Hasty generalization is a fallacy in which one reaches a generalization based on insufficient evidence, making a rushed conclusion without considering all of the variables. This cognitive bias purports the following:
A is true for B. A is true for C. Therefore, A is true for D, E, F, etc.
A recent study by Chu et al. (2016) reported that “the language abilities of children who communicated solely via listening and spoken language were significantly better than children who used sign language.”
This is a classic case of hasty generalization.
In the study, Chu looked at two groups of children: one that utilized only spoken language after implantation, and one that used total communication after implantation. Spoken language (in this case, English) is a robust language system in and of itself. Total Communication (TC) is not. TC, which has come to mean simultaneous communication (SimCom), is the practice of signing and speaking at the exact same time. This is well known to have negative effects on language development, as it degrades the signal of both languages. TC/SimCom are not languages. They are a form of pidgin, or an amalgamation of two languages without its own grammar and structure.
What is the ACTUAL conclusion of this study? The language abilities of children who communicated solely via listening and spoken languages were significantly better than children who used a pidgin-like combination of spoken and signed modalities.
Of course they were.
That would be like saying that children who are monolingual English speakers perform better on English language tasks than children who speak Franglais. Therefore, French is the problem. No. Franglais is the problem. Mixing two languages into a non-language is the problem. Comparing real languages to pidgins is the problem.
American Sign Language (ASL) is a fully formed and robust language equal to English. TC and SimCom are NOT. If the study had instead looked at children who use spoken English alone and children who use ASL and English separately in their own forms, they would have found very different results.
How is this hasty generalization? The researchers assumed that because language abilities in English are decreased (A) in children who use total communication (B) and in children who use simultaneous communication (C) then it must be true for children who use American Sign Language (D). This is faulty logic and a perfect example of hasty generalization.
Beware of studies that use hasty generalization. Overgeneralizing negative results from a group of children using TC/SimCom to include a real language like ASL is very bad science. Read these studies carefully. If they are being reported by another source, be sure to find and read the actual article.