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

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Presentation on theme: "Chapter 5 Some Key Ingredients for Inferential Statistics: The Normal Curve, Probability, and Population Versus Sample."— Presentation transcript:

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

2 The Normal Distribution Normal curve

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

4 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

5 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 areas percentage (using 50%-34%-14% rule)

6 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

7 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

8 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

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

10 Probability Range of probabilities –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

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

12 Sample and Population Population parameters and sample statistics

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


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