In these articles, I note that the R2 (or adjusted R2) doesn't increase very much and expect that the increase in R2 (or adjusted R2) may not be significant. However, the authors do not provide the F-test of the significance of the increase. Therefore, I would like to calculate this by hand. Can anyone tell me what the formula for this is?

For example, one study has two models with adjR2=.125 and .168. These two models vary by only 1 variable (which is included in model 2 but not in model 1). The accompanying F-stats are 3.113 and 4.848, the number of coefficients are 6 and 7 respectively, the number of observations 140.

The aythors claim that this additional variable is very important (it is stat.sign), but I wonder whether the increase in adjR2 is high enough to even continue with the larger model. How would I calculate that based on the reported results table only? I don't have the actual data, so can only work with what is reported in the article.

If possible, I'd like to know how to do this both for R2 and for adjR2, given that some authors report R2 and others report adjR2.

Thanks, Peter