1. Explanatory Notes
Purchasing Managers Index (PMI) is an index summarized and compiled through the results of the monthly survey of enterprises purchasing managers. It covers every links of the enterprises, including purchasing, production, logistics, and so on. It is one of the leading indices which was commonly adopted by international society to monitor the macroeconomic trends, and played an important role in forecasting and monitoring. The threshold of PMI is usually using 50 percent as the cut-off point for economic performance. If PMI above 50 percent, it reflects the manufacturing economy is expanding; if less than 50 percent, it reflects the manufacturing economy is in recession.
The survey involves 31 divisions of manufacturing sector in the “Industrial Classification for National Economic Activities” (GB/T4754-2011). The survey sample was expanded from 820 to 3000 since January 2013.
3. Survey Methods
PPS (Probability Proportional to Size) sampling method was adopted in manufacturing purchasing managers’ survey. Using the divisions of the manufacturing sector as the selecting strata, the sample size of each division is proportional to its proportion of the value-added of the division to the total value-added of the manufacturing sector. Within the stratum, the samples are selected according to the probabilities proportional to their principal business revenues of the enterprises.
The survey was organized and conducted by staff members of survey offices, monthly through Online Reporting System of NBS by sending survey questionnaires to the purchasing managers of the selected enterprises.
4. Calculation Methods
The questionnaire of manufacturing purchasing managers survey covers 12 questions related to production, new orders, export orders, existing orders, finished goods inventory, purchase, import, purchase prices, raw materials, inventory, employees, suppliers, delivery time, production and business activities expectation and etc.. Diffusion index was calculated for each question, i.e. percentage of positive answers in number of enterprises plus half of the percentage in the same answers.
PMI is a composite index, which was calculated according to five diffusion indices (group indices) and their weights. 5 group indices and their weights are determined in accordance with their leading impact on the economy. Specifically, new orders index weighted 30 percent; production index weighted 25 percent; employees index weighted 20 percent; supplier delivery time index weighted 15 percent; raw materials inventory index weighted 10 percent. Of which, the supplier delivery time index is a converse index, and contrary calculation is needed when combines it into PMI.
5. Seasonal adjustment
The purchasing managers’ survey is a monthly survey, the data of the survey fluctuates very much for the influences of seasonal factors. The released PMI composite index and sub-indices are seasonally adjusted data.