Data Revisions And Forecasting Accuracy: An Econometric Analysis Based On Preliminary And Revised National Accounting Estimates

This paper entails an investigation of the effects of data revisions on forecasting accuracy, through use of preliminary and revised national accounting data compiled by the United Nations. A small model was estimated for each of fourteen countries and ex post“forecasts” generated for each country and each year of the period 1957–1964, using first preliminary and then revised data. A prior analysis of the data revisions indicated a strong and widespread tendency for the preliminary estimates to understate both levels and year‐to‐year changes. This is consistent with the findings of other studies. Two sets of forecasts obtained from the reduced form of the model were considered in relation to “actual” levels and changes, obtained from the revised data, and also in relation to each other. A strong downward bias was observed in the forecasts of levels based on preliminary data, and a weaker one in the forecasts of changes. The forecast discrepancies for different variables were found to be significantly correlated. The results suggest that a tendency toward understatement in preliminary data may account in part for the general tendency toward understatement in forecasts noted in other studies.