《统计学基础(英文版·第7版)》教学课件les7e05 01.pptx

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1、Chapter,Normal Probability Distributions,5,ChapterNormal Probability Dist,Chapter Outline,Chapter Outline,Section 5.1,Introduction to Normal Distributions and the Standard Normal Distributions,Section 5.1Introduction to Nor,Section 5.1 Objectives,How to interpret graphs of normal probability distrib

2、utionsHow to find areas under the standard normal curve,Section 5.1 ObjectivesHow to i,Properties of a Normal Distribution,Continuous random variable Has an infinite number of possible values that can be represented by an interval on the number line.Continuous probability distributionThe probability

3、 distribution of a continuous random variable.,.,The time spent studying can be any number between 0 and 24.,Properties of a Normal Distrib,Properties of a Normal Distribution,.,Normal distribution A continuous probability distribution for a random variable, x. The most important continuous probabil

4、ity distribution in statistics.The graph of a normal distribution is called the normal curve.,Properties of a Normal Distrib,Properties of a Normal Distribution,.,The mean, median, and mode are equal.The normal curve is bell-shaped and is symmetric about the mean.The total area under the normal curv

5、e is equal to one.The normal curve approaches, but never touches the x-axis as it extends farther and farther away from the mean.,Total area = 1,Properties of a Normal Distrib,Properties of a Normal Distribution,.,Between and + (in the center of the curve), the graph curves downward. The graph curve

6、s upward to the left of and to the right of + . The points at which the curve changes from curving upward to curving downward are called the inflection points.,Properties of a Normal Distrib,Probability Density Function (PDF),.,A discrete probability distribution can be graphed with a histogram. For

7、 a continuous probability distribution, you can use a probability density function (pdf). A probability density function has two requirements:the total area under the curve is equal to 1 the function can never be negative.,Probability Density Function (,Means and Standard Deviations,A normal distrib

8、ution can have any mean and any positive standard deviation.The mean gives the location of the line of symmetry.The standard deviation describes the spread of the data.,Means and Standard DeviationsA,Example: Understanding Mean and Standard Deviation,.,Which curve has the greater mean?,Solution:Curv

9、e A has the greater mean (The line of symmetry of curve A occurs at x = 15. The line of symmetry of curve B occurs at x = 12.),Example: Understanding Mean an,Example: Understanding Mean and Standard Deviation,.,Which curve has the greater standard deviation?,Solution:Curve B has the greater standard

10、 deviation (Curve B is more spread out than curve A.),Example: Understanding Mean an,Example: Interpreting Graphs of Normal Distributions,.,The scaled test scores for New York State Grade 4 Common Core Mathematics Test are normally distributed. The normal curve shown below represents this distributi

11、on. What is the mean test score? Estimate the standard deviation of this normal distribution. (Adapted from New York State Education Department),Example: Interpreting Graphs o,Solution:The scaled test scores for the New York State Grade 4 Common Core Mathematics Test are normally distributed with a

12、mean of about 305 and a standard deviation of about 40.,Solution: Interpreting Graphs of Normal Distributions,.,Solution:Solution: Interpretin,Solution:Using the Empirical, you know that about 68% of the scores are between 265 and 345, about 95% of the scores are between 225 and 385, and about 99.7%

13、 of the scores are between 185 and 425.,Solution: Interpreting Graphs of Normal Distributions,.,Solution:Solution: Interpretin,The Standard Normal Distribution,.,Standard normal distribution A normal distribution with a mean of 0 and a standard deviation of 1.,Any x-value can be transformed into a z

14、-score by using the formula,The Standard Normal Distributi,The Standard Normal Distribution,.,The standard normal distribution is a normal distribution with a mean of 0 and a standard deviation of 1. The total area under its normal curve is 1.,The Standard Normal Distributi,Properties of the Standar

15、d Normal Distribution,.,The cumulative area is close to 0 for z-scores close to z = 3.49.The cumulative area increases as the z-scores increase.,Properties of the Standard Nor,Properties of the Standard Normal Distribution,.,The cumulative area for z = 0 is 0.5000.The cumulative area is close to 1 f

16、or z-scores close to z = 3.49.,Properties of the Standard Nor,Example: Using The Standard Normal Table,.,Find the cumulative area that corresponds to a z-score of 1.15.,The area to the left of z = 1.15 is 0.8749.,Move across the row to the column under 0.05,Solution:Find 1.1 in the left hand column.

17、,Example: Using The Standard No,Example: Using The Standard Normal Table,.,Find the cumulative area that corresponds to a z-score of 0.24.,Solution:Find 0.2 in the left hand column.,Move across the row to the column under 0.04.,The area to the left of z = 0.24 is 0.4052.,Example: Using The Standard

18、No,Finding Areas Under the Standard Normal Curve,.,Sketch the standard normal curve and shade the appropriate area under the curve.Find the area by following the directions for each case shown.To find the area to the left of z, find the area that corresponds to z in the Standard Normal Table.,The ar

19、ea to the left of z = 1.23 is 0.8907,Use the table to find the area for the z-score,Finding Areas Under the Standa,Finding Areas Under the Standard Normal Curve,.,To find the area to the right of z, use the Standard Normal Table to find the area that corresponds to z. Then subtract the area from 1.,

20、Subtract to find the area to the right of z = 1.23: 1 0.8907 = 0.1093.,The area to the left of z = 1.23 is 0.8907.,Use the table to find the area for the z-score.,Finding Areas Under the Standa,Finding Areas Under the Standard Normal Curve,.,To find the area between two z-scores, find the area corre

21、sponding to each z-score in the Standard Normal Table. Then subtract the smaller area from the larger area.,Finding Areas Under the Standa,Example: Finding Area Under the Standard Normal Curve,.,Find the area under the standard normal curve to the left of z = 0.99.,From the Standard Normal Table, th

22、e area is equal to 0.1611.,Solution:,Example: Finding Area Under th,Example: Finding Area Under the Standard Normal Curve,.,Find the area under the standard normal curve to the right of z = 1.06.,From the Standard Normal Table, the area is equal to 0.1446.,Solution:,Example: Finding Area Under th,Ex

23、ample: Finding Area Under the Standard Normal Curve,.,Find the area under the standard normal curve between z = 1.5 and z = 1.25.,From the Standard Normal Table, the area is equal to 0.8276. So, 82.76% of the area under the curve falls between z = 1.5 and z = 1.25.,Solution:,Example: Finding Area Under th,