STUDY OF FIXED EFFECT AND RANDOM EFFECT GAMMA DEGRADATION MODELS
PURPOSE. Construction of the random effect gamma degradation model results in the enlarged dimension of the vector of estimated parameters. Therefore, it is necessary to understand whether the introduction of the random effect allows to obtain more accurate estimates of model parameters or not. The paper compares the fixed effect and random effect gamma degradation models in terms of the estimation accuracy of their parameters. METHODS. The estimation accuracy of the highest likelihood of degradation model parameters is studied through the calculation of the Euclidean norm of the relative error of the obtained estimates for the different values of random effect based on the Monte-Carlo method. RESULTS AND THEIR DISCUSSION. The estimation accuracy of parameters is higher for the random effect degradation model with the increase of the random effect value. However, if unit-to-unit variability coefficient does not exceed 0.1, it is recommended to use the fixed effect degradation model for the higher estimation accuracy of model parameters. MAIN CONCLUSIONS. It is shown that the use of the random effect gamma degradation model is not advisable in the case of small sample volumes and an insignificant random effect.