Chapter 14: Independent Group t-Test

Question 1

When do you go by correlated group design?

Answer 1

• Null- hypothesis population u and o are unknown

- differences between PAIRED scores are analyzed.

Question 2

Experiment with two conditions?

Answer 2

• random sampling of subjects from population.

Question 3

What are the characteristics of Independent groups design?

• ____ of subjects from population
• _____ assignment to each condition
• Each subject is tested how many times?
• What are analyzed?
• t-test analyzes what?

Answer 3

• Random sampling of subjects from population
• Random assignment to each condition
• No basis for pairing of scores
• Each subject is tested ONLY once
• Raw scores are analyzed
• t-test analyzes difference between sample means.

Question 4

What are the alternative hypotheses for Directional and Nondirectional?

Answer 4

• U1 > U2 or U1

Question 5

What are the null hypotheses for Directional and Nondirectional?

Answer 5

• U1 <= U2 ( directional )

- U1 = U2 (nondirectional)

Question 6

Sample scores from condition 1 include:?

Answer 6

• U1= mean of pop that receives condition 1

- O1 = standard deviation of the pop that receives condition 1.

Question 7

Sample scores from condition 2 include:?

Answer 7

• U2= mean of pop that receives condition 2

- O2= standard deviation of the pop that receives condition 2

Question 8

What is the major assumption of independent groups design?(3)

Answer 8

• changing level of IV affects MEAN ONLY
• Does not affect standard deviation or variance
  Therefore: O^2 1 = O^2 1
• If IV has a real effect the means will differ, not variance
  L> IV assumed to equally affect each individual

Question 9

Sampling distribution of the difference between sample means ( X1-X2):

• Draw all possible samples of __ and ___, from a population of __ and __, and standard deviation of __ and __.
• Calculate __ and __ for each sample
• Calculate __-__ for all possible pairings of samples of size __ and __.

Answer 9

• n1, n2, u1, u2, o1, o2
• Xbar 1, Xbar 2
• Xbar 1- Xbar 2
• n1 and n2

Question 10

What is the formula for t-test of independent groups?

Answer 10

• Tobt = (X1-X2) - uX1- uX2/ square root of: S^2w( 1/n1 + 1/n2)
• ## S^2w = weighted estimate of o^2 (variance)

Question 11

What is the computational equation for tobt???

Answer 11

• tobt= (X1-X2)/ square root: (SS1+SS2/n1+n2-2) times by (1/n1+1/n2)

Question 12

What is the formula for df for independent groups?

Answer 12

• N-2

Question 13

Conclusion for independent groups? (t)

Answer 13

• | tobt | >= | tcrit |, reject Ho

Question 14

What is the formula for Tobt when n1=n2 ?

degrees of freedom ?

Answer 14

• Tobt= (X1-X2)/ square root of: SS1+SS2/ n(n-1)

- Df= N-2 (N= population NOT SAMPLE)

Question 15

What is the assumption of independent group t-tests?

Answer 15

• test is robust

Question 16

The sampling distribution is ___ distributed. If __=__ and >=.

Answer 16

• normally
• n1=n2
• n>= 30

Question 17

Homogeneity of variance? huh?

Answer 17

• O1^2 = O2^2

L> Mann- Whitney U

Question 18

What is the formula for effect size of independent groups?

Answer 18

• D= | X1- X2| / square root of: S2w

ala –> S2w= SS1+ SS2/ n1+n2-2

Question 19

What increases power??

Answer 19

• Great effect of IV
• Larger sample size
• Decreased variability

Question 20

Correlated t-tests is more powerful when correlation between paired scores is __.

Answer 20

• high

Question 21

What is the equation for confidence intervals?

• 95%
• 99%

Answer 21

• u lower= (X1-X2)- Sx1-x2 t0.025
• u upper= (X1-X2) + Sx1 - X2 t 0.025
• u lower= (X1-X2)- Sx1-X2 t 0.005
• u upper= (X1-X2) + SX1- X2 T 0.005

Question 22

SX1-X2=??

Answer 22

SQUARE ROOT OF: SS1+SS2/n1+n2-2)(1/n+1/n2)

Question 23

When interpreting confidence intervals the probability value applies to the __ not the ___.

Answer 23

• interval

- population mean