a normal distribution whenever the sample size (n) is 30 or more

It is believed that a normal distribution is reached when the sample size is 30 or more. The normal distribution is based on the Central Limit Theorem, which states that when a sample size (n) is large enough, the frequencies of the sample values should form a normal distribution regardless of the type of original population distribution. With a sample size of 30 or more, the normal distribution is likely to hold true because the large sample size will provide a good representation of the original population distribution.