Statistics Minitab Lab 2

The first thing you need to do today is to join onlineclasses.

To do this open up ‘internet explorer’ from the icon on your desktop and go to webpage www.onlineclasses.ucd.ie , then click on the icon: Click here to enter AUC (secure web site).

Your username is of the format: s03bf17z (do not include full stops or sci.bf.ucd).

Your password is the same one you used to log on to the computer.

Click on ‘customise my courses’. The course ID is STAT1001.

1. A Minitab worksheet called PULSE.MTW is to be found on the online class STAT1001 in a folder called 'Data Sets'. You have to download this file to the folder you created on your home directory last week called h:\minitab. This worksheet contains data on 92 students. Each student was asked to take his or her pulse rate and then to flip a coin. If the coin came up heads, the student was asked to run in place for one minute and to take their pulse rate again. If the coin come up tails they were asked to wait for one minute and then take their pulse rate again. Background information on each student regarding their regular activity was also recorded.

2. Use File-Open Worksheet to retrieve the MINITAB data set h:\minitab\PULSE.MTW.

The variables you will see are:

PULSE1 PULSE2 RAN SMOKES SEX HEIGHT WEIGHT ACTIVITY. Where:

PULSE1 first pulse

PULSE2 second pulse

RAN coded 1 or 2, indicating if the student ran or not

SMOKES 1=yes 2=no

SEX 1=male 2=female

HEIGHT height in inches

WEIGHT weight in pounds

ACTIVITY 1=low 2=moderate 3=high for level of normal physical activity of the student.

3. Clicking on Graph-Histogram and select PULSE1 then click on OPTIONS button and choose CutPoint to get a histogram display of PULSE1. Repeat this procedure with the option as Midpoint.

4. Produce a dotplot of the same data, Graph => Dotplot ( choose ‘PULSE1’ as your measurement variable). Can you locate the lowest and highest values? ______

5. Get a stem-and-leaf plot of PULSE1 by choosing Graph => Stem-and-Leaf. Can the above question now be answered more accurately? ______

6. The variable ‘PULSE2’ contains the pulse rates for students who ran for a minute or who did nothing for a minute. This depended on whether they got heads or tails. The variables ‘RAN’ records what each student did. Do you think this variable will have an effect on ‘PULSE2’? If it does it should be taken into account when looking at ‘PULSE2’.

Do a dot plot graph for the variable PULSE2. Click on Graph - Dotplot .

Repeat this procedure but this time choose RAN as the ‘by’ variable and compare the two outputs. What does the ‘by’ variable do? ______

Which value of ‘RAN’ do you think means that the student ran for one minute? ______

7. The next step is to unstack the information in ‘PULSE2’ into two variables, one for ‘RAN’=1 and the second for ‘RAN’=2. When this is done, we can then plot each separately. Click on Manip => Unstack Columns.... Enter ‘PULSE2’ as the variable we want to unstack, using subscripts in ‘RAN’. Click the option to unstack the data after the last column in use. i.e. C9 and C10, then click on OK. Scroll down though the data. You should see the two new variables, C9 and C10. Name these ‘RUN1’ and ‘RUN2’.

Calculate some summary statistics for RUN1 & RUN2 by typing this command in the session window (don't forget to enable commands):

MTB > Descriptive ‘RUN1’ ‘RUN2’

Does it look as if there is a difference between the means ? ______

How do the Mean and Median for RUN1 compare ? ______

Can you see why from the dotplot produced earlier ? ______

What about RUN2 ? ______

______

8. Now, plot a histogram of these two variables. Click on Graph - Histogram In the next window, select ‘RUN1’ in graph 1 and ‘RUN2’ in graph 2. Next, click on OPTIONS button and choose CutPoint click ok twice. You should see two histograms of the pulses when they ran and didn’t run. Do you think there is a difference between the two variables?

9. Produce a histogram of HEIGHT: Graph-Histogram, select HEIGHT, then click on OPTIONS and choose CutPoint as Type of Intervals.

Do you think HEIGHT will be affected by the variable SEX?

To see if it is, produce a dotplot of HEIGHT, using SEX as the by variable.

10. This can also be seen by getting descriptive statistics of HEIGHT by SEX. Go to the Stat > Basic Statistics > Display Descriptive Statistics..., select height as the variable of interest and sex as the 'By variable'.

(a) How do the means compare for SEX=1 and SEX=2? (which number is male? female?)

______

(b) How do the Mean and Median compare for SEX=1?

______

(c)ow do the Mean and Median compare for SEX=1?

______

(d) Does this correspond with the dotplots for SEX=1 and SEX=2?

______

11. Repeat (10.) for the variable WEIGHT and answer the same questions.

(a) ______

(b) ______

(c) ______

12. Produce a Stem-and-Leaf diagram of WEIGHT and use an increment of 5.

Locate the median from the stem-and-leaf diagram? ______

Check that you are correct by getting the descriptive statistics for WEIGHT.

(Repeat this procedure using an increment of 2, what does this do?)

13. Now, save your work by clicking on the option ‘Save Project As’ under ‘File’ and save it in

h:\minitab.

ASSIGNMENT

Practice what you have learned about MINITAB to accomplish the following.

There is interest in the difference (if any) between the effect the running exercises had on PULSE2 for men compared to women. Using MINITAB, draw dotplots of PULSE2 for the following groups:

Men who ran;

Men who didn't run;

Women who ran;

Women who didn't run;

Describe what you are seeing and discuss any differences.

Compute summary statistics for each of these groups. Record the following statistics:

Number in each group

Mean for each group

Median for each group

Inter-quartile range for each group.

Does there appear to be a gender difference between the groups ? Using some summary statistics and plots investigate one other variable (other than RAN and SEX) which may have an influence on pulse rate. What are your conclusions ?

Hint: To accomplish this create a new variable which categorises people in male - ran ; male - no run; female ran; female no run; groups. Use the 'manip / code / numeric to numeric' menu and some simple addition to accomplish this.

REVISION SUMMARY

After this lab you should be able to :

-  Generate histograms and understand the option ‘cutpoint’

-  Generate dotplots

-  Generate stem-and-leaf diagrams and understand the ‘increment’ option

-  Understand the use of the ‘by’ variable and be able to use it in the above graphs and when generating summary statistics

-  Unstack a variable using the ‘by’ variable function

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