Python for Data Science: Laboratory Programs in Python

Statistical description of data without libraries

Laboratory Programs in Python

Python for Data Science: Laboratory Programs in Python: Descriptive Analytics: Statistical description of data without libraries

Normal distribution formula

Mathematically the Probability Density Function (PDF) of normal distribution is


where:

x = Value in the dataset

μ = Mean (average)

σ = Standard deviation (Spread of data)

e = Euler's number (≈ 2.718)


Ex 1.

A random variable X follows a normal distribution with mean of 10 and a standard deviation of 2. Find the value of the Probability Density Function (PDF) at x = 12.

Solution: The formula for finding PDF is


Given that:

(μ = 10, σ = 2, x = 12):


Simplify the exponent:

[(12‒10)] / 2.22    = 4/8  =  0.5

The formula now becomes

f(12) =  [ 1 / 2√2π ] e ‒0.5

√2π   ≈  2.5066,

e‒0.5   ≈  0.6065.

f(12) = [1 / 2×2.5066 ] . 0.6065

          =  0.6065 / 5.0132   ≈ 0.1210

Hence, the value of the PDF at x = 12 is approximately 0.1210



Definition of z‒score:

Formula:

 (X ‒μ) / σ

where

X = Individual value

μ = Mean

σ = Standard deviation

 

Ex 2.

Consider Mean = 70, Standard deviation = 10, and student's score is 85. Calculate Z score and interpret your answer.

Solution :

The z score can be calculated as

 (X ‒μ) / σ = (85‒70) / 10

z = 1.5

Interpretation: The student scored is standard deviation above mean. That means this student has scored better than most of the students.

 

Ex 3.

Consider mean height = 165 cm, σ = 5 cm, X = 155 cm. Calculate z score and interpreter your result.

Solution :

z  = (155‒165) / 5  ‒2

Interpretation: The height is 2 standard deviations below mean. So the height of student is short as compared to average.


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Python for Data Science: Laboratory Programs in Python



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