AP Statistics : Chapter 2 - The Normal Distributions (Vocabulary)

density curve
A curve that describes the overall pattern of a distribution.
• is always on or above the horizontal axis
• has area exactly 1 beneath it
µ (mu)
mean of distribution
σ (sigma)
standard deviation of a density curve
The results of a chance experiment
Pretending to perform a chance experiment and coming up with fictitious but possible outcomes.
normal curve
Curves that are symmetric, single-peaked, and bell-shaped
normal distribution
Described by a normal curve in which the mean is located at the center of the symmetric curve and is the same as the median.
inflection point
The point at which a change of curvature takes place
68-95-99.7 rule
• 68% of the observations fall within one σ of the mean µ

• 95% of observations fall within 2 σ of the mean µ

• 99.7% of observations fall within 3 σ of the mean µ
The percent of the distribution that is at or lower than the observation
N (µ,σ)
normal distribution (with mean µ and standard deviation σ)
standardized value

observation (x) - mean (µ)
standard deviation (σ)
another name for standardized value; tells us how many standard deviations the original observation falls away from the mean and in which direction.
standard normal distribution
the normal distribution with mean 0 and standard deviation 1
normal probability plot
method of providing a good assessment of the adequacy of the normal model for a set of data