In judging some types of inductive arguments you will be looking at sample size as scientists do when they are examining results of experiments. Similar to the concept of soundness for deductive arguments, a strong inductive argument with true premises is termed cogent . To say an argument is cogent is to say it is good, believable, there is good evidence that the conclusion is true. The concept of true premises sometimes bothers people. We live in a relativistic world.
Truth is what is generally accepted to be true or accepted to be demonstrated.
Some premises are unproblematic for all but the diehard relativist philosopher. If I say my shirt is red, you can check my shirt to see whether I'm lying. Other statements are harder to verify. And, sometimes when new information becomes available, an argument that used to look sound doesn't look so good anymore. Because of cooperative nature of this enterprise it is surprisingly difficult to devise arguments that students will be comfortable labeling sound or cogent.