If n=15 and P=0.1, would normal distribution provide accurate probabilities?
Continuous Probability Distributions
Probability distributions are of two types, which are continuous probability distributions and discrete probability distributions. A continuous probability distribution contains an infinite number of values. For example, if time is infinite: you could count from 0 to a trillion seconds, billion seconds, so on indefinitely. A discrete probability distribution consists of only a countable set of possible values.
Normal Distribution
Suppose we had to design a bathroom weighing scale, how would we decide what should be the range of the weighing machine? Would we take the highest recorded human weight in history and use that as the upper limit for our weighing scale? This may not be a great idea as the sensitivity of the scale would get reduced if the range is too large. At the same time, if we keep the upper limit too low, it may not be usable for a large percentage of the population!
- Normal to binomial approximation :
For a random variable with a Binomial distribution with parameters and , the population mean and population variance are computed as follows:
When the sample size is large enough, and/or when is close to , then is approximately normally distributed. But in order to approximate a Binomial distribution (a discrete distribution) with a normal distribution (a continuous distribution), a so called continuity correction needs to be conducted. Specifically, a Binomial event of the form
will be approximated by a normal event like :
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