Calculates the width of half the confidence interval for a normal distribution.
CONFIDENCE(alpha, standard_deviation, pop_size)
alpha- One minus the desired confidence level. E.g.
0.9, or 90%, confidence.
standard_deviation- The standard deviation of the population.
pop_size- The size of the population.
CONFIDENCEcalculates the width of half the confidence interval such that a value picked at random from the data set has
1-alphaprobability of lying within the mean plus or minus the result of
ZTEST: Returns the one-tailed P-value of a Z-test with standard distribution.