The interquartile range can be more useful when the first and fourth quartiles contain very little data, in other words there are only a very few high or low data points.
It is a simple but crude measure of the spread of data.
Outliers
Quartiles.
Quartiles are values that divide a sample of data into four groups containing the same number of observations. You will find details in the related link.
There are 5 quartiles in any data set.
To find the inner quartiles (Q1 and Q3), first arrange your data in ascending order. Q1 is the median of the lower half of the data, and Q3 is the median of the upper half. The inner quartiles divide the data into four equal parts. The outer quartiles also known as the minimum and maximum values, are the smallest and largest values in the data set.
The interquartile range can be more useful when the first and fourth quartiles contain very little data, in other words there are only a very few high or low data points.
It is a simple but crude measure of the spread of data.
Probably the box and whiskers plot, but there are others.
Outliers
Quartiles.
quartiles
The quartile deviation(QD) is half the difference between the highest and lower quartile in a distribution.
Definately more than 4 pieces of data (intuitively, otherwise at least 2 of your quartiles will fall in exactly the same place as each other). But I think that's the only limit on how much data you need - there is no upper limit.
Quartiles are values that divide a sample of data into four groups containing the same number of observations. You will find details in the related link.
A Box and Whisker Plot