# Probability

look at probability in terms of both the real world and the medical community.

Survey 30 people to find out if they are left-handed or right-handed, and use the following chart to create a contingency table with the information.

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Left handed Right handed Total Female Male Total

If a person is randomly selected from the survey participants, what is the probability that the person will be left-handed?
If you randomly choose a female from the people you surveyed, what is the probability that she is left-handed?
What is the odds ratio of choosing a left-handed female?
What is the relative risk of choosing a left-handed female?

Example:

green                  blue                            total
cats                                                    40(A)                 20(B)                         60(A+B)

dogs                                                    30(C)                 40(D)                         70(C+D)

total                                                   70(A+C)            60(B+D)                 130(A+B+C+D)

Probability of Green – (A+C)/(A+B+C+D): 70/130 = 0.54
Probability of Green Cat – A/(A+B): 40/60 = 0.67
Odds Ratio of Green Cat – (A/B)/(C/D) or AD/BC: (4040)/(2030) = 1600/600 = 2.67
Relative Risk of Green Cat – [A/(A+C)]/[B/(B+D)]: (40/70)/(20/60) = 1.71

Answer the following question: How do the probabilities and percentages for your study compare to those in the study you read?

Read the below study as follows:

If you’re a lefty, you’re not alone.
Are you right-minded? If so, you are most likely one of the 10 percent to 13 percent of the world population that is lefthanded. Lefties are controlled by the right side of their brains, and so lefties are sometimes said to be the only people in their right minds!
Change-by Force
This wasn’t the story several decades ago. Left-handedness was considered by many to be a disorder-a problem that needed to be fixed. The Latin name for left-handed was “sinister,” and the connotations of the word seemed to bleed over to the people themselves.
Left-handed students were coerced, sometimes rather forcefully, to pick up a pencil with the other hand and “overcome” their preference. “This resulted in all kinds of problems from bed-wetting to stuttering,” says Dr. Sharlene McEvoy of Fairfield University in Connecticut, founder of The Sinistralian, a newsletter devoted to lefties. This practice has, in fact, strongly influenced some of the studies that are still being published today.
One of the biggest myths of left-handedness is that lefties die younger. But that just isn’t so.
“The study that stated that was based on faulty data,” says Dr. McEvoy. “The researcher studied the elderly and found few left-handers, so he surmised that it was because they had died. “However,” she continues, “it was actually due to the fact that most of the seniors weren’t allowed to be lefthanded as kids.”
Dr. Clare Porac, professor of psychology at Penn State Erie and researcher on lateral preference, agrees. “According to current research, many of the 80-year-olds interviewed were forced to change their hand preferences as children.” Fortunately, that has changed.
Myth vs. Reality
The line between what is fact and what is fiction about left-handedness is a thin one. What one researcher believes, another refutes. “The brain is too complex an organ for us to truly understand,” says Dr. McEvoy. “Research just isn’t that advanced.” Some studies, for instance, state that lefties are more prone to accidents and injuries at work because of having to deal with tools and other machines designed for right-handers. Dr. McEvoy says, “True. Left handers are more prone to injuries like carpal tunnel syndrome.”
Dr. Porac says, “No, there has been no higher incidence of work injuries in left-handers.” Some studies say lefthanders are more creative and intelligent. “Not true,” says Dr. Porac.
“Debatable,” says Dr. McEvoy. “For instance, lefthanders make up approximately 10 percent of the overall population, yet 20 percent to 25 percent of law students are left-handed-and so are 15 to 20 percent of the autistic population. What does that prove?”
What are the facts about being left-handed? “The fact,” says Dr. Porac, “is that lefthanders are pretty much just like right-handers. One of the only differences,” she continues, “is that left-handers are more variable in their hand use and brain organization. Righthanders are very strongly one sided, while left-handers are more flexible,” she continues. “In other words, left-handers can use their right hands better than right-handers can use their left hands.”
According to other research, lefties are also more prone to smoke cigarettes and drink alcohol. “This is due,” says Dr. McEvoy, “to the tensions of having to adapt to life in a right-handed world.” Both doctors agree that there are some definite links between left-handedness and autoimmune disorders such as asthma, diabetes, lupus, and multiple sclerosis. Why, however, remains a mystery to both.
Assessing the Cause
Just like the traits of lefties are up for debate, so is the original cause of left-handedness. Theories range from people having a left-handed gene to prenatal damage to birth defects, but the research doesn’t prove any of them. “We are simply born disposed one way or another,” says Dr. McEvoy. Genetics obviously plays a large role, though. Your chance of being lefthanded is one in 10 if both of your parents are right-handed, two in 10 if one parent is lefthanded, and three to four out of 10 if both parents are lefties.
Surprisingly, hand preference is not just limited to humans, either. According to Dr. McEvoy, most animals also show a preference in claw and paw. Even elephants have one tusk that they will present and use over another!
Being left-handed is certainly not the problem or disorder that it was once thought to be. In fact, if you decide to go to Juniata College in Huntingdon, Pennsylvania, it can even earn you a scholarship! The Mr. and Mrs. Frederick Beckley Scholarship was established by two student lefties who met and married at the college way back in 1924. In their wills, they set aside substantial money for any Juniata student who shows financial need, academic success-and writes with his or her left hand! +

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