Essentially, the trading concept of Quantitative Analysis involves the process of applying a business or financial technique that seeks to understand behavior within the currency market by applying a complex system of mathematical and statistical modeling, along with measuring of market values and research.
Generally this is made possible through the method of applying a series of numerical values to certain variables, with which quantitative analysts try to replicate reality mathematically and so predict changes and moves with the markets.
There are many reasons for employing a quant (as quantitative analysts are often affectionately known) as quantitative analysis itself can be carried out for a number of reasons, such as a performance evaluation, measurement, or valuation of a certain financial instrument. For example in foreign exchange terms for a certain trading pattern or style, while it can also be used to quite accurately to predict certain real world events such as changes in the price of shares and turning points in inflation.
In broader terms, however, quantitative analysis is more simply a way of measuring and interpreting certain things and events and can be used for more common paced tasks as calculating simple financial ratios such as earnings gained per share, or for more complicated reasons such as to calculate option pricing or discounted cash flow.
While there is no doubt that although quantitative analysis is indeed a powerful tool for evaluating investment potential, it's really only one side of the story and its counterpart, qualitative analysis must also be utilized in order to gain the full picture.