Week 4 Discussion: Probability

Greetings Class Members !!

For grading purposes, this particular discussion posting area runs from Sunday Jan 24 through Sunday Jan 31, inclusively.

We explore ( mathematical ) Probability this Week. This includes probability concepts, conditional probability, independence, dependence, event( s ), the concept of “mutually exclusive,” the concept of “complement,” the multiplication rule, and the addition rule.

Please don’t forget to use an “outside” resource as part of the content and documentation for your first Post – the Post which is due on or before Wednesday of the Week – the Post where you make the most major contribution to the Weekly discussion posting area and attempt to address the discussion prompts / cues for the Week. It could possibly include a web site that you discovered on the internet at large, so long as the web site is relevant and substantial and does not violate the Chamberlain University policy for prohibited web sites, and so forth. It could possibly include references / resources that you discover through making use of the online Chamberlain University Library ( please click Resources along the left and then click Library to discover the link to the Chamberlain University online Library ) .

Check out the link below for some information about concepts such as independence, dependence, mutually exclusive, disjoint, complement, and conditional probability.

Link (Links to an external site.)Links to an external site.

This is one kind of an example of using an “outside” source / resource to add to what is revealed in our Weekly Lesson in Modules and in our Weekly text book reading.

Please don’t forget to look over the Graded Discussion Posting Rubric each Week to be certain that you are meeting all of the Frequency requirements as well as all of the Quality requirements for graded discussion posting each Week.

If you have any questions about anything, please do not hesitate to post in the Q & A Forum discussion posting area or to send me a direct e-mail message to  CSmith10@chamberlain.edu

Thanks Friends and Good Luck !  Work hard and learn a lot !!

Hi Friends and Greetings !!

Please remember that probabilities are NOT percentages and so the answers ( no doubt approximate and rounded off ) in the examples about the green cat above should please be respectively

0.54      0.67      for the two probability questions and

the answer for the odds ratio question should be approximately  2.67  and

the answer for the relative risk question should be approximately  1.71

You will want to please be very careful how you set up the rows and columns of your two way table ( which is also called a contingency table ) if you are hoping to make a perfect analogy between how the questions were worked out for the green cat and how the questions would be worked out for your left handed females.

Would the analogy work best if you set up your own two way table like this ??

Left HandedRight HandedTotalFemalesMalesTotal

I am really asking ( this is not rhetorical ) because I am just glancing at this assignment for the first time this morning.     

Also your lower right cell here should be 30 .

And the sum of the four cells involving left handed females, right handed females, left handed males, and right handed males should be 30 as well.

That is, you survey 30 humans and each human is placed into one and only one of those 4 possible cells.

Then you compute and fill in column totals and row totals.

Then as you will see the Table Total or the Grand Total in the lower right will be 30 .

Once you set up your contingency table ( two way table ) correctly, answering the 4 questions will be a breeze.  But give probabilities with answers like  0.XXXX  please !!

DON’T state a percentage as an answer to a probability question.

Try hard to use one of the two provided links to find your “outside” reference / resource this Week 4 .

It would get boring though in a large class if EVERYONE did that.  So please do that if you can but if a few Folks choose to find some other “outside” reference / resource this Week ( about left handedness and right handedness issues and trends and data ) that would certainly add some variety and freshness to our Week 4 graded Posting area.

Finally, many of you might make mistakes this Week, even though you have the example provided about the Green Cat( s )

So if you correct each other’s mistakes in follow up Posts, please be polite and sensitive and diplomatic and professional and all that – and I will try hard to do that as well.  We are all Friends and fellow learners here.

Thanks Friends and here below are a couple Videos to watch if you are concerned that the one Green Cat( s ) example is not quite enough to make you feel confident and secure about all of this.

Thanks Friends and work hard this Week 4 !  Your commitment and energy and drive and motivation will be put to the test during this Week 4 !!!

Professor and Class,

In order to gather the following data, I asked fellow family members and friends what their dominant hand was. It resulted in the following table:


If a person is randomly selected from the survey participants, what is the probability that the person will be left-handed?

9/30 participants were left-handed.

Probability: 9/30= 0.30

If you randomly choose a female from the people you surveyed, what is the probability that she is left-handed?

19/30 participants were female. Of those who were female 4/19 were left-handed.

Probability: 4/19= 0.21

What is the odds ratio of choosing a left-handed female?

(4/5)/(15/6)= 0.32

What is the relative risk of choosing a left-handed female?

[4/(4+15)]/[5/(5+6)] = (4/19)/(5/11)

Relative Risk= 0.46

I skimmed through the first article linked in our discussion “Being a Lefty is All Right” according to Orr, 2001 10 to 13% of the world’s population is left-handed. I thought this was a fairly small percentage, but it is even smaller than in the sample I collected. This is not unexpectedly however, as the law of large numbers states “as our sample size increases the probability found in the sample size will be closer to the expected outcome” (Week 4 Lesson: Probability in Everyday Life, 2021). According to Mwaniki, 2018 10-12% of the world’s population is left-handed and of those who are left-handed, men are 23% more likely to be than women. The fact of men being more likely than women to be left-handed also held true in my sample study.

Brennaa Sullivan


Mwaniki, A., (2018). What Percentage of The World Population Are Left Handed? World Atlas. https://www.worldatlas.com/articles/what-percentage-of-the-world-population-are-left-handed.htmlLinks to an external site.

Orr, T., (2001). Being a lefty is all right! Current Health. 28(2):12-13.

Week 4 Lesson: Probability in Everyday Life. (2021). Chamberlain University. https://chamberlain.instructure.com/courses/75447/pages/week-4-lesson-probability-in-everyday-life?module_item_id=10306877


Hi Friends !!   

A Probability Unit involves Vocabulary and concepts that most of you are probably less familiar with than say for example some of the material and info that we studied and learned about in Weeks 1-3 of the course.

Some of the Vocabulary that we will encounter during Week 4 of the course includes sample space, event, Tree Diagram, Venn Diagram, mutually exclusive, disjoint, complement, complementary events, conditional probability, independence, dependence, probability, odds, and much more !!

Please see the slides just below for some more info on a few of these concepts.  Two of the slides below involve what are called Venn Diagrams.

Note that “mutually exclusive” and “disjoint” are synonyms – they mean exactly the same thing.

The union of an event and its complement is sometimes called the “universe.”

That reminds me that union and intersection are also important concepts in Week 4 .       

One basic thing to always keep in mind about probabilities is that probabilities are NOT percentages.

So you have to resist the temptation to ever refer to a probability as a percentage even though you might see that done all over the general internet at large, and even in Academic Textbooks, and even perhaps in our own online text book, and even perhaps in places in our course shell / template here.

Another thing to remember about a probability is that a probability is no smaller than 0 and no larger than 1 .

Another way of saying that is to say that probabilities are never negative and probabilities are never larger than 1 .

You will see some but not all of the things that I have written here reinforced on the slides just below.

Thanks Friends and Good Luck during Week 4 !!