Chapter 12: Power and Power calculations

Question 1

Alpha limits the probability of making a ___ error which means?

Answer 1

• type 1

- rejecting Ho and when it is true

Question 2

Fill in the state of reality table with the correct formulas:
State of reality
Decision: Ho true | Ho false
Retain Ho| Correct D | Type 2 error

Reject Ho| Type 1 error | Correct D

Answer 2

A) 1- alpha
B) Beta (B)
C) alpha value
D) 1- Beta (B)

Question 3

What does Beta limit the probability of ? What does that mean?

Answer 3

• limits the probability of making a type 2 error, retaining Ho when it is false.

Question 4

What is power?(3)

Answer 4

• sensitivity of an experiment to detect a real effect of the IV if there is one.
• Probability that results of an experiment will allow the rejection of Ho if IV has a real effect
• Probability that results of exp will allow rejection of Ho if Ho is false.

Question 5

What is powers range?

Answer 5

• 0.00 to 1.00

Question 6

Is a power of 0.80 common in behavioural sciences?

What about 0.40-0.60 range?

Answer 6

• NO

- common

Question 7

What are two things one must consider before an experiment?

Answer 7

• power analysis

- based on previous research

Question 8

So in laymen terms what does power do?

Answer 8

• calc the prob of detecting a real effect/difference

Question 9

Power varies directly with ___ and ___ but inversely with ____. (explain the blanks as well)

Answer 9

• Sample Size: more N= more power
• Large effect= more power
• alpha level- more stringent alpha = less power

Question 10

Small effect size vs large effect size?

Answer 10

• small: distance between is small

- = distance between is large

Question 11

Small sample size vs large sample size?

Answer 11

• small: increased variability, less precision(hard to tell the difference)
• large: decreased variability, more precision (easy to tell a difference)

Question 12

What is the formula for power?

Answer 12

1- B (beta)

Question 13

What are the two steps involved in computing power?

hint: sample outcomes, sample mean *

Answer 13

• Determine possible sample outcomes that would allow Ho to be rejected
• Determine probability of sample mean in critical region if hypothesized real effect of IV is true
• • Resulting probability = power

Question 14

In power questions you will be given what info? In step one calc.
What must you calc from it?

Answer 14

• N (sample size)
• Mean of null-hypothesis population ( Unull)
• Standard deviation of null population (you will have to calc the standard error)
• Alpha
• -> calc standard error and the Xcrit (rearrange z score formula to solve for it)
• • b/c you will know Zcrit from the apha

Question 15

Conclusion from calculating power???

Answer 15

If N= X, reject Ho if Xobt> Xcrit

Question 16

In step two you must calc the probability of a sample mean in the critical region for when the IV has a real effect. What is the formula for this?/step

Answer 16

• Zobt = Xobt-Ureal/ Ox

Power= zobt + 0.5000 or just Zobt (depends on where zobt lies on the distribution)

Question 17

You can also be asked to solve for N when you know the power. What is the formula for N?

Answer 17

N= [ o( Zcrit- Zobt)/(Ureal-Unull) ]^2