description

Sample Bias is created when a person does a study that omits evidence that contradicts one particular outcome, by accidental design, as opposed to by choice.

When the data is omitted deliberatly, that is known as selection bias.

examples

In the 1920s, a telephone survey was conducted to predict who would win the US election, and the Republican candidate had a huge majority. But he lost. It turns out that since phones were expensive, none of the poorer Democrat voters were ever asked.