Cognitive bias
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All fallacies and biasesCognitive biases list
Selection bias distorts a result because the people or cases you reached are not a fair stand-in for the group you want to talk about. The flaw is in who got into the sample, not only in how you do the arithmetic afterwards.
Selection bias is filed here as a bias. If you cannot point to that move in the remark in front of you, you do not yet have this bias. Disliking the conclusion is not enough, and a true premise does not repair a broken step.
This page adds no new definition and no statistic. The three scenes below only move the library’s example into a meeting, a news sentence, and a social feed. None of them is a reported case, and none of them carries a number.
The library’s example is the anchor, quoted so the later scenes cannot drift: “A survey about reading habits is posted only in a book-club forum, then used as a picture of “people in general.” Book-club members are already heavy readers.” The three that follow change the room and keep the step.
Picture that example in a meeting, aimed at someone who has to answer before the next item. If the room cannot give the reply on the card, it has not answered the point. It has used Selection bias. No survey of offices is claimed. The test is whether the step matches the card.
The same step can sit in a speech or a headline, where the pause is shorter and the audience is larger. Imagine the stored example said into a microphone and left unpacked. This is not a claim about a particular broadcast or a particular paper. The correction is still the reply on the card, not a different theory of the press.
Imagine the example as a caption. Agreement is not evidence the step was valid, and outrage is not evidence a different bias was in play. Match the step to the definition before you name it.
State the group the conclusion is about, then state who was actually asked and who could not have been. If those differ, narrow the conclusion or change the sample.
“That is Selection bias” is not yet an answer. Name the step, then ask the question the card tells you to ask. If the remark survives, drop the label. If it fails, you still owe a reason for what you think instead. The reply does not hand you a new conclusion.
Selection bias is easy to shout in place of a neighbour. The nearest card people mix this up with is Confirmation bias. Use the comparison linked under this section when you are unsure which name fits. The comparison quotes the cards. It does not invent a third definition.
Write down the sentence you think is the mistake. If it matches one definition, use that name. If it matches neither, do not force a label. If it matches both, answer the two steps separately.
A survey about overtime is sent only to people still in the office at 8pm, then described as the view of the whole company. What distorts it?
The options and the explanation open in the quiz. Scoring stays on this device. There is no pass mark on this card.
Selection bias distorts a result because the people or cases you reached are not a fair stand-in for the group you want to talk about. The flaw is in who got into the sample, not only in how you do the arithmetic afterwards.
A survey about reading habits is posted only in a book-club forum, then used as a picture of “people in general.” Book-club members are already heavy readers.
State the group the conclusion is about, then state who was actually asked and who could not have been. If those differ, narrow the conclusion or change the sample.