Although the level of control over demand may be problematic at times, it is more difficult to exert much control over the supply of employees. The external environment has a major influence here, and anticipating changes can be valuable. What practitioners can do is to increase their knowledge and understanding of their labour markets. Most organisations operate in a variety of labour markets and you should identify and research the ones that are relevant to you. These can be defined using the following factors, which must be considered in conjunction with each other.