One of the more disappointing economic reports last week was that the Institute for Supply Management’s proprietary PMI for manufacturing remained below 50 in August for the third consecutive month. The PMI is a composite measure of several dimensions of the supply chain, and any value below 50 reflects a contraction in U.S. manufacturing activity.
In contrast, the Manufacturing component of the Federal Reserve’s Industrial Production (IP) Index increased moderately during both June and July (the August values will be released this week on September 14th). The divergence of these two indices presents a conundrum: how can manufacturing be simultaneously increasing and decreasing?
The discrepancy primarily results from differences in the method by which each of these indices is constructed. The Federal Reserve determines monthly IP Manufacturing strictly by examining (actual and imputed) industrial output, sourced from various trade associations and censuses.
By comparison, the PMI is formed from surveys of ISM member businesses and reflects five components: new orders, production, employment, supplier deliveries, and inventories. Because it includes several components besides production, the PMI may contract even if current manufacturing volumes are increasing.
So, which of these two indices is superior? Or, more specifically, which index better contextualizes the environment for trucking? Although some analysts argue the PMI has inferior predictive power (e.g. Bachman, 2010), this relates more to its usefulness for forecasting economic recessions than its quality in measuring the current business climate.
Overall, both measures are valuable for carriers to use in evaluating their future outlook. The Industrial Production Index is informative about future volumes, especially over a longer term—goods that are produced are eventually going to be shipped, generating demand for trucks. The PMI speaks to the current manufacturing climate, and declines in the non-output portions of the PMI could foreshadow production declines to come.
Jeremy West, Internet Truckstop Economist