Houston offers a one year minimum . <| sep |> I always tell people how I would have loved Harry Potter to be a TV series ! <| sep |> From an econometric point of view you can never get a completely unbiased in the technical , econometric sense , NOT in the researcher is biased sort of way result . If you don ' t try to implement some control variables you will get an omitted variable bias which will likely overestimate the level of the wage gap . If you do include the more important control variables however you can get selection bias due due to the explanatory variables being themselves outcome variables , which can underestimate the wage gap . An example of this is education , which if you don ' t control for you will overestmiate the gender wage gap , but if youinclude you get some of the reverse causality effect that of their is a gender wage gap you would expect women to invest less in education . If you just regress earnings on a whole bunch of control variables and a gender dummy variable , you will likely underestimate the real wage gap .