precise generalities

The book discusses how there are several values between "one" and "all" and those values are the precise generalities. For example,

65% of students who take tap from Ms. Katie think she is the best teacher they have ever had. Sarah took Ms. Katie's tap class last year. So Sarah thinks Ms. Katie is the best teacher she has ever had.

This is not valid because there is 35% not accounted for. According to the example in the book, with this type of example, we can say that the 35% is the possibility that the premises can be true but the conclusion false, which makes it not a strong argument. If the percentages are low or high on the scale, not in the middle, than the argument becomes stronger. For example, if the percent was less than 10 or greater than 85 than I am assuming that it would be a stronger argument because there is a lesser chance that the conclusion could be false.