Trend Break or Unit Root in GDP of Iran



It has been suggested that existing estimates of the long-run impact of a surprise move in income may have a substantial upward bias due to the presence of a trend break in 1970s (1350s) and 1980s (1360s) gross domestic product (contained oil) data of Iran. This article shows that the statistical evidence does not warrant abandoning the no-trend-break null hypothesis at the 5% significance level. A key part of the argument is that conventionally computed p values overstate the likelihood of the trend-break alternative hypothesis. This is because they do not take into account that, in practice, the data is chosen based on pretest examination of the data.