Raul, First, have you checked that you actually have values for all your variables for all 20 quarters? Could one of your dummy variables have missing values, for example? Second, are these data sampled at regular (quarterly) intervals? If so, shouldn't you have 40 observations between 1981:1 and 1990:4? HTH, PS From: gretl-users-bounces(a)lists.wfu.edu [mailto:gretl-users-bounces@lists.wfu.edu] On Behalf Of Raul Gimeno Sent: Tuesday, September 22, 2015 5:43 AM To: gretl-users(a)lists.wfu.edu Subject: [Gretl-users] Number of observations in OLS I have 20 quarter observations from 1981:1 to 1990:4 When I run an OLS-estimation with three dummy variables yt = ß0 + ß1*t + ß2 *D2 + ß3 *D3 + ß4 *D4 + ut I get a result with the titel « Model x : OLS, using observations 1986 :2-1990 :2 (T17). » It is not clear to me why Gretl takes 17 observations instead of 20 to run the OLS estimation. Thank you in advance Raul