A fallacy of generalization is a fallacy in which someone makes a generalization about a large population or group based on a sampling of that group that is too small. This fallacy can also occur when the sample group is large but lacks diversity, which means it still does not properly represent the total population or group. There are, however, situations in which a small sample group can be appropriate. A fallacy of generalization can also refer to a fallacy of composition, which occurs when the actions or thoughts of an individual are expanded to a larger group.
Also called a fallacy of hasty generalization, a fallacy of generalization often occurs accidentally through insufficient polling of sample groups. News broadcasts, for example, often use polls to indicate the attitudes or feelings of the general public within a particular country or region. These polls may be factually accurate and properly represent how the overall population feels, but this requires that large and diverse segments of the population are polled. When results are posted from a sample group that is small or not diverse, then a fallacy of generalization can occur and the findings may not be accurate.
One of the best ways a person can avoid making a fallacy of generalization is to ensure that any sample group used to determine information about a large population is sufficiently expansive and diverse. This can be difficult to achieve, however, since large populations not only increase the necessary size of the sample group but can also impact the appropriate amount of diversity that should be represented. In formal logic, such samplings can often be chosen and supported through mathematical statistics, but this is not typically used in informal logic. Due to this, someone can often attack an argument that uses a sample group by asserting that a fallacy of generalization has occurred.
The term “fallacy of generalization” can also be used to refer to another type of fallacy, more often referred to as a fallacy of composition. In this fallacy, someone uses the actions or thoughts of a single person or object to establish the actions or thoughts common within a larger population or group. If someone is talked to rudely by a young person, he or she might commit this fallacy by assuming that all young people are rude. This same type of fallacy of generalization can occur when someone buys a product from a company that ends up breaking quickly, and then assumes that all products from that company must be faulty.