how many degrees of freedom does the​ t-statistic have
t-statistic If     β ^    {\displaystyle \scriptstyle {\hat {\beta }}}  is an ordinary least squares estimator in the classical linear regression model (that is, with normally distributed and homoscedastic error terms), and if the true value of parameter β is equal to β0, then the sampling distribution of the t-statistic is the Student's t-distribution with (n − k) degrees of freedom, where n is the number of observations, and k is the number of regressors (including the intercept).