# Comparison of forecasting methods for retail data

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http://urn.fi/URN:NBN:fi:hulib-202006172997
 Title: Comparison of forecasting methods for retail data Author: Länsman, Olá-Mihkku Other contributor: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta University of Helsinki, Faculty of Science Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten Publisher: Helsingin yliopisto Date: 2020 Language: eng URI: http://urn.fi/URN:NBN:fi:hulib-202006172997 http://hdl.handle.net/10138/316577 Thesis level: master's thesis Degree program: Tietojenkäsittelytieteen maisteriohjelma Master's Programme in Computer Science Magisterprogrammet i datavetenskap Specialisation: Algoritmit Algorithms Algoritmer Discipline: none Abstract: Demand forecasts are required for optimizing multiple challenges in the retail industry, and they can be used to reduce spoilage and excess inventory sizes. The classical forecasting methods provide point forecasts and do not quantify the uncertainty of the process. We evaluate multiple predictive posterior approximation methods with a Bayesian generalized linear model that captures weekly and yearly seasonality, changing trends and promotional effects. The model uses negative binomial as the sampling distribution because of the ability to scale the variance as a quadratic function of the mean. The forecasting methods provide highest posterior density intervals in different credible levels ranging from 50% to 95%. They are evaluated with proper scoring function and calculation of hit rates. We also measure the duration of the calculations as an important result due to the scalability requirements of the retail industry. The forecasting methods are Laplace approximation, Monte Carlo Markov Chain method, Automatic Differentiation Variational Inference, and maximum a posteriori inference. Our results show that the Markov Chain Monte Carlo method is too slow for practical use, while the rest of the approximation methods can be considered for practical use. We found out that Laplace approximation and Automatic Differentiation Variational Inference have results closer to the method with best analytical quarantees, the Markov Chain Monte Carlo method, suggesting that they were better approximations of the model. The model faced difficulties with highly promotional, slow selling, and intermittent data. Best fit was provided with high selling SKUs, for which the model provided intervals with hit rates that matched the levels of the credible intervals. Subject: retail probabilistic forecasting Bayesian inference posterior approximation
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