Item cloning techniques can greatly reduce the cost of item writing and enhance the flexibility of item presentation. An important consequence of cloning is that it may cause variability in the item parameters. Recently, Glas and van der Linden (in press, 2005) proposed a multilevel item response model where it is assumed that the item parameters of a 3-parameter logistic (3PL) model or a 3-par...

Online virtual worlds such as Second Life provide a rich medium for unstructured human interaction in a shared simulated 3D environment. However, many human interactions take place in a structured social context where participants play particular roles and are subject to expectations governing their behaviour, and current virtual worlds do not provide any support for this type of interaction. T...