Class distribution is considered to be normal using normal approximation to binomial.
A frequency distribution is a table that shows classes or intervals of data with a count of the number in each class.
Given :
In a city with a population of 1 million
i.e Population size (N) = 1 million = 1000000
From which 500 people have been diagnosed with cancer
Let X : No. of people have been diagnosed with cancer
X = 500
Population proportion (p) :
p = XNp =5001000000p = 0.0005
So , the proportion of people who do not have cancer (q)=1-p
=1-0.0005
=0.9995
Here the distribution of X is Binomial
Such that :
i. No. of trials are fixed
ii. Probability of success is constant (p=0.0005)
iii. Possible outcomes are two (having cancer or not)
Here we can use normal approximation to Binomial
Because N is very large
So class distribution is considered to be normal using normal approximation to binomial.
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