Descriptive Statistics II: By the end of this class you should be able to:

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Descriptive Statistics II: By the end of this class you should be able to:. describe the meaning of and calculate the mean and standard deviation of a sample estimate normal proportions based on mean and standard deviation plot a histograms with alternative scaling. Palm: Section 7.1, 7.2.

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Descriptive Statistics II:By the end of this class you should be able to:
• describe the meaning of and calculate the mean and standard deviation of a sample
• estimate normal proportions based on mean and standard deviation
• plot a histograms with alternative scaling

Palm: Section 7.1, 7.2

Exercise
• Read into MATLAB
• Prepare a single figure with two plots
• a histogram of March highs (row 2)
• a histogram of April highs (row 4)
• Label these plots fully
• Print out the your commands and the resulting figure
Review: Quantifying Variation

Mean

Central Tendency

>> mean(x)

Standard Deviation

>> std(x)

difference  deviation of each point about the mean

squared  all values positive

Summation  yields one number

Divide by n-1 normalize the sum for based on degrees of freedom

The Normal (Gaussian) Distribution

Mode

(Population)

Standard

Deviation

Mean

meanm

Percentage of observations in the given range

68 %

 1s

95.5 %

99.7%

 2s

 3s

Expected Proportions for known 
Proportions Problem

Data analysis of the breaking strength of a certain fabric shows that it is normally distributed with a mean of 200 lb and a variance (2) of 9.

• Estimate the percentage of fabric samples that will have a breaking strength between 197 lb and 203 lb.
• Estimate the percentage of fabric samples that will have a breaking strength no less than 194 lb.
• Look at a histogram of the second set of data, ‘cord2’
• How would you compare it to cord the first set of data?
• What problems do you run into?