Chapter 12: Power and Power calculations Flashcards Preview

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Flashcards in Chapter 12: Power and Power calculations Deck (17):

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

- type 1
- rejecting Ho and when it is true


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

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


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

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


What is power?(3)

- 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.


What is powers range?

- 0.00 to 1.00


Is a power of 0.80 common in behavioural sciences?
What about 0.40-0.60 range?

- NO
- common


What are two things one must consider before an experiment?

- power analysis
- based on previous research


So in laymen terms what does power do?

- calc the prob of detecting a real effect/difference


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

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


Small effect size vs large effect size?

- small: distance between is small
-= distance between is large


Small sample size vs large sample size?

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


What is the formula for power?

1- B (beta)


What are the two steps involved in computing power?
hint: sample outcomes, sample mean *

- 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


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

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


Conclusion from calculating power???

If N= X, reject Ho if Xobt> Xcrit


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

- Zobt = Xobt-Ureal/ Ox

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


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

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