Good day R-listers, i'm running a panel data regression and after performing the haussman test the conclusion was that my model is a fixed effect one. The problem is located on my explanatory variables which display week variations, and as it is well known fixed effect model gives weak results in a such case. So should 'i use the random effect instead??? my second question is the following when i run my regression with just one variable X (restricted model) they results said that it's very significant but when i add the rest of the variables, the findings show that it' isn't significant at all, so what should i' trust the first or the second results and why a such difference exist? Any hint would be highly appreciated. Thanks a lot in advance