Survey Results

Practice

• The Neuroticism Measure

= 23.32

S = 6.24

n = 54

How many people likely have a neuroticism score between 29 and 34?

Practice

• (29-23.32) /6.24 = .91

• B = .3186

• ( 34-23.32)/6.26 = 1.71

• B =.4564

• .4564-.3186 = .1378

• .1378*54 = 7.44 or 7 people

Finding a score when given a probability

• What IQ score is required to fall in the top 20 percent of the population?

Step 1: Sketch out question

100 ?

.20

Step 2: Look in Table C

100 ?

.20

In column C get as close to .20 as you can and find the corresponding Z score = .84

Step 3: Find the X score that goes with the Z score

• Z score = .84• Z = (X - ) / • .84 = (X - 100) / 15

• Must solve for X• X = + (z)()• X = 100 + (.84)(15)

Step 3: Find the X score that goes with the Z score

• Z score = .84

• Z = (X - ) / • .84 = (X - 100) / 15

• Must solve for X

• X = + (z)()

• X = 100 + (.84)(15) = 112.6

• A score of 112.6 is needed to be in the top 20 percent!

Finding a score when given a probability

• What IQ score is required to fall in the bottom 10 percent of the population?

Step 1: Sketch out question

100

.10

Step 2: Look in Table C

100

In column C get as close to .10 as you can and find the corresponding Z score = - 1.28 (NOTICE-NEGATIVE)

.10

Step 3: Find the X score that goes with the Z score

• Must solve for X

• X = + (z)()

• 80.8 = 100 + (-1.28)(15)

Step 3: Find the X score that goes with the Z score

• Must solve for X

• X = + (z)()

• 80.8 = 100 + (-1.28)(15)

• Thus, a you need an IQ of 80.8 to fall in the bottom 10 percent of the population

Practice

• On the next test I will give an A to the top 5 percent of this class.

• The average test grade is 56.82 with a SD of 6.98.

• How many points on the test did you need to get to get an A?

Step 1: Sketch out question

.05

Step 2: Look in Table C

.05

In column C get as close to .05 as you can and find the corresponding Z score = 1.64

Step 3: Find the X score that goes with the Z score

• Must solve for X

• X = + (z)()

• 68.26 = 56.82 + (1.64)(6.98)

Step 3: Find the X score that goes with the Z score

• Must solve for X• X = + (z)()• 68.26 = 56.82 + (1.64)(6.98)

• Thus, a you need a score of 68.26 to get an A

Practice

• The prestigious Whatsamatta U will only take people scoring in the top 97% on the verbal section SAT (i.e., they reject the bottom 3%).

• What is the lowest score you can get on the SAT and still get accepted?

• Mean = 500; SD = 100

Step 1: Sketch out question

.03

Step 2: Look in Table CIn column C get as close to .03 as you can and find the corresponding Z score = -1.88

.03

Step 3: Find the X score that goes with the Z score

• Must solve for X

• X = + (z)()

• 312 = 500 + (-1.88)(100)

Step 3: Find the X score that goes with the Z score

• Must solve for X• X = + (z)()• 312 = 500 + (-1.88)(100)

• Thus, you need a score of 312 on the verbal SAT to get into this school

Practice

• IQ Tests – Mean = 100– SD = 15

– 7.11– 7.12

• 7.11Z = -2.0

p = .0228

• 7.12(.0228)(4000) = 91.2 students

Practice

• IQ Tests – Mean = 100– SD = 15

– 7.15– 7.16

• 7.15p =.02; Z = 2.06100 + (2.06)(15) = 130.9

• 7.16a) p = .05; Z = 1.65 (1.64 is fine too)64.3 + (1.65)(2.5) = 68.4 inches

b) (58 – 64.3)/2.5 = -2.52p = .0059

Practice

• Page 136– 7.19– 7.21

• 7.19a) Z = (30-35)/6 = -.83; p = .2967 Z = (40-35)/6 = .84; p =.2967

p = .2967 + .2967 = .5934 b) .5934

• 7.21Z = (20-35)/6 = -2.50; p = .4938Z = (30-35)/6 = -.83; p =.2967p = .4938 - .2067 = .1971

Practice

• 6.22

Practice

• X = Stanford-Binet• Y = WAIS• b = .80 (15 / 16) = .75• a = 100 – (.75)100 = 25

• Y = 25 + (.75)X• 73.75 = 25 + (.75)65

• It’s a bad idea to use the same cut off score for these two tests

Practice

• 6.5

Practice

• Page 96 # 5.5

• r = .51

Practice

• 7.27

• 7.29