Chapter 17

Question 1

What is required to achieve valid and significant results?

Answer 1

An adequate number of study participants.

Question 2

How do you pick the correct number of study participants?

Answer 2

Based on statistical estimations about how many people are required to answer the study question with a specified level of certainty.

Question 3

What happens if too many participants are recruited?

Answer 3

Resources are wasted, including the time of both the researcher and the participants.

Question 4

What happens if too few participants are recruited?

Answer 4

The whole study will be worthless, because the sample will not have enough statistical power to answer the study question.

Question 5

Which population samples usually yield a sample mean close to the true population value?

Answer 5

Large samples

Question 6

What is a confidence interval?

Answer 6

An estimate of how close to the population value (like the mean) a sample of a particular size is expected to be.

Question 7

When the sample size is small, then it is represented by a _____(narrow/wide) confidence interval. When the sample size is large, that it is represented by a _____(narrow/wide) confidence interval.

Answer 7

Wide; narrow (greater certainty)

Question 8

What is the confidence interval calculated based on?

Answer 8

1) The number of individuals included in the sample
2) The mean age of those individuals
3) The standard deviation of their ages

Question 9

Larger sample size is make it more likely that a study will yield:

Answer 9

Statistically significant results

Question 10

What tool should be used early in the study design process to identify an appropriate goal for the number of participants will need to be recruited for the study?

Answer 10

A sample size calculator/Sample size estimator

Question 11

When the level of certainty about inputs is low, it is wise to:

Answer 11

Err on the side of a larger sample size.

Question 12

What is another way to check for sample size requirements?

Answer 12

To work backwards from the number of participants likely to be recruited to see whether a study population of that size will provide adequate statistical power for the study design.

Question 13

Power is related to the ability of a statistical test to do what?

Answer 13

Detect significant differences in a population when differences really do exist.

Question 14

What is a type one error?

Answer 14

A study population yields a significant statistical test result even though a significant difference or association does not actually exist in the source population. (Significant when NOT significant) (a=5%)

Question 15

What is a type two error?

Answer 15

A study population find no significant result even though there is a significant difference association in the source population (Not significant when IS significant) (B=20%)

Question 16

What is the formula for power?

Answer 16

1-B

If B=20%, Power=80%

Question 17

Both sample size estimates and power estimates require:

Answer 17

Best guesses about the expected findings of the study.

Question 18

If the power is less than 80% what can we do to improve it?

Answer 18

Increase the sample size.

Question 19

What is the difference between the study population and the sample population?

Answer 19

Study population: The actual number of participants

Sample population: The number of individuals invited to participate in the study

Question 20

Sample size estimates refer to which population?

Answer 20

The study population

Question 21

If the researcher needs more participants than he can get, what should be done?

Answer 21

The study question, study approach, and/or the target and source population must be modified. A new plan must be crafted that is suitable for the sample that the researcher can get.