LEARNING WITH MINITAB Chapter 8 - Laura Mae Williams

LEARNING WITH MINITAB

Chapter 8 SESSION ONE: MINITAB BASICS

MOREHEAD STATE UNIVERSITY

IET603: STATISTICAL QUALITY ASSURANCE IN SCIENCE AND TECHNOLOGY

DR. AHMAD ZARGARI

22 MARCH 2014

Laura M Williams, RN, CLNC, MSN

“THE STORY OF POPLAR CLONE 252”

~ A PRACTICAL USE FOR MINITAB ~

MINITAB allows for data analysis on various projects.

In this example, researchers have employed a data analyst to

determine how Poplar trees from genetically identical cells grow

in different environments:

SITE 1 SITE 2

by a creek with rich well-drained soil dry, sandy soil

GETTING STARTED … START MINITAB & OPEN A WORKSHEET

SO MANY CHOICES …

Dozens of worksheets are included in the MINITAB software in the DATA folder …

Make sure :

the file type is a MINITAB worksheet (*.mtw)

the current subdirectory is DATA

select Poplar1

HINT: Click on this tab

SELECTING THE DATA FILE

Allow data from Poplar1 Worksheet

to be added to your current

worksheet …

… and you will have pre-entered data to work with!

MORE DATA ?

15 observations were provided on the worksheet

5 more observations just became available …

DATA can be entered from the keyboard:

position the active cell is on the next available line and enter the additional data

PATTERNED DATA …

Let’s create a variable (“SITE”) which will indicate if the observation was

from “Environment 1” or from “Environment 2” …

Choose Calc Make Patterned Data Simple Set of Numbers

STORE THE PATTERNED DATA …

The new variable (called “SITE”) will have ten 1’s followed by ten 2’s

MINITAB will automatically assign “SITE” to

the next available cell … in this case, C4

To indicate the beginning and end of the

sequence, type “1” in “from first value” and

type “2” in “to last value”

Since we have ten 1’s and ten 2’s, in “List

each value,” type “10”

CLICK OK

A NEW COLUMN …

A new Site column appears in the active window.

Now …. this is a good time to save our project!

Choose: File Save Project

Enter File Name: POPLAR1

Click SAVE

When prompted to replace

existing file, click YES

COMPUTING DESCRIPTIVE STATISTICS

Stat Basic Statistics Display Descriptive Statistics

SEPARATE SUMMARY TABLES

We’re going to create separate summary tables for the trees at each site

describing the three variables: diameter, height, and weight.

Highlight the 3 variables and click select

SEPARATION BY SITE

To separate the statistics by site, select C4 SITE for the window

designated for “By Variable”

OPPORTUNITY TO CREATE A GRAPH

Click Graph to select from 4 display options

GRAPH SELECTION

Select “Boxplot of Data” and click OK for both windows

THE NUMBERS

MINITAB will separate the data by

the three variables, and will again

separate the individual variable

statistics by the site

THE PICTURES

Because we selected a visual representation, MINITAB also

displays the graph selected – making it very easy to see that SITE

2 is producing thicker, taller, and heavier Poplar trees

A RECAP

So far, this is what we have done ….

NOW FOR THE MATH …

The researchers have to predict how much the trees will weigh:

Based on previous work, they know that a tree’s weight is closely related to

the square of its diameter multiplied by its height

Researchers already have height and diameter data to predict a NEW variable

The new variable will be called “D2H” for

diameter squared times height

In Expression, type C1**2*C2 (tells MINITAB to square the variable Diameter (C1), multiply by the

variable Height (C2), and store the result in a new variable called D2H)

THE NEW DATA WINDOW

New column C5 added, showing prediction calculations made …

ORDERING THE SCATTERPLOT

Another graph is needed at this point to provide an easy to interpret

visual showing the correlation between the current weight and the

predicted weight.

Choose Graph Scatterplot THEN

Select the desired Scatterplot

Enter the Y and X Variables

THE SCATTERPLOT

140120100806040200

1.2

1.0

0.8

0.6

0.4

0.2

0.0

D2H

We

igh

tScatterplot of Weight vs D2H

unusual data point

IS THERE A CORRELATION ?

Back to the basics ….

Stat Basic Statistics Correlation

In Variables, enter Weight AND D2H

Click OK

SESSION WINDOW OUTPUT

The correlation coefficient measures the linear relationship between two variables and assumes

a value between -1 and +1. The high POSITIVE correlation coefficient of 0.913 is close to 1,

showing a strong relationship between Weight and D2H for the trees in this sample.

NOW – LET’S EDIT THE SESSION WINDOW

FOR AN APPROPRIATE REPORT

Select Editor and make sure that the session

window can be edited

CLEAN UP THE SESSION WINDOW

Delete ALL the text not relevant to a report

Insert appropriate comments for identification

THE FINAL PRODUCT

THAT’S A WRAP… SAVE IT – PRINT IT – CLOSE IT

SAVE IT!!!

PRINT IT:

File Print Session

AND

Window Manage Graphs

Select the 4 graphs

Click Print

Click OK

CLOSE IT