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Financial basics: Manufacturing PMI
September 20, 2024
Open up the economic calendar and chances are you will see some mention of manufacturing PMI data. They typically attract the same attention as other publications such as GDP, employment figures, inflation numbers and the like. But what exactly is a manufacturing PMI?
PMI stands for Purchasing Managers’ Index. A PMI is a diffusion index, which is a tool used in economics to evaluate the general trend of a series of data points. It works by looking at the direction of each component in a group and then telling us what the overall direction of the group is.
For example, let’s take a group of ten businesses to evaluate their overall growth trend. Nine report a 10% reduction in activity; one reports a twofold increase. In this instance, calculating the average growth would give us a positive figure, which is true, but ignores the fact that most of those businesses are in decline. A diffusion index on the other hand would instantly let us know that the overall trend is firmly negative.
In the case of the manufacturing PMI, the figure is calculated according to the following formula:
PMI = [G × 1] + [NC × 0.5] + [D × 0]
Where:
G: Percentage reporting growthNC: Percentage reporting no changeD: Percentage reporting decline
How are the above data collected? It is actually as straightforward as asking people in key industrial positions what they observe, typically on a monthly basis. A PMI is essentially the result of survey data. A corporation or government body will contact senior executives working at hundreds of companies across all sectors of industrial activity and ask them for specific information about their company’s performance.
The information in question revolves around new orders, inventory levels, production output, supplier deliveries and finally employment within the company. Once everything has been collected, the overall PMI figure can be calculated based on the number of businesses reporting growth, contraction or simply no change at all. A PMI above 50 indicates a sector in expansion; a PMI below 50 indicates a sector in contraction.
You may be forgiven for thinking that the above methodology does not sound very scientific or objective. There will obviously be errors involved, inaccurate information, inherent biases on behalf of the reporting staff etc., not to mention the fact that the companies surveyed may not necessarily reflect broader industrial trends. On top of that, the exact way of collecting and processing the data may vary from country to country. These problems are by no means limited to PMI data by the way. For example, inflation and employment statistics face the same hurdles and often undergo significant corrections in the months following publication.
If anything, PMI figures are some of the more reliable on the economic calendar. It is a relative measure after all; the question really boils down to “is this month better or worse than the previous one”. Given that they provide new information relating to industrial trends, PMI data are considered leading indicators, offering insights into the economy before they manifest in the labour market or in GDP figures for example.
The credibility of PMI figures is further bolstered by the fact that huge entities such as S&P Global publish such data on an international scale, harmonising the process across many different areas of the world. Indeed, S&P Global covers 45 distinct economies, allowing for more consistent comparisons to be made between different countries.
Many countries will have several different bodies that calculate PMI data, such as the Institute for Supply Management in the US for instance, which publishes alongside the S&P Global but uses a slightly different methodology. In China, the National Bureau of Statistics and Caixin Indices both convey PMI data, with the former focusing on larger and state-owned enterprises and the latter being much broader in scale.
Of course, a PMI is not limited to the manufacturing sector. Similar calculations are made for other areas of the economy, such as the service or construction sectors. Services are in fact a much larger contributor to GDP than manufacturing, particularly in developed countries, so why the focus on manufacturing? Tradition is a large part of it; the manufacturing PMI dates back to the 1940s and predates the service index by half a century. It is also considered the more concrete of the two, given the more nebulous nature of the service sector. Fundamentally, most of us probably attribute more value to building airplanes than to ordering cappuccinos from each other, a stance which underlies much of the criticism of the aforementioned GDP figures. Whatever the reason, manufacturing PMIs remain a staple of the economic calendar and this is unlikely to change.
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