# How to Calculate the Standard Deviation of a Sample

The standard deviation (SD) is a statistical measure that helps determine the dispersion or spread of data points within a dataset. By calculating the standard deviation, one can gain insight into how the data points deviate from the mean or average, providing useful information about the variability and distribution of the data. In this article, we will discuss how to calculate the standard deviation of a sample using step-by-step calculations.

**Steps to Calculate the Standard Deviation of a Sample**

**1. Add up all data points in your sample:**

The first step in calculating the standard deviation is to sum up all the data points within your sample. This summation will allow you to compute for the mean later.

Example: Suppose you have a dataset: {5, 7, 11, 15, 18}

ΣX = 5 + 7 + 11 + 15 + 18 = 56

**2. Determine the size (n) and mean (μ) of your dataset:**

Calculate the total number of data points (n) and then compute for their mean (μ) by dividing the sum of all data points by n.

n = number of data = 5

Mean (μ) = ΣX / n = (56 / 5) = 11.2

**3. Calculate deviations from the mean (μ):**

Subtract the mean from each data point in your dataset. This gives you individual deviations from the mean.

Deviation = X – μ

{5-11.2, 7-11.2, 11-11.2, 15-11.2, 18-11.2} = {-6.2, -4.2, -0.2, 3.8, 6.8}

**4. Square each deviation:**

Next, square each deviation that you obtained in the previous step.

{(-6.2)^2, (-4.2)^2, (-0.2)^2, (3.8)^2, (6.8)^2} = {38.44, 17.64, 0.04, 14.44, 46.24}

**5. Calculate the sum of squared deviations:**

Add all squared deviations from step 4.

ΣSquaredDev = 38.44 + 17.64 + 0.04 + 14.44 + 46.24 = 116.8

**6. Determine the variance:**

Next, divide the sum of squared deviations by n -1; where (n -1) represents the degrees of freedom.

Variance (σ^2) = ΣSquaredDev / (n -1) = 116.8 / (5 -1) = 116.8 / 4 = 29.2

**7.Compute the standard deviation:**

Lastly, calculate for standard deviation by taking the square root (√) of the variance.

Standard Deviation (σ) = √Variance = √29.2 ≈ 5.4

**Conclusion:**

With a calculated standard deviation of approximately 5.4 for our example dataset, we can now understand better how these data points deviate from their mean value of 11.2 and how dispersed they are within the dataset thus assisting in analyzing data patterns and making informed predictions or decisions based on variability insights achieved through standard deviation calculations.