Of all the leading indicators, one deserves its own treatment because it is timely, global, free, and mechanically elegant: the Purchasing Managers' Index (PMI). In the US the classic version is the ISM Manufacturing PMI (from the Institute for Supply Management); India's is the S&P Global India Manufacturing PMI and Services PMI (formerly branded Nikkei/IHS Markit); virtually every country has one, which makes the PMI the closest thing to a single global cycle thermometer.
What it is. Each month, purchasing managers at a panel of firms are asked a handful of simple questions about their business versus the prior month: are new orders higher, the same, or lower? Is production higher, same, or lower? Employment? Supplier delivery times? Inventories? The genius is in what is asked. Purchasing managers are the people who commit to buying inputs ahead of production, so their answers are a read on the near future of output, weeks before that output shows up in industrial-production or GDP data. And the questions are qualitative (up/down/same), so managers can answer instantly and accurately, with no waiting for audited numbers.
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How is the PMI calculated?
The diffusion-index construction (the mechanical heart; memorize this). Each question's answers are turned into a diffusion index with one formula:
Diffusion index = (% responding "higher") + 0.5 × (% responding "same")
The "same" responses are split evenly (half counted as up, half as down), which is what makes 50 the pivot: if exactly as many firms report higher as report lower, the index sits at 50. Therefore:
- PMI > 50 → the sector is expanding (more firms improving than worsening).
- PMI < 50 → the sector is contracting.
- PMI = 50 → no change.
- And the distance from 50 signals the pace (55 is a strong expansion; 52 is a tepid one; 45 is a real contraction), while the change from last month signals momentum.
The ISM Manufacturing headline PMI is a weighted composite of five sub-indices, each an equally-weighted (20%) diffusion index:
ISM PMI = 0.20 × (New Orders + Production + Employment + Supplier Deliveries + Inventories)
Worked Example computations use this directly. Two subtleties an analyst must carry:
- New Orders is the leading sub-index. Within the PMI, the new-orders component leads the headline (orders precede production), and the new-orders-minus-inventories spread is a favourite forward signal: rising orders against falling inventories means firms will have to ramp production to rebuild stock, a bullish setup. The reverse (falling orders, rising inventories) means a production cut is coming.
- Supplier Deliveries reads backwards. Slower deliveries push the index up (a longer wait signals demand outrunning supply, a boom), which is why in a supply shock like 2021 the supplier-deliveries component pushed PMIs up for the "wrong" reason (bottlenecks, not booming demand). Read the sub-components, not just the headline.
Is 50 always the line between growth and contraction?
Why the 50 line is not the same everywhere. For a mature economy like the US, 50 roughly separates growth from contraction. But the ISM itself notes that, because of long-run productivity growth, a manufacturing PMI above roughly 42.5 sustained over time is consistent with expansion of the overall economy (manufacturing can shrink while the larger economy grows). And for a fast-growing economy like India, the PMI almost never falls below 50 except in genuine shocks (it plunged to a record ~27 in April 2020's lockdown, an off-the-charts reading), so an Indian PMI of 52 is not "barely growing" the way it would be in Germany. It must be read against India's own history and trend. This is the M2.05 discipline in macro clothing: no number without a benchmark, and the benchmark for a PMI is its own history and its distance-and-direction from 50, not a universal constant.
Why does the PMI lead the economy?
Why PMIs lead, in one line: they survey the people who order the inputs (so they see demand first), they are timely (released on the first business day of the month, before any hard data for that month exists), and their new-orders component is a direct read on production not yet run. That is why a market-moving month often turns on the PMI print days before the GDP or IIP data confirm it.