In situations where one component of a package can be substituted for an adequate alternative then the price elasticity for that component can be much higher than suggested by the price elasticity of the overall package. For example, changes in an air travel price could result in the passenger changing to a different airline, route or another transport mode while still undertaking a similar journey. Therefore, the elasticity for the overall journey cannot be inferred from the air travel price elasticity and must instead be estimated on a separate basis.