You can't own half a car. Height on the other hand, in continuous because it can take on any value within a range or interval depending on the precision of the measuring device. Catagorical data are measured using either a nominal or ordinal scale. Interval and ratio scales of measurement are numerical but differ in one important feature. Interval scales are ordered and the differences between points on the scale have the same meaning anywhere on the scale.
Temperature measurements are good examples of interval scales.
If the scale has all the feature of an interval scale and there is a true zero point, then it is called a ratio scale. Note that temperature in Celcius and Fahrenheit have a zero point on the scale, but this zero point is said to be arbitrary. Calendar time is interval Kelvin Temp is ratio Auto make is nominal Student grades is ordinal Movie ratings are ordinal Ok, Back to how to choose a statistical test. Let's keep it simple for now. On the left side of the table below are the goals of the study.