A survey of purchasing managers that leads the cycle — if you read the sub-indices.
intermediate · 4 min read · 15 XP
Manufacturing is a small and shrinking share of a modern developed economy, yet its purchasing managers’ survey is one of the most watched releases on the calendar. The reason is timing: manufacturing turns first, and the survey arrives before any hard data describing the same month.
A Purchasing Managers' Index is a diffusion index built from a monthly survey of the people who buy inputs for businesses. They are asked whether output, new orders, employment, delivery times and inventories are better, the same, or worse than last month.
The index is then constructed so that:
What a diffusion index cannot tell you
A PMI measures breadth, not magnitude. A reading of 55 means more firms improved than worsened. It does not say by how much. An economy where every firm grew 0.1% and one where a few firms grew enormously can print the same number.
Two consequences follow. First, PMIs are excellent at identifying turning points and poor at estimating growth rates. Second, the distance from 50 is a rough guide at best — do not convert it into a GDP forecast without a proper mapping.
Manufacturing is roughly a tenth of output in a modern service economy, but it is disproportionately cyclical. It involves durable goods, capital investment and inventories — all of which are postponable. When conditions deteriorate, firms defer a machine purchase long before households cut back on haircuts. Manufacturing therefore turns first, both down and up.
Add to that the timing. S&P Global publishes a flash estimate around the third week of the month it describes, based on the majority of responses, then a final reading at the start of the next. That flash is often the first quantitative read on the current month from any source — weeks ahead of hard data.
The headline is a weighted composite. The detail is where the information is.
| Sub-index | What it tells you |
|---|---|
| New orders | The single most forward-looking line — today's orders are next quarter's output |
| New orders minus inventories | A classic leading spread: orders rising while inventories fall means production must increase |
| Employment | An early read on the labour data still weeks away |
| Prices paid / input prices | Cost pressure in the pipeline — an inflation signal that predates CPI |
| Suppliers' delivery times | Lengthening usually means demand is outstripping supply, though it also spikes on disruption |
| Backlogs of work | Whether firms are working through a cushion or running out of one |
The delivery-times inversion
Lengthening delivery times normally signal strong demand and add to the headline index. During a supply shock they lengthen because supply chains are broken, which pushes the PMI up while the economy is getting worse. This inverted the signal materially during the pandemic. When you see delivery times driving a headline, check whether the cause is demand or disruption.
Direction and momentum over level. A rise from 46 to 49 is more useful than a flat 52. A survey's value is in the change.
The 50 line is a headline, not a cliff. Crossing 50 makes news, but a move from 51 to 50.5 is not economically different from 50.5 to 50. Do not let a round number create a trade.
Compare the same series across countries. S&P Global compiles PMIs on a harmonised methodology worldwide, which makes them genuinely comparable — unlike most national statistics. Relative PMI momentum between two countries is one of the cleaner fundamental inputs for a currency pair.
Sceptically. The headline crossed into expansion, but the improvement came from the wrong place. Falling new orders point to weaker output ahead, and lengthening delivery times may reflect supply problems rather than demand strength. This is a headline that will likely be reversed in coming months, and a currency rally on it is worth fading rather than chasing — provided the rest of your evidence agrees.
On flash PMI day, several countries report within a few hours of each other — usually Australia and Japan, then France, Germany and the eurozone, then the UK, then the US. That sequence makes it one of the best days on the calendar for trading relative momentum, since you get comparable surveys for both legs of a pair on the same morning.
What to remember
Manufacturing PMI is a diffusion index of purchasing managers where 50 divides expansion from contraction. It leads the cycle because manufacturing spending is the most postponable, and its flash estimate arrives weeks before any hard data for the same month — but it measures breadth rather than magnitude, so the sub-indices, especially new orders and prices paid, carry more information than the headline.