# Chapter 5 Some Key Ingredients for Inferential Statistics: The Normal Curve, Probability, and Population Versus Sample.

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Chapter 5 Some Key Ingredients for Inferential Statistics: The Normal Curve, Probability, and Population Versus Sample

The Normal Distribution
Normal curve

The Normal Distribution
Normal curve and percentage of scores between the mean and 1 and 2 standard deviations from the mean

The Normal Distribution
The normal curve table and Z scores Gives the precise percentage of scores between the mean (Z score of 0) and any other Z score Table lists positive Z scores

The Normal Distribution
Steps for figuring the percentage above of below a particular raw or Z score: 1. Convert raw score to Z score (if necessary) 2. Draw normal curve, where the Z score falls on it, shade in the area for which you are finding the percentage 3. Make rough estimate of shaded area’s percentage (using 50%-34%-14% rule)

The Normal Distribution
Steps for figuring the percentage above of below a particular raw or Z score: 4. Find exact percentage using normal curve table 5. If needed, add or subtract 50% from this percentage 6. Check the exact percentage is within the range of the estimate from Step 3

The Normal Distribution
Steps for figuring Z scores and raw scores from percentages: 1. Draw normal curve, shade in approximate area for the percentage (using the 50%-34%-14% rule) 2. Make rough estimate of the Z score where the shaded area starts 3. Find the exact Z score using the normal curve table

The Normal Distribution
Steps for figuring Z scores and raw scores from percentages: 4. Check that your Z score is similar to the rough estimate from Step 2 5. If you want to find a raw score, change it from the Z score

Probability Probability Outcome
Expected relative frequency of a particular outcome Outcome The result of an experiment

Probability Range of probabilities Probabilities as symbols
Proportion: from 0 to 1 Percentages: from 0% to 100% Probabilities as symbols p p < .05 Probability and the normal distribution Normal distribution as a probability distribution

Sample and Population Population Sample Methods of sampling
Random selection Haphazard selection

Sample and Population Population parameters and sample statistics

Controversies and Limitations
Is the normal curve really so normal What does probability really mean? Sample and population

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