Lab3 - Lab 3 Assignment SOLUTION Due Wednesday, February...

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Knapp – Stat 350 Lab #3: Page 1 of 6 Lab 3 Assignment SOLUTION Due Wednesday, February 13, 2008 at the beginning of class. Use the data in the file Lab03.xls on the course webpage. For each of the 5 variables (var1, var2, var3, var4, var5) in the Excel file, give: a histogram of the sample data with a normal distribution fitted line the probability plot of this data. The probability plot must include the observed point values, the fitted line and the 95% confidence bounds for the fitted line. For each pair of graphs (each variable), answer the following questions. a. Looking just at the histogram, would you feel comfortable saying this sample came from a normal distribution? ( There really are no right or wrong answers – this is a judgment call, I just want you to think about it. ) b. Looking just at the probability plot (don't look at the information on the right side of the table), would you feel comfortable saying this sample came from a normal distribution? ( There really are no right or wrong answers – this is a judgment call, I just want you to think about it. ) c. According to the p-value on the probability plot, can we say this sample came from a normal distribution? d. If your answer to part (c) was "no", describe how the probability plot deviates from normal and compare this to how the histogram appears to deviate from the normal. It might help to also examine the original data.
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Knapp – Stat 350 Lab #3: Page 2 of 6 Var1 The actual distribution of these sample points is Normal( μ = 40, σ = 6) 52 48 44 40 36 32 4 3 2 1 0 var1 Frequency Mean 40.47 StDev 5.077 N1 4 Histogram of var1 Normal 60 50 40 30 20 99 95 90 80 70 60 50 40 30 20 10 5 1 var1 Percent Mean 40.47 StDev 5.077 4 AD 0.192 P-Value 0.874 Probability Plot of var1 Normal - 95% CI a. Looking just at the histogram, would you feel comfortable saying this sample came from a normal distribution? ( There really are no right or wrong answer – this is a judgment call, I just want you to think about it. ) Just looking at the histogram, it is hard to say – it might be from a normal distribution. b. Looking just at the probability plot (don't look at the information on the right side of the table), would you feel comfortable saying this sample came from a normal distribution? ( There really are no right or wrong answer – this is a judgment call, I just want you to think about it. ) The smallest value is pretty far from the line (but still within the confidence bounds) – all the other points are pretty close to the line. I don’t think the probability plot is convincing evidence that the sample is NOT from a normal distribution.
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This note was uploaded on 03/09/2010 for the course STAT 350 taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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Lab3 - Lab 3 Assignment SOLUTION Due Wednesday, February...

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