment. The logistic model used was the best option for evaluating the survival of the ants. Therefore, this model was adjusted for each treatment. The estimates of the parameters of each adjusted model were clustered using Ward's method of multivariate technique of cluster analysis. Finally, heuristic techniques for choosing the number of clusters were applied in order to define the sets of equivalent treatments. For the dataset used, the proposed method was less laborious and as efficient as the logrank for the comparison of many survival curves.

Este trabalho tem como objetivo avaliar o uso de modelos paramétricos, ao invés do usual procedimento não paramétrico, no ajuste de curvas de sobrevivência em relação a diferentes tratamentos e ainda verificar a equivalência entre esses tratamentos através da técnica multivariada de análise de agrupamento. O conjunto de dados usado para validar o método foi obtido através de um experimento de laboratório com formigas cortadeiras. Oito colônias de formigas cortadeiras foram usadas, cada uma recebendo um tratamento diferente. Os modelos exponencial, Weibull, log-normal e logístico foram ajustados para cada tratamento além do usual ajustamento de Kaplan-Meier. O modelo logístico foi o mais aceitável para avaliar a sobrevivência das formigas. Portanto, esse modelo foi ajustado para cada tratamento. As estimativas dos parâmetros de cada modelo ajustado foram agrupadas utilizando o método de Ward da técnica multivariada de análise de agrupamento. Para o conjunto de dados usado, o método proposto foi menos trabalhoso e tão eficiente quanto o teste logrank para a comparação das várias curvas de sobrevivência.