Creating Grouped Frequency Distribution:
A) At first we have to determine the biggest and smallest values.
B) Then we have to Calculate the Range = Maximum - Minimum
C) Choose the number of classes wished for. This is generally between 5 to 20.
D) Find out the class width by dividing the range by the number of classes and then rounding up. We have to keep in mind that we must round up, not off. Generally 4.2 would round to be 4, however in rounding up, it becomes 5. When the range divided by the number of classes gives an integer value (without any remainder), then you can either add up one to the number of classes or add up one to the class width. Sometimes you are locked to a certain number of classes as of instructions. The Bluman text fails to state the case when there is no remainder.
E) Choose an appropriate starting point less than or equivalent to the minimum value. "The class width times, the number of classes" values ware most capable to cover. We require covering one more value than the range. We can finely follow the rule: The beginning point plus the number of class’s times the class width should be bigger than the maximum value. Here the lower limit is the starting point of the first class. We can get the rest of lower limits by continuously adding the class width to this lower limit.
F) To getting the upper limit of first class, we can subtract one from the lower limit of second class. Then carry on adding the class width to this upper limit to determine the rest of the upper limits.
G) Find out the boundaries by subtracting 0.5 units from lower limits and adding up to 0.5 units from upper limits. The boundaries are as well half-way among the upper limit of one class and the lower limit of subsequent class. It is not essential to find the boundaries whether you are trying to achieve it.
H) Now tally the data.
I) Find out the frequencies.
J) Now determine the cumulative frequencies. Based on what you are trying to achieve, it might not be essential to determine the cumulative frequencies.
K) Whenever essential, find out the relative frequencies and or relative cumulative frequencies.
To find the frequencies, it is possible to have TI-82 calculator for you. Initially we will have to determine the class width and class boundaries.