chapter 5/6 Main ideas

Question 1

why are z scores useful

Answer 1

Using the mean and standard deviation to figure out the relative position of a particular score in a distribution. Useful when scores are on totally different scales because it puts them on the same scale. Also useful when variables have different means and SDs

Question 2

why standardize your scores?

Answer 2

1. ) to find a score’s position in a distribution. Can be used to find a percentile rank of a score.

2.) To compare scores of different distributions (put everything on the same scale). Apples and oranges can now be compared if converted to z scores.

3. it is the first step in computing correlations

Question 3

what is a z score

Answer 3

a score’s distance from the mean in standard deviation units.

it depends on the scores distance from the mean and the direction of the deviation, as well as the variability in the sample or population

Question 4

what is the z score range?

Answer 4

range from - 3.0 to 3.0.

Question 5

what does a z score of 0 mean

Answer 5

the score is at the mean

Question 6

what does a negative z score mean?

Answer 6

that a score is below the mean

Question 7

what does a positive z score mean?

Answer 7

a score is above the mean

Question 8

what does a z score of 1 mean?

Answer 8

it is one standard deviation above the mean

Question 9

What does a z score of -0.5 mean?

Answer 9

it is half a standard deviation below the mean

Question 10

what does a score of 2.8 mean?

Answer 10

it is 2.8 SD above the mean

Question 11

what is a z score distribution?

Answer 11

Covering all of the raw scores in a sample or population into z-scores and then plotting them in a frequency polygraph

Question 12

percentile rank

Answer 12

Each score can be converted into a percentile rank. If a score’s percentile rank is PR = 90, that means that 90% of the scores were lower than that

Question 13

percentile

Answer 13

the point in the distribution below which ___th percent of the scores fall, e.g., the 50th percentile (the median) is the score that below which 50% of all scores fal

Question 14

are there negative z scores?

Answer 14

There are no negative Z scores in the table; you have to remember that a negative z score means that a score is below the mean, and the percentile rank will always be < 50

Question 15

What does it mean when conclusions are based on statistical significance?

Answer 15

“unlikely to be due to chance variation.” or sampling error

Researchers are trying to sort out which differences are just sampling error and which differences are meaningful

Question 16

how do we make our decisions/inferences?

Answer 16

Never with certainty.

We use probability as the basis of our inferences.

Question 17

what is probability?

Answer 17

The likelihood that
an event will occur

Question 18

what is a complement?

Answer 18

the likelihood that an event wont occur