Survivorship bias or survival bias is the logical error of concentrating on the people or things that made it past some selection process and overlooking those that did not, typically because of their lack of visibility. This can lead to some false conclusions in several different ways. It is a form of selection bias.

Survivorship bias can lead to overly optimistic beliefs because failures are ignored, such as when companies that no longer exist are excluded from analyses of financial performance. It can also lead to the false belief that the successes in a group have some special property, rather than just coincidence (correlation "proves" causality). For example, if three of the five students with the best college grades went to the same high school, that can lead one to believe that the high school must offer an excellent education when, in fact, it may be just a much larger school instead. This can be better understood by looking at the grades of all the other students from that high school, not just the ones who made the top-five selection process.

Another example of a distinct mode of survivorship bias would be thinking that an incident was not as dangerous as it was because everyone communicated with afterwards survived. Even if one knew that some people are dead, they would not have their voice to add to the conversation, leading to bias in the conversation.

Nostalgia is grounded in survivorship bias. Things weren't better back then, despite what you might think. Just the bad things from bad then didn't stick around.