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Budgets: determine the sample size as quickly as possible

Matthew S. Mayo, Ph.D.Director, Center for Biostatistics and Advanced InformaticsProfessor and Chair, Department of Biostatistics

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The Size of an Experiment

How many patients/animals do we need?Six key questions regarding the trial’s size:

1. What is the main purpose of the trial?2. What is the primary measure of outcome?

3. What is the experimental design and how will the data be analyzed to detect a treatment difference?

4. What type of results does one anticipate with standard treatment?

5. How small a treatment difference is it important to detect and with what degree of certainty?

6. How many patients/animals can you actually accrue per a given time frame?

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The BIG 4:

1. Type I error rate

2. Type II error rate = 1 – Power

3. Effect Size (difference one wishes to detect)

4. Sample Size

Note: Many times estimation of effect is more important, especially in early Phase I or II trials. Thus, Power is not an issue. Here one wants to estimate a measure of interest with a certain degree of precision.

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Other Issues

1. Length of follow-up

2. Are there more than two groups

3. Are there multiple sites

4. How many variables and data items are being collected

5. Building the database

6. Data quality and assurance

7. Does there need to be any interim analyses

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Finally

1. Contact us as soon as you start developing your idea

2. Need to be realistic about what can actually be done

3. A single study cannot answer every question

4. We are here to help – biostatistics.kumc.edu or 8-4703