Normal Distributions and Standard Scores - BNS 301

normal distribution

measures the central tendency as a symmetrical bell curve where most scores are towards the center

standard scores

scores that allow for comparison across different groups on populations by placing scores on a common axis

z score

a score that describes the relationship of a score to the distribution of all measured scores that uses both the mean and standard deviation

standard normal distribution

plotted z scores with a mean of zero and a SD of +-1

3 sigma rule of standard normal distribution

approximately 68% of data falls within +-SD, 95% within +-2SD and 99% within +-3D

central limit theorem

the distribution of the sample mean is always normal if the underlying data are normal. A sample mean with n > 30 will always be normally distributed even if underlying data isn’t.

positive z score

data is to the left of the score

negative z score

data is to the right of the z score