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# How To Find Number Of Classes In Statistics?

Short Tutorial on How To Find Number Of Classes In Statistics?

## Finding Number Of Classes In Statistics

There is no rule for determining the size, or number of classes for a statistical data . It is left to the experimenter to find class intervals which will produce a meaningful and useful statistics. William Navidi, in his textbook "Probability and Statistics for Engineers and Scientists" states that the number of classes should be approximately equal to the square root of the sample size.

Here listed are some common principles to determine the number of classes for a statistical data.

→There should be between 5 and 20 classes.
→ The class width should be an odd number. This will guarantee that the class midpoints are integers instead of decimals.
→ The classes must be mutually exclusive. This means that no data value can fall into two different classes
→ The classes must be all inclusive or exhaustive. This means that all data values must be included.
→ The classes must be continuous. There are no gaps in a frequency distribution. Classes that have no values in them must be included (unless its the first or last class which are dropped).
→ The classes must be equal in width. The exception here is the first or last class. It is possible to have an "below ..." or "... and above" class. This is often used with ages.
This is a short tutorial that explains you on how to calculate number of classed in statistics.

Formula:
K=1+3.3logN
Where,
K = Number of Classes
N = Total Number of Data in the Sample.

Example:
Consider a Statistical Data with a sample size of 10. Find the number of classes.

Step 1:
Given,
Total Number of Data in the Sample = 10

Step 2:
Applying the values in the formula,
K = 1 + 3.3logN
K = 1 + 3.3log10
K =
4.3