In the Article How to Calculate Market Shares Estelle Métayer describes some of the techniques you could apply when dealing with market share calculations:

- Why is an appropriate calculation of market share so important?

- Defining your market share according to your objectives;

- Market share calculations and pitfalls to avoid;

- How to calculate a market share when there is no data available.

Estelle shows how misleading a market-share calculation can be, and how companies can easily manipulate them. In order to use them effectively, it is recommended to write down your own assumptions and make sure you compare "apples with apples." As a result, it is warned of market-research reports which often lack explanations of how the market calculation was done.