By Suha Tayyab
BIOSTATISTICS- NORMAL DISTRIBUTION CURVE
The normal distribution curve, also known as the Gaussian curve or the bell curve, is used to illustrate continuous data. For example, heights, blood pressure, weight, test scores, etc.
It is characterized by the following:
1. Bell Shaped curve
2. Asymptotic (either end of the curve does not touch the x-axis)
3. Bilaterally symmetrical
4. Total area under the curve is one
5. The Mean, median, mode is numerically equal and equal to zero
6. Standard Deviation (SD) rule of
1SD=68% (μ +/-34.1%)
68% of the data falls within one standard deviation of the mean.
2SD=95% (μ +/47.5%)
95% of the data falls within two standard deviations of the mean.
3SD=99.7% (μ +/49.6%)
99.7% of the data falls within three standard deviations of the mean.
7. Mean is denoted by mu (μ) and standard deviation by sigma (σ)
To plot this curve using a data set, the data set need to be standardized. This simply means that the mean and standard deviation of the data set will be calculated. Standardizing would me that the value of the mean would be equal to zero and the value of standard deviation would be equal to 1. The rest of the data values will also be standardized using the following formula to calculate z values.
And corresponding values on a normal distribution table will be used to plot this graph.
In practice, a large volume of data is collected from experiments or researches, and to analyse and apply these functions, applications like Microsoft Excel, SPSS are used.
We will work with sample data in excel and generate a normal distribution curve. Before we begin, we will talk about what Microsoft Excel is.
Microsoft Excel is spreadsheet software used to organize data in rows and columns. It is used to perform various mathematical and statistical functions to the data.
Step 1: Calculate Mean and Standard deviation of data of interest
Step 2 Calculate z value using the formula given
Step 3: Calculate normal distribution values
Step 4: Insert an area graph
