# Statistical Method

### (C) Calculation of arithmetic mean in Frequency distribution:

There are two methods of calculation: (i) Direct method and (ii) Indirect method

(i) Direct method:

Step:

• Take mid value of each group as the value of

• Multiply x with to obtain

• Take sum of to obtain

• Divide by to get

• Use the formula

(ii) Indirect method:

There are two versions of indirect method.

(a) Based on assumed mean

Steps:

• Take mid value (x) of each group.

• Take some value of x as assumed mean (A)

• Deduct A from x to get

• Multiply by f to get

• Take sum of all value of to obtain

• Divide by to get

• Use the formula

(a) Step Deviation Method

Steps:

• Take mid value of group X.

• Take some assumed mean (A)

• Deduct A from x to get

• Take common factor (i) from amongst value of dx.

• Divide each value of dx by this factor to get

• Multiply by f to get

• Take sum of all value of to obtain

• Use the formula

## Weighted Arithmetic Mean

Number certain weighting factors or weights depending on the significance attached to the numbers. At that time we calculate mean is called weighted mean.

Formula

• Easy and simple computation.

• Based on all observations of the series.

• Easily understood average.

• Treated as algebraically.