We have to carry out an empirical panel analysis of economic growth and see differences in factors of growth between groups of heterogeneous countries. As in economic growth much of the attention focuses on the form of the growth model estimated (factors included and the possibility of omitted factors) and this has to be a keystone of our paper, we would like to justify our election very well. To do so we need to use a strong, published and accepted model as baseline-model. What model (paper) would you recommend? Thank you very much.