## Variance and Standard deviation for grouped data calculator

Use Variance and Standard Deviation for Grouped Data calculator to calculate sample mean,sample variance and sample standard deviation for grouped data based on data provided in class groups and frequencies. Below artile on standard deviation for grouped data calculator provides step by step procedure about how to use variance for grouped data calculator with detailed standard deviation for grouped data examples.

## Calculator

Variance and standard deviation for grouped data Calculator
Type of Frequncy Distribution DiscreteContinuous
Enter the Classes for X (Separated by comma,)
Enter the frequencies (f) (Separated by comma,)
Results
Number of Observations (n):
Sample Mean : ($\overline{x}$)
Sample variance : ($s^2_x$)
Sample Standard Deviation : ($s_x$)

### How to use Variance and Standard Deviation for Grouped Data Calculator?

Step 1 - Select type of frequency distribution (Discrete or continuous)

Step 2 - Enter the Range or classes (X) seperated by comma (,)

Step 3 - Enter the Frequencies (f) seperated by comma

Step 4 - Click on “Calculate” button to calculate sample standard deviation for grouped data

Step5 - Gives output as number of observation (n)

Step 6 - Calculate Sample mean ($\overline{x}$)

Step 7 - Calculate Sample Variance ($s^2_x$)

Step 8 - Calculate Sample Standard Deviation for Grouped Data ($s_x$)

## Variance and standard deviation for grouped data

Let $(x_i,f_i), i=1,2, \cdots , n$ be the observed frequency distribution.

## Sample Variance Calculation

The sample variance of $X$ is denoted by $s_x^2$ and is given by

$s_x^2 =\dfrac{1}{N-1}\sum_{i=1}^{n}f_i(x_i -\overline{x})^2$

OR

$s_x^2 =\dfrac{1}{N-1}\bigg(\sum_{i=1}^{n}f_ix_i^2-\frac{\big(\sum_{i=1}^n f_ix_i\big)^2}{N}\bigg)$

where,

• $N=\sum_{i=1}^n f_i$ is the total number of observations,
• $\overline{x}$ is the sample mean.

## Sample Standard Deviation for Grouped Data Calculation

The sample standard deviation of $X$ is defined as the positive square root of sample variance. The sample standard deviation of $X$ is given by

$s_x =\sqrt{s_x^2}$

Below are solved examples on Variance and Standard Deviation for Grouped Data to understand how to calculate sample mean, sample variance and sample standard deviation.

## Variance and standard deviation for grouped data Example 1

Following tables shows a frequency distribution of daily number of car accidents at a particular cross road during a month of April.

No.of car accidents ($x$) 2 3 4 5 6
No. of days ($f$) 9 11 6 3 1

Calculate variance and standard deviation of number of car accidents.

### Solution

$x_i$ $f_i$ $f_i*x_i$ $f_ix_i^2$
2 9 18 36
3 11 33 99
4 6 24 96
5 3 15 75
6 1 6 36
Total 30 96 342

Step 1 - Sample mean

The sample mean of $X$ is

\begin{aligned} \overline{x} &=\frac{1}{n}\sum_{i=1}^n f_ix_i\\ &=\frac{96}{30}\\ &=3.2\text{ accidents } \end{aligned}

The average of no.of car accidents is $3.2$ accidents .

Step 2 - Sample variance

Sample variance of $X$ is

\begin{aligned} s_x^2 &=\dfrac{1}{n-1}\bigg(\sum_{i=1}^{n}f_ix_i^2-\frac{\big(\sum_{i=1}^n f_ix_i\big)^2}{n}\bigg)\\ &=\dfrac{1}{29}\bigg(342-\frac{(96)^2}{30}\bigg)\\ &=\dfrac{1}{29}\big(342-\frac{9216}{30}\big)\\ &=\dfrac{1}{29}\big(342-307.2\big)\\ &= \frac{34.8}{29}\\ &=1.2 \end{aligned}

Step 3 - Sample standard deviation for grouped data

The standard deviation is the positive square root of the variance.

The sample standard deviation for grouped data calculated as

\begin{aligned} s_x &=\sqrt{s_x^2}\\ &=\sqrt{2.5}\\ &=1.0954 \text{ accidents } \end{aligned}

Thus the standard deviation of no.of car accidents is $1.0954$ accidents.

## Variance and standard deviation for grouped data Example 2

The table below shows the total number of man-days lost to sickness during one week’s operation of a small chemical plant.

Days Lost 1-3 4-6 7-9 10-12 13-15
Frequency 8 7 10 9 6

Calculate the variance and standard deviation of the number of lost days.

### Solution

Class Interval Class Boundries mid-value ($x_i$) Freq ($f_i$) $f_i*x_i$ $f_ix_i^2$
1-3 0.5-3.5 2 8 16 32
4-6 3.5-6.5 5 7 35 175
7-9 6.5-9.5 8 10 80 640
10-12 9.5-12.5 11 9 99 1089
13-15 12.5-15.5 14 6 84 1176
Total 40 314 3112

Step 1 - Sample mean

The sample mean of $X$ is

\begin{aligned} \overline{x} &=\frac{1}{N}\sum_{i=1}^n f_ix_i\\ &=\frac{314}{40}\\ &=7.85\text{ days } \end{aligned}

The average of total number of man days lost is $7.85$ days .

Step 2 - Sample Variance

Sample variance of $X$ is

\begin{aligned} s_x^2 &=\dfrac{1}{N-1}\bigg(\sum_{i=1}^{n}f_ix_i^2-\frac{\big(\sum_{i=1}^n f_ix_i\big)^2}{N}\bigg)\\ &=\dfrac{1}{39}\bigg(3112-\frac{(314)^2}{40}\bigg)\\ &=\dfrac{1}{39}\big(3112-\frac{98596}{40}\big)\\ &=\dfrac{1}{39}\big(3112-2464.9\big)\\ &= \frac{647.1}{39}\\ &=16.5923 \end{aligned}

Step 3 - Sample standard deviation for grouped data

The standard deviation for grouped data is the positive square root of the variance.

The sample standard deviation for grouped data calculated as

\begin{aligned} s_x &=\sqrt{s_x^2}\\ &=\sqrt{22.5}\\ &=4.0734 \text{ days } \end{aligned}

Thus the standard deviation of total number of man days lost is $4.0734$ days .

I hope, you may like above article on Variance and Standard Deviation for Grouped Data Calculator with step by step guide on how to use variance for grouped data calculator with supportive examples to help you.