Mean, median and mode for grouped data
Let $(x_i,f_i), i=1,2, \cdots , n$ be given frequency distribution.
Formula
Sample mean
The mean of $X$ is denoted by $\overline{x}$ and is given by
$\overline{x} =\dfrac{1}{N}\sum_{i=1}^{n}f_ix_i$
In case of continuous frequency distribution, $x_i$’s are the mid-values of the respective classes.
Sample median
The median is given by
$\text{Median } = l + \bigg(\dfrac{\frac{N}{2} - F_<}{f}\bigg)\times h$
where
- $N$, total number of observations
- $l$, the lower limit of the median class
- $f$, frequency of the median class
- $F_<$, cumulative frequency of the pre median class
- $h$, the class width
Sample mode
The mode of the distribution is given by
$\text{Mode } = l + \bigg(\dfrac{f_m - f_1}{2f_m-f_1-f_2}\bigg)\times h$
where
- $l$, the lower limit of the modal class
- $f_m$, frequency of the modal class
- $f_1$, frequency of the class pre-modal class
- $f_2$, frequency of the class post-modal class
- $h$, the class width
