South Korea's manufacturing PMI showed renewed contraction in the sector in September after four consecutive months of expansion, with the survey's headline index falling sharply to a 13-month low of 48.3 from 51.9 in August. Respondents reported weaker current conditions and more subdued price pressures and also have less confidence about the outlook.

Survey respondents reported declines in output, new orders and new export orders in September. Respondents also reported a fall in payrolls after four consecutive increases and are less optimistic about the outlook for output growth over the next 12 months. The survey shows a smaller increase in input costs and the first fall in selling prices in more than a year.

The Purchasing Managers' Manufacturing Index (PMI) is based on monthly questionnaire surveys of selected companies which provide an advance indication of what is really happening in the private sector economy by tracking changes in variables such as output, new orders, stock levels, employment and prices across the manufacturing sectors.

Investors need to keep their fingers on the pulse of the economy because it dictates how various types of investments will perform. By tracking economic data such as the purchasing managers' manufacturing indexes, investors will know what the economic backdrop is for the various markets. The stock market likes to see healthy economic growth because that translates to higher corporate profits. The bond market prefers less rapid growth and is extremely sensitive to whether the economy is growing too quickly and causing potential inflationary pressures.

The Markit PMI manufacturing data give a detailed look at the manufacturing sector, how busy it is and where things are headed. Since the manufacturing sector is a major source of cyclical variability in the economy, this report has a big influence on the markets. And its sub-indexes provide a picture of orders, output, employment and prices.