lechner and wunsch using an unusually rich data set find that a wide range of control variables which are not often available for this type of study affect impact estimates she also warns that estimated positive impacts for shortterm training within firms may partly reflect the selection of participants by firms the turning category in the oecdec labour market programme database can include longerterm jobsearch training work experience with some training elements classroom training training within firms and preapprenticeship programmes and special support for young apprentices