New Delhi (CNN Business) Arvind Subramanian was the top economic adviser to the Indian government. Now he says the country's growth may have been overstated.

change in the method used to calculate India's GDP led to "a significant overestimation of growth," Subramanian writes in a research paper published by Harvard's Center for International Development.

In the paper, Subramanian estimates that India's economy grew at an average of 4.5% a year between March 2011 and March 2017 — far weaker than the 7% average rate reported by the government over that period.

Subramanian tracked 17 different economic indicators that are "strongly correlated" with growth, including electricity consumption, industrial production and commercial vehicle sales.

He found those indicators diverged sharply from the government's growth numbers after 2011, the first year of data affected by the change in methodology.