| Circular variables, which indicate direction or cyclical | | | | saw in consulting compared the distance and direction |
| time, can be of great interest to biologists, | | | | flown by male moths in comparison to unmated and |
| geographers, and social scientists. The defining | | | | mated female moths under different weather |
| characteristic of circular variables is that the beginning | | | | conditions. Another compared the direction and |
| and end of their scales meet. For example, compass | | | | distance traveled by beetles under two different |
| direction is often defined with true North at 0 degrees, | | | | conditions of crowding. Other examples include |
| but it is also at 360 degrees, the other end of the | | | | measures of wind and water flow direction to |
| scale. A direction of 5 degrees is much closer to 355 | | | | understand the movement of pollutants and the timing |
| degrees than it is to 40 degrees. Likewise, times that | | | | of events within a cycle, such as the when the number |
| represent cycles, such as times of day (best | | | | of heart attacks peaks within a week or how body |
| expressed on a 24 hour clock), day in a reproductive | | | | temperature fluctuates over a day. Note that time can |
| cycle, or month of a year are also circular. January, | | | | be considered either circular or linear. Time is circular |
| month 1 is closer to December, month 12, than it is to | | | | when it measures part of a cycle, such as the timing |
| June, month 6. | | | | of a daily event. It is linear when it measures length of |
| Examples of circular variables are abundant in biology, | | | | time, such as the number of days since an event. |
| geography, and the social sciences. One experiment I | | | | |