How to Learn Everything You Ever Wanted to Know About BiostatisticsDaniel W. ByrneDirector of Biostatistics and Study Design

General Clinical Research Center Vanderbilt University Medical Center1

The presenter has no financial interests in the products mentioned in this talk.

Objective of This Workshop

To provide a 1-hour overview of the

important practical information that aclinical investigator needs to know about biostatistics to be successful.2

I. You Will Need the Right Tools

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Install a powerful, yet easy to use, statistical software package on your computer.

I recommend SPSS for Windows.

Bring an 1180 for $80 to Karen Montefioriin 143 Hill Student Center (3-1630).

She will lend you the SPSS CD for the dayand you can install this software easily.4

SPSS is the 2nd most popular package. It is much easier to use than SAS and Stata.1 2 3 4 5 6 7 8 9 10 163 SAS 52 48 36 22 19 12 8 6 5 SPSS STATA Epi Info SUDAAN S-PLUS Statxact BMDP Statistica Statview

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Install additional software for statistical odds and ends

Instat by GraphPad graphpad.com

for summary data analysis - $100

True Epistat by Epistat Services true-epistat.com - $395

for random number table, etc.for confidence intervals - $35.95 with book Statistics with Confidence D. Altman6

CIA (Confidence Interval Analysis) bmj.com

Install a sample size program.

If you can afford to spend $400, buy nQuery Advisor statistical solutions - www.statsol.com If you can afford to spend $0, download PS from the Vanderbilt web site

http://www.mc.vanderbilt.edu/prevmed/ps/index.htm

Both packages are on the CRCs statistical workstation in room A-3101. VUMC7

II. You Will Need a Plan

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Use the scientific method to keep your project focused.

State the problem Formulate the null hypothesis Design the study Collect the data Interpret the data Draw conclusions

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State the Problem

Among patients hospitalized for a hip fracture who develop pneumonia during their stay in the hospital, the mortality rate is 2.3 times higher at non-trauma centers compared with trauma centers (48.7% vs. 21.1%, P=0.043.) It is not clear if, or how, those who will develop pneumonia could be identified on admission.

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Formulate the Null Hypothesis

Among patients hospitalized for treatment of a hip fracture, there are no factors known upon admission that are statistically different between those who develop pneumonia during their stay and those who do not.

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Why bother with a null hypothesis?

For the same reason that we assume that a person is innocent until proven guilty. The burden of responsibility is on the prosecutor to demonstrate enough evidence for members of a jury to be convinced of that the charges are true and to change their minds. Outcome after treatment with Drug A will not be significantly different from placebo.12

Design the StudyData on 933 patients with a hip fracture from a New York trauma registry will be analyzed. The 58 patients with pneumonia will be compared with the 875 without pneumonia.

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The Most Common Type of FlawStudy Design Interpretation of the findings Importance of the topic Presentation of the results0 0 5 10 15 20 25 4 4 20

Number of Responses14

Example of Recall Bias

A control group is asked, Two weeks ago from today, did you eat X for breakfast? Two weeks after their MI, patients are asked Did you eat X for breakfast on the day of your heart attack? You can prove any food causes an MI using this method (X=bacon, X=Flintstone vitamins, etc.)15

John Bailars Quote:Study design and bias are much more important than complex statistical methods. Devote more time to improving the study design, and minimizing and measuring bias. Become an expert at study design issues and biases in your area of research.16

What is the statistical power of the study?Power Beta Alpha Sample size Ratio of treated to control group Measure of outcome

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Sample Size Table

See Table 9-1 in the handout Sample Size Requirements for Each of Two Groups.

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Collect the Data

See the handouts for: I TEC Trauma Systems Study

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III. You Will Need Data Management Skills

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Enter your data with statistical analysis in mind.For small projects enter data into Microsoft Excel or directly into SPSS. For large projects, create a database with Microsoft Access. Keep variables names in the first row, with