Calculation of Bell Curve Chart

To create a bell curve chart for the employees we need to calculate the mean, standard deviation and normal distribution.

Let’s create a bell curve chart for the following data.

Employee

Overall Score

Richard

4.5

Sam

3.3

John

2.8

Leo

4.6

Royce

4.3

Step 1: Calculate the Mean for all the values in the overall score column.

Mean = 3.9

Step 2: Calculate the standard deviation for all the values in the overall score column.

Standard deviation = STDEV.P(overall_score)

Standard Deviation = 0.71

Step 3: Based on the mean and standard deviation values, we have to define the distribution range.

Distribution Range

Data

(Mean-(3*S.D))

1.7450058

(Mean-(2*S.D))

2.4633372

(Mean-(1*S.D))

3.1816686

Mean

3.9

(Mean+(1*S.D))

4.6183314

(Mean+(2*S.D))

5.336628

(Mean+(3*S.D))

6.0529942

Step 4: Calculate the normal distribution for each value in the range.

Function in Google Sheet: Value =NORM.DIST(Distribution range, Mean, Standard_deviation,FALSE)

Range

Normal Distribution

1.7

0.006169643166

2.5

0.07516164061

3.2

0.3368511032

3.9

0.5553735789

4.6

0.3368511032

5.3

0.07516164061

6.1

0.006169643166

Step 5: Construct a bell-curve chart based on the values in the range and normal distribution.

The bell curve chart is available in 

• The overview section of the reports page in a 360 assessment.
• Custom widget in the overview section of 360 assessment.
• Team dashboard in the Portal.

Now Let's see some FAQ's : 

1. What will happen if all the employees are scored equally?

The bell curve will not be shown as the standard deviation becomes zero.

2. What will happen if only one subject has taken the assessment?

  The bell curve is constructed based on comparing the values so more than one subject has to be part of the assessment to visualize the chart.

3. Why does the x-axis on the bell curve show values less/more than the rating scale? 

As mentioned above, the x-axis on the bell curve is plotted based on the standard deviation values, so the values could be more or less than the rating scale.

4. What is the score distribution section? 

Score distribution shows the number of employees whose scores are present in the given range of values.

5) Sometimes, the distribution is above or below the rating scale; does that mean the employees have scored more than the rating scale?

No, we’re just showing the number of employees who fall within the given range, and they will not have a score above or below the rating scale.