Recall that the Staiger-Stock rule of thumb stipulates that the F-statistic for the first-stage regression should exceed 10 in order for bIV to be useful. We’re getting a little bit ahead of ourselves, but sneak a look at equation (12.30) to see the relationship between the F-statistic for the regression of equation€(4.4)

and the t-statistic for b in that regression. According to this relationship, the value imposed by the Staiger-Stock rule of thumb as the threshold value for the F-statistic establishes an implicit threshold value for the t-statistic. What is this value? Why?