Ignoratio Elenchi, also called irrelevant conclusion, is a fallacy that happens “when an argument purporting to establish a particular conclusion is instead directed to proving a different point.” (Copi and Cohen, 1990).
To put it simple the fallacy occurs when premises miss the mark.
A: “This study shows that traffic lights have a positive affect on driving safety. Therefore, traffic policing must be increased.”
This is clearly an irrelevant conclusion, since A’s premise (‘traffic lights support safety’) does not lead to her conclusion (‘traffic policing must be increased.’)
Many times this is called a non sequitur.
B: “I like pizza, you like pizza. Therefore, this television show is the best.”
This kind of thing often leaves people confused.
I. M. Copi and C. Cohen. Introduction to Logic. New York: MacMillan Publishing Company, 1990, p. 131-32.