10: The bottom line (finally)

Let’s add two more columns to our table that contain the calculated and critical values of t and also the degrees of freedom.

  n mean

standard deviation


(standard error in the mean (SEM) difference of means SEDM tcalc tcrit (df=7)
Fish-2-Whale 8   267g   44g 15.6g  94g 18.5g 5.1
Generic Brand 8   173g   28g 9.9g

Our tcalc showed that the difference between tanks was about 5 times more than the random differences within tanks. And our tcrit showed that anything over 2.4 times would be statistically significant. So… finally, we can say definitively that Fish-2-Whale had a statistically significant effect on fish growth. Time to party!

Once more with gusto: if your tcalc is bigger than your tcrit, your results are statistically significant.