John C. Pezzullo

To estimate sample size in biostatistics, you must state the effect size of importance, or the effect size worth knowing about. If the true effect size is less than the “important” size, you don’t care if the test comes out nonsignificant. With a few shortcuts, you can pick an important effect size and find out how many participants you need, based on that effect size, for several common statistical tests.

As you dive deeper into the field of biostatistics, you'll need to develop a firm understanding of pharmacokinetics (PK) and pharmacodynamics (PD) and the differences between the two. The term pharmacokinetics (PK) refers to the study of How fast and how completely the drug is absorbed into the body (from the stomach and intestines if it's an oral drug) How the drug becomes distributed through the various body tissues and fluids, called body compartments (blood, muscle, fatty tissue, cerebrospinal fluid, and so on) To what extent (if any) the drug is metabolized (chemically modified) by enzymes produced in the liver and other organs How rapidly the drug is eliminated from the body (usually via urine, feces, and other routes) The term pharmacodynamics (PD) refers to the study of The relationship between the concentration of the drug in the body and the biological and physiological effects of the drug on the body or on other organisms (bacteria, parasites, and so forth) on or in the body.

Two quite different ideas about probability have coexisted for more than a century. These probability approaches, which differ in several important ways, are as follows: The frequentist view defines probability of some event in terms of the relative frequency with which the event tends to occur. The Bayesian view defines probability in more subjective terms — as a measure of the strength of your belief regarding the true situation.

The aims or goals of a study are short general statements (often just one statement) of the overall purpose of the trial. For example, the aim of a study may be "to assess the safety and efficacy of drug XYZ in patients with moderate hyperlipidemia." The objectives are much more specific than the aims. Objectives usually refer to the effect of the product on specific safety and efficacy variables, at specific points in time, in specific groups of subjects.

The theory of statistical hypothesis testing was developed in the early 20th century and has been the mainstay of practical statistics ever since. It was designed to apply the scientific method to situations involving data with random fluctuations (and almost all real-world data has random fluctuations). Following are a few terms commonly used in hypothesis testing.

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 created the database is no longer around. A data dictionary is, itself, a data file, containing one record for every variable in the database.

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: This formula is saying that you calculate the standard deviation of a set of N numbers (Xi) by subtracting the mean from each value to get the deviation (di) of each value from the mean, squaring each of these deviations, adding up the terms, dividing by N – 1, and then taking the square root.

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 market whose patent has expired. The generic and brand-name drug are the exact same chemical, so it may not seem reasonable to have to go through the entire drug development process for a generic drug.

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 doses. You may also be looking at several different dosing regimens, including the following options: What route (oral or intravenous, for example) to give the drug How frequently to give the drug For how long (or for what duration) to give the drug Generally, you have several Phase II studies, with each study testing the drug at several different dose levels up to the MTD to find the dose that offers the best tradeoff between safety and efficacy.