# Probability

1. A Survey of 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.

Left handed= 6

Right handed = 24

Total Female lefty =4 righty=16

Male lefty Total= 2 righty=8

1. If a person is randomly selected from the survey participants, what is the probability that the person will be left-handed?
2. If you randomly choose a female from the people you surveyed, what is the probability that she is left-handed?
3. What is the odds ratio of choosing a left-handed female?
4. 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)

1. Probability of Green – (A+C)/(A+B+C+D): 70/130 = 0.54
2. Probability of Green Cat – A/(A+B): 40/60 = 0.67
3. Odds Ratio of Green Cat – (A/B)/(C/D) or AD/BC: (4040)/(2030) = 1600/600 = 2.67
4. Relative Risk of Green Cat – [A/(A+C)]/[B/(B+D)]: (40/70)/(20/60) = 1.71
5. Skim through at least one of the following articles on left-handed vs. right-handed people from the Chamberlain Library. Answer the following question: How do the probabilities and percentages for your study compare to those in the study you read?