Definition of One Tailed Hypothesis

A one tailed hypothesis, also known as a directional hypothesis, is a type of statistical hypothesis that predicts the direction of the relationship or difference between variables being studied. It specifies whether the effect will be positive or negative in a particular direction.

Key Characteristics

• Directional: One tailed hypotheses make a specific directional prediction about the relationship or difference between variables.
• Exploratory: They are used when researchers have a clear expectation about the direction of the effect they are investigating.
• Testing One Direction: One tailed hypotheses allow researchers to focus the statistical analysis on one direction of the effect, potentially increasing statistical power.

Example

For example, suppose a researcher wants to investigate whether a new drug increases reaction time. A one tailed hypothesis would predict that the drug will decrease reaction time. This hypothesis implies that the drug has a specific direction of effect, and the researcher is only interested in statistically testing this direction.

Conversely, a two tailed hypothesis would predict that the drug will have an effect on reaction time without specifying whether it will increase or decrease it. In this case, the researcher is interested in statistically testing any difference in reaction time, regardless of the direction.