what is a box plot?
It is "a graphic representation of a distribution by a rectangle, the ends of which mark the maximum and minimum values, and in which the median and first and third quartiles are marked by lines parallel to the ends." - dictionary.com
To Create A Box-And-Whisker Plot :
You start by ordering your data (putting the values in numerical order), if they aren't in order already.
1) You find the median of your data. The median divides the data into two halves. To divide the data into quarters, you then find the medians of these two halves.
If you have an even number of values - (the first median was the average of the two middle values, then you include the middle values in your sub-median data)
If you have an odd number of values - (the first median was an actual data point, then you do not include that value in your sub-median data) To find the sub-medians, you're only looking at the values that haven't yet been used.
You have three points: the first middle point (the median), and the middle points of the two halves "sub-medians". These three points divide the entire data set into "quartiles".
The top point of each quartile has a name, being a "Q" followed by the number of the quarter. So the top point of the first quarter of the data points is "Q1" (Q1 is also the middle number for the first half of the list, Q2 is also the middle number for the whole list, Q3 is the middle number for the second half of the list, and Q4 is the largest value in the list.)
Once you have these three points, Q1, Q2, and Q3, you have all you need in order to draw a simple box-and-whisker plot.
To Create A Box-And-Whisker Plot :
You start by ordering your data (putting the values in numerical order), if they aren't in order already.
1) You find the median of your data. The median divides the data into two halves. To divide the data into quarters, you then find the medians of these two halves.
If you have an even number of values - (the first median was the average of the two middle values, then you include the middle values in your sub-median data)
If you have an odd number of values - (the first median was an actual data point, then you do not include that value in your sub-median data) To find the sub-medians, you're only looking at the values that haven't yet been used.
You have three points: the first middle point (the median), and the middle points of the two halves "sub-medians". These three points divide the entire data set into "quartiles".
The top point of each quartile has a name, being a "Q" followed by the number of the quarter. So the top point of the first quarter of the data points is "Q1" (Q1 is also the middle number for the first half of the list, Q2 is also the middle number for the whole list, Q3 is the middle number for the second half of the list, and Q4 is the largest value in the list.)
Once you have these three points, Q1, Q2, and Q3, you have all you need in order to draw a simple box-and-whisker plot.