In the last few years, the tremendous growth in the use of clustered survey methods in data mining in the presence of cluster effects has dichotomised the subject of econometrics due to the nature and problems in the way the data is being gathered. This book develops and investigates diagnostic tests for such cluster effects. In addition, this book also considers several aspects of hypothesis testing problems associated with the testing for cluster effects using the multi-stage linear regression model. Throughout the book the principle of invariance is used to eliminate the nuisance parameters where possible, thus reducing the dimension of the testing problems