# Statistics Ch 3

The flashcards below were created by user firefly501 on FreezingBlue Flashcards.

1. Density Curve
• Mathematical model of a distribution
• Total area under the curve is equal to 1, or 100%
• Normal distributions: symmetrical, bell- shaped density curves defined by a mean and a
• standard deviation.
2. Emprirical Rule
• About 68% of all observations are within 1 standard deviation
• of the mean.
• About 95% of all observations are within 2 standard deviations of the mean.
• Almost all (99.7%) observations are within 3 standard deviations of the mean.
3. z-score
• Standardize our data to transform any Normal curve N (μ, σ) into the standard Normal
• curve N (0,1).
• A z-score measures the number of standard deviations that a data value x is from the
• mean μ

z = (x -µ) / σ

• When x is larger than the mean, z is positive.
• When x is smaller than the mean, z is negative.
4. Standard Normal Probabilities
• Table A gives the area under the standard Normal curve to the left of any z-value.
• When you know the proportion, but you don’t know the x-value that represents the cutoff,
• you need to use Table A backward.
 Author: firefly501 ID: 137592 Card Set: Statistics Ch 3 Updated: 2012-02-25 16:49:52 Tags: statistics Folders: Description: The Normal Distributions Density curves, z- score, standard Normal probabilities (Table A) Show Answers: