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### Basic Mathematical Operations for Use in Statistics

The four basic mathematical operations are addition, subtraction, multiplication, and division (ah, yes — the basics you learned in elementary school). Different symbols indicate these operations. [more…]

### Test for Significance with Hypothesis Testing

All the famous statistical significance tests (Student t, chi-square, ANOVA, and so on) work on the same general principle — they evaluate the size of apparent effect you see in your data against the size [more…]

### How to Define Analytical Populations for a Clinical Study

*Analytical populations* are precisely defined subsets of the enrolled subjects that are used for different kinds of statistical analysis. Most clinical trials include the following types of analytical populations [more…]

### How to Deal with Missing Data from a Clinical Trial

Most clinical trials have incomplete data for one or more variables, which can be a real headache when analyzing your data. The statistical aspects of missing data are quite complicated, so you should [more…]

### How to Handle Multiplicity in Clinical Trial Data

Every time you perform a statistical significance test, you run a chance of being fooled by random fluctuations into thinking that some real effect is present in your data when, in fact, none exists. [more…]

### How to Incorporate Interim Analyses of Clinical Trial Data

An *interim analysis* is one that's carried out before the conclusion of a clinical trial, using only the data that has been obtained so far. Interim analyses can be blinded or unblinded and can be done [more…]

### Not Ready for Human Consumption: Doing Preclinical Studies

Before any proposed treatment can be tested on humans, there must be at least *some* reason to believe that the treatment might work and that it won't put the subjects at undue risk. So every promising chemical [more…]

### Human Drug Testing Phase I: Determining the Maximum Tolerated Dose

The first step (Phase I) in human drug testing is to determine how much drug you can safely give to a person, which scientists express in more-precisely defined terms: [more…]

### Human Drug Testing Phase II: Finding Out About the Drug's Performance

After the Phase I trials of human drug testing, you'll have a good estimate of the maximum tolerated dose (MTD) for the drug. The next step is to find out about the drug's safety and efficacy at various [more…]

### Human Drug Testing Phase III: Proving That the Drug Works

If Phase II of human drug testing is successful, it means you've found one or two doses for which the drug appears to be safe and effective. Now you take those doses into the final stage of drug testing [more…]

### What Are Bioequivalence Studies?

A *bioequivalence study* is usually a fairly simple pharmacokinetic study, having either a parallel or a crossover design. You may be making a generic drug to compete with a brand-name drug already on the [more…]

### How to Create a Data Dictionary to Describe Your Biostatistics Data

Every research database, large or small, simple or complicated, should be accompanied by a *data dictionary* that describes the variables contained in the database. It will be invaluable if the person who [more…]

### How to Put Together a Protocol for a Clinical Study

A *protocol* is a document that lays out exactly what you plan to do in a clinical study. Ideally, every study involving human subjects should have a protocol. [more…]

### Protecting Clinical Study Subjects

After you've designed your study and have described it in the protocol document, it's time to set things in motion. In any research involving human subjects, two issues are of utmost importance: [more…]

### Collecting and Validating Clinical Study Data

If the case report form (CRF) has been carefully and logically designed, entering each subject's data in the right place on the CRF should be straightforward. Then you need to get this data into a computer [more…]

### Human Drug Testing Phase IV: Keeping an Eye on the Marketed Drug

Being able to market the drug doesn't mean you're out of the woods yet! During a drug's development, you've probably given the drug to hundreds or thousands of subjects, and no serious safety concerns [more…]

### Thorough QT (Interval) Studies in Biostatistics

In the mid-1900s it was recognized that certain drugs interfered with the ability of the heart to "recharge" its muscles between beats, which could lead to a particularly life-threatening form of cardiac [more…]

### Levels of Measurement for Biostatistics Data

Around the middle of the 20th century, the idea of *levels of measurement* caught the attention of biological and social-science researchers, and, in particular, psychologists. One classification scheme, [more…]

### How to Collect Categorical Data in Biostatistics

Setting up your data collection forms and database tables for categorical data requires more thought than you may expect. Everyone assumes he knows how to record and enter categorical data — you just type [more…]

### How to Record Numerical Data for Biostatistics

For numerical data, the main question is how much precision to record. Recording a numerical variable to as many decimal places as you have available is usually best. [more…]

### How to Enter Date and Time Data for Biostatistics

When you enter numerical data into your computer, *don**'**t* combine two numbers into a single variable (such as 145/85 for systolic and diastolic blood pressure). When it comes to dates and times, however, [more…]

### How to Summarize and Graph Categorical Data

A categorical variable is summarized in a fairly straightforward way. You just tally the number of subjects in each category and express this number as a count — and perhaps also as a percentage of the [more…]

### Other "Means" (besides the Arithmetic Mean) to Measure Central Tendency

Several other kinds of means, besides arithmetic, are useful measures of central tendency in certain circumstances. They're called *means* because they all involve the same [more…]

### Standard Deviation, Variance, and Coefficient of Variation of Biostatistics Data

The *standard deviation* (usually abbreviated *SD,**sd,* or just *s*) of a bunch of numbers tells you how much the individual numbers tend to differ (in either direction) from the mean. It's calculated as follows [more…]

### The Range of a Set of Numbers

The *range* of a set of values in your data is the difference between the smallest value (the *minimum* value) and the largest value (the *maximum* value):

Range [more…]