Istanbul Chamber of Commerce Revises Inflation Data

The Istanbul Chamber of Commerce revised the April inflation from 3.21% to 4.4% following calibration on software and calculation methods in the Consumer Price Index. The chamber also adjusted the May data from 2.8% to 1.6%. It was stated that these updates did not create a significant change in the general inflation trend.

Since the beginning of this year, the Istanbul Chamber of Commerce has been making retrospective revisions in the Istanbul Consumer Price Index that it started to announce. As a result of the update, inflation for April was revised upwards, while the May data was revised downwards.

The Istanbul Chamber of Commerce noted that the impact of these adjustments remained limited and did not have a significant effect on the general inflation trend.

The index, which has been published since the beginning of this year, was stated to have a wider product basket and a larger number of goods and services groups compared to the previous series in the announcement. The statement mentioned the need for calibration and updating in terms of normalization and chaining methods/operations, based on the observation by the Academic Science Committee.

The chamber stated two reasons for the calibration and updates in the announcement. The reasons were explained as follows:

“Firstly, it was understood that some improvements needed to be made in the software part of the index concerning the indexing process of product items showing seasonal characteristics such as apricots, cherries, and peaches to the base year. Secondly, it was observed that the high and diverging inflation tendencies among the past values of the items composing the index caused some items to suppress other items to a certain extent in the index calculations, and this had some effects, albeit low.”

The increase in the number of products subject to seasonality in the renewed basket compared to the old consumption basket and the occurrence of high price transitions from month to month due to frost disasters in our country in the spring months played a significant role in the emergence of the need for calibration and updating regarding seasonality and normalization.”

April and May inflation figures revised

Following these studies, the April data was revised upwards, while the May data was revised downwards.

While the April data was increased from 3.21% to 4.4%, the May data for Istanbul Chamber of Commerce inflation was revised from 2.8% to 1.6%.

After these adjustments, the monthly average inflation rate for the period of January 2024 – May 2025 was updated from 3.49% to 3.47%, and the annual average inflation rate was updated from 58.55% to 60.11%.

The statement mentioned, “It was deemed appropriate to carry out these calibration and updating processes without delay and to share them with the public as part of the institutional responsibility.”