A quartile is the name of a mathmatical expression used in the calculation of statistics, and is often part of a five-part summary. Commonly composed, the five-part summary reflects so:

Minimum of n
Lower Quartile (Q1)
Median
Upper Quartile (Q3)
Maximum of n

The minimum value here is merely the lowest occuring variable of n.

The lower quartile can be found by using the equation: Q1=.25(n+1)

When calculating the lower or upper quartile, it is possible that your Number will be a solid integer. If this is the case, mere go to that number's place in the list and select it. Here is an example:

If the lower quartile is equal to three in the following set: 1, 5, 5, 6, 7, 7, you would choose the third number in the set, 5, as the lower quartile. If, however, it were 3.5, then you would take the third and fourth numbers, and find the difference. 6-5=1, and then multiply that difference by the decimal you got, in this case the ".5" in the 3.5. This number is .5, and then you would just add this number to the third number, 5. Therefor, your lower quartile would now be 3.5.

The median is simply the middle number in the set if you have an odd number of variables, or the average of the two in the center if you have an even number of variables, assuming of course that you have already put them in numerical order.

Finding the Upper quartile is the same as finding the lower quartile, replacing the .25 in the equation with .75

The maximum is simply the maximum value of n

Quar"tile (?), n. [F.quartile aspect, fr. L. quartus the fourth. See Quart.] Astrol.