Balanced and unbalanced panels 口 Distinction o a notation to help with mechanics a The role of the assumption Mathematical and notational convenience 口 Balanced,NT Unbalanced: 2L T Is the fixed Ti assumption ever necessary? sUr modelsBalanced and Unbalanced Panels  Distinction  A notation to help with mechanics zi,t, i = 1,…,N; t = 1,…,Ti  The role of the assumption ◼ Mathematical and notational convenience:  Balanced, NT  Unbalanced: ◼ Is the fixed Ti assumption ever necessary? SUR models. N i i=1  T