Step deviation method
The step deviation method is a fast way to find the mean of grouped data when class widths are equal.
Practice This ConceptMain explanation
Teacher explanation
This method is used when the class intervals have the same width. We choose an assumed mean, divide deviations by class width to get small coded values, and then use a simpler formula. It is especially helpful in long tables because the numbers become easier to manage.
Example
If class width is 10 and a deviation is 20, then the coded deviation is 2.
Simple analogy
Same width, smaller numbers, faster mean.
Common confusion
Students forget that this method works best when all class widths are equal, so they apply it blindly to unequal intervals.
Exam tip
Check the class width first. If all intervals are equal, step deviation can save time in the board exam.
Answer writing and exam use
1-mark use
Write the exact meaning of step deviation method in one clean line.
2-mark use
Define step deviation method and add one example or condition.
3-mark use
Explain step deviation method, show the method or example, and mention the common mistake.
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