Analysis of the national consumer price index using temporary series

Abstract

In Brazil the first studies referring to price indexes are from 1936. One of the price indexes used is the National Consumer Price Index (INPC). In July 1994 the Real Plan came into being and since its creation the minimum wage has experienced several periods of real losses and gains in relation to its nominal value [1]. This work aims to adjust a model of Time Series to the INPC series in order to verify the existence of trends, seasonality and interventions. Compare a model with and without intervention. The INPC time series was collected monthly by the IBGE from January 1980 to September 2017. The model that fit the best was the one with intervention. Intervention number 76 (04/1986) coincided with the period of governmental intervention in the creation of the crossed plan which began in March 1986. Intervention number 175 (07/1994) also had a significant result, since it was the period that was introduced the real plan. The policy did not interfere with the INPC, the changes occurred in the series were caused only by the change in the currency.