Minitab assignment in statistic class
Minitab assignment in statistic class
I need some one who can do this assignment for me in the minitab
Frequently it is assumed that a population has a normal distribution. We can use normal probability plots to verify whether the normal assumption is valid. If the normal probability plot is a straight line, the population is approximately normal; otherwise the population is not normal. In this exercise you will display the normal probability plot for three distributions. The first is sampled from a normal distribution and the other two are highly skewed distributions. Copy and paste the graphs obtained following the instructions below into a Word document, label them, and answer the questions in the same document. Print and attach your Minitab session window.
Minitab Commands:
1. Generate a sample of size 200 from a Normal distribution with mean 7 and standard deviation 2, compare the sample mean and sample standard deviation with the population mean and standard deviation:
Calc > Random Data > Normal… Enter 200 as the number of rows. Store those values into C1. Choose 7 as the mean and 2 as the standard deviation. Click OK and enter Normal as the column title (under C1 in the worksheet).
Stat > Basic Statistics > Display Descriptive Statistics for C1. Produce a graph to examine the shape of the distribution:
Graph > Dotplot > Simple. Graph C1.
Generate the nscores of the sample and the normal probability plot. If the sample came from a normal distribution, the plot should be roughly linear:
Calc > Calculator. Store the results into C11 and enter the expression NSCORES(C1) .
Graph > Scatterplot > Simple. Plot C1 versus C11. Select C11 as the Y variable and C1 as the X
variable.
2. Transform the data to produce a sample from a population that is not normal but skewed to the right:
Calc > Calculator. Store the results into C2 and enter the expression EXP(C1/3). Enter SkewRgt as title of C2.
Compare the mean of C1 with the mean of C2:
Stat > Basic Statistics > Display Descriptive Statistics for C2. Notice that mean (C2) E^(mean C2/3).
Examine the shape of this distribution. Obtain the normal probability plot of this skewed distribution and compare it with the normal probability plot from step 1:
Graph > Dotplot > Simple. Graph C2.
Calc > Calculator. Store the results into C12 and enter the expression NSCORES(C2).
Graph > Scatterplot > Simple. Plot C2 versus C12. Select C12 as the Y variable and C2 as the X variable.
3. Transform the data to produce a sample from a population that is not normal but skewed to the left:
Calc > Calculator. Store the results into C3 and enter the expression LOG (C1). Enter SkewLft as title of C3.
Stat > Basic Statistics > Display Descriptive Statistics for C3.
Examine the shape of this distribution. Obtain the normal probability plot of this skewed distribution and compare it with the normal probability plots from step 1 and step 2:
Graph > Dotplot > Simple. Graph C3
Calc > Calculator. Store the results into C13 and enter the expression NSCORES(C3).
Graph > Scatterplot > Simple. Plot C3 versus C13. Select C13 as the Y variable and C3 as the X variable.
Questions:
Based on your Minitab output, answer the following questions using complete sentences. Do not draw graphs. You may use terms such as convex or concave.
a) Does the graph for the variable ‘Normal’ look like a smooth bell-shaped curve? Is the normal probability plot a relatively straight line?
b) What are the values of population mean and standard deviation of the variable ‘Normal’? What are the values for the randomly generated data?
c) What shape does the normal probability plot have when a variable comes from a distribution that is skewed to the right? What is the shape of the dotplot?
d) What shape does the normal probability plot have when a variable comes from a distribution that is skewed to the left? What is the shape of the dotplot?
It is okay to discuss computer work with others. However, when it comes time for the write-up, ALL WORK IS TO BE STRICTLY YOUR OWN.
