The fallacy of drawing a conclusion about an entire group of people or things based on an undersized sample of the group is known as:

The answer is "Hasty generalization".

Hasty generalization is a kind of logical fallacy. A fallacy is a contention that depends on mixed up thinking. When one makes a hurried speculation, he applies a conviction to a bigger populace than he should in view of the data that he has.  

For instance, if my sibling likes to eat a great deal of pizza and French fries, and he is sound, I can state that pizza and French fries are solid and don't generally make a man fat. Be that as it may, I don't have a sufficiently extensive example populace to make this case. I have summed up in light of one individual.