엑셀의 정규분포 함수

NORMDIST(x, mean, standard_dev, cumulative)

NORMDIST gives the probability that a number falls at or below a given value of a normal distribution.

• x -- The value you want to test.
   
• mean -- The average value of the distribution.
   
• standard_dev -- The standard deviation of the distribution.
   
• cumulative -- If FALSE or zero, returns the probability that x will occur; if TRUE or non-zero, returns the probability that the value will be less than or equal to x.

Example: The distribution of heights of American women aged 18 to 24 is approximately normally distributed with a mean of 65.5 inches (166.37 cm) and a standard deviation of 2.5 inches (6.35 cm). What percentage of these women is taller than 5' 8", that is, 68 inches (172.72 cm)?

The percentage of women less than or equal to 68 inches is:

=NORMDIST(68, 65.5, 2.5, TRUE)  =  84.13%

Therefore, the percentage of women taller than 68 inches is 1 - 84.13%, or approximately 15.87%. This value is represented by the shaded area in the chart above.

STANDARDIZE(x, mean, standard_dev)

STANDARDIZE returns the z value for a specified value, mean, and standard deviation.

To illustrate, in the NORMINV example above, we found that a woman would need to be at least 63.81 inches tall to avoid the bottom 25% of the population, by height. The STANDARDIZE function tells us that the z value for 63.81 inches is:

=STANDARDIZE(63.81, 65.5, 2.5)  =  -0.6745

We can check this number by using the NORMSDIST function:

=NORMSDIST(-0.6745) = 25%

That is, a z value of -.6745 has a probability of 25%.

[참고자료]

마이크로소프트 엑셀 지원 페이지

https://support.office.com/ko-kr/article/normdist-%ED%95%A8%EC%88%98-126db625-c53e-4591-9a22-c9ff422d6d58