Getting Ready To Estimate Sample Size

Question 1

Are ways of calculating sample sizes true to reality?

Answer 1

No, they only are an estimate.

Question 2

What is the purpose of calculating sample size?

Answer 2

It gives us a feel of the study. It often reveals that the research design is not feasible, or that different predictor or outcome variables are needed.

Question 3

Is a research hypothesis and research question the same?

Answer 3

No

Research hypothesis is more specific to the study.

Question 4

What makes a good hypothesis?

Answer 4

Must be based on a good research question.

Should be simple, specific, and stated in advance.

Question 5

Can hypothesis contain more than one predictor or outcome variable?

Answer 5

Yes

Question 6

What should a specific hypothesis not leave out?

Answer 6

Who the subjects will be, what the predictor and outcome variables will be, and how the test of statistical significance will be applied.

Question 7

What can lead to over interpreting the importance of the findings in a research study?

Answer 7

Hypotheses that are formulated after examination of the data

Question 8

Should alternative hypotheses be one-sided or two-sided?

Answer 8

Two-sided

Question 9

What do grant and manuscript reviewers expect, an one-sided or two-sided hypothesis?

Answer 9

Two-sided

Question 10

Does the research hypothesis need to have the same “sides” as an alternative hypothesis?

Answer 10

No

The research hypothesis can be one-sided but he alternative should always be two-sided.

Question 11

What type of statistical error is a false-positive?

Answer 11

Type 1 error

Question 12

What type of statistical error is a false-negative?

Answer 12

A type 2 error

Question 13

An investigator does not know the exact effect size of a study, so what must she do?

Answer 13

She must choose the size of the association she expects to find.

Question 14

What is effect size?

Answer 14

It is the association the researcher believes she will find in the study.

Question 15

When calculating effect size, what should the investigator do first?

Answer 15

She should first try finding data from the literature in related areas to make an informed guess.

Question 16

If there are no datum for calculating effect size what should a researcher do?

Answer 16

Perform a pilot study

Question 17

When more than one predictor or outcome, which hypothesis do we use to calculate sample size?

Answer 17

The effect size for the most important hypothesis

Question 18

What is one of the important aims of sample size planning?

Answer 18

To keep alpha and beta at acceptably low levels without making the study unnecessarily expensive or difficult

Question 19

What result is better to report if the test was not significant (P>.05) probably due to low sample size?

Answer 19

The results, although suggestive of an association, did not achieve statistical significance (P=.08)

Question 20

Do statisticians and epidemiologists still favor the P value/hypothesis testing to report precision of the study results?

Answer 20

No, they are now frequently using confidence intervals. Only for sample size planning for analytical studies do p values continue to be the standard.

Question 21

If there is no association between the predictor and the outcome and we reject the null hypothesis, which type of error have we committed?

Answer 21

A type 1 error

Question 22

If there is an association between the predictor and the outcome and we fail to reject the null hypothesis, which type of error have we committed?

Answer 22

A type 2 error

Question 23

What is alpha?

Answer 23

It is the level of statistical significance in a study.

Question 24

What is the probability of making a type 2 error called?

Answer 24

Beta

Question 25

Power can be calculated by:

Answer 25

1 - beta

Question 26

What is power?

Answer 26

The probability of rejecting the null hypothesis when it should be rejected.

Question 27

What is hypothesis generation?

Answer 27

Also called data mining, are unanticipated associations that appear during the collection and analysis of a study’s result.

Question 28

What are the advantages of formulating more than one hypothesis or related hypotheses when planning a study?

Answer 28

• It increases the efficiency of the study
• Discover more of the true associations that exists in the population
• The study is more definitive

Question 29

What if only one hypothesis turns out to be statistically significant?

Answer 29

The author must decide(and try to convince editors and readers) whether the significant results, the nonsignificant results, or both sets of results are true