When do we use step-deviation method.Please explain the method.
When the data is given in the form of large numbers, then sometimes it is difficult and even lengthy to find the mean by using the assumed mean method. In such cases, we follow another method called step deviation method. Using this method, we can further reduce the calculation.
The example of this case is given in NCERT textbook on page 269.
In this method the step deviations are taken and therefore the end result is multiplied by the magnitude of the common factor or i. Thus, by this method
σ = √((∑fdX2)/N-((∑fdx)/N )2 ) × i