请教HLM中fixed effect 和 random effect 的问题

.微に酸袅袅

Hi， Kenny：
# c7 k: b( i2 a  O( `0 k) p2 T2 f
4 q# i8 X6 i+ g2 Z' Uwhen we use HLM，there are some paper just report the fixed effect，while most time I use the random effect，so my question is when shall we use fixed or random effect and their difference？
% m% L* Q. t4 |6 `
& T9 Y  W; q$ s8 K* Manother question is about the ground mean and the group mean， when we test the level 2 model， should we use group mean？can you give some guidance？
$ B* H2 p  ~4 p& T" c
* @5 L! N1 j  ]* Z* uBest，
Kelly
+ N. L; r4 m+ K- F/ F+ m

Kenneth

Kelly，這是個給國內同學用的問題網站，麻煩用中文提問。謝謝。