Type I and type II errors

For those of you who wanted to know, Type I and type II errors are defined as:

Type I error
An error that occurs when a researcher rejects the null hypothesis when it is true and concludes that a statistically significant relationship/difference exists when it does not.

Type II error
An error that occurs when a researcher accepts the null hypothesis when it is false and concludes that no significant relationship/difference exists when it does.

Source: Glossary of research methods published by the University of Bath, UK. http://www.bath.ac.uk/e-learning/gold/glossary.html#N1984 Accessed 02-10-06