Psychology Statistics (Chapter 6)

Probability

When several outcomes are possible, this is the likelihood of any particular outcome expressed in terms of a fraction or proportion

Formula for probability of A

Number of outcomes classified as A/divided by the total number of outcomes.

Requirements for random sampling

Every individual in the population has an equal chance of being selected

When more than one individual is being selected, the probabilities must stay constant. This means there must be sampling with replacement.

Step 1 of probablity question

restate the question in probability notation

Step 2 of probablity question

translate into a proportion question

Step 3 of probablity question

determine on the normal distribution what we are interested in finding

Step 4 of probability question

identify the exact position of X by computing a z-score

Step 5 of probability question

express our proportion in terms of a z-score

Percentage of 1 standard deviation away from the mean for a normal distribution

34.13% of the data falls within this range on a normal distribution.

Percentage of 2 standard deviation away from the mean for a normal distribution

13.59% of the data falls within this range on a normal distribution

Percentage of 3 standard deviation away from the mean for a normal distribution

2.28% of the data falls within this range on a normal distribution