Biostatistics For Dummies

Chapter 11

Fuzzy In Equals Fuzzy Out: Pushing Imprecision through a Formula

In This Chapter

Checking out the general concept of error propagation

Propagating errors through simple mathematical expressions

Getting a grip on error propagation for more complicated expressions

In Chapters 9 and 10, I describe how you can estimate the precision of anything you can measure (like height and weight) or count (such as hospital admissions, adverse events, and responses to treatment). In this chapter, I show you how to estimate the precision of things you calculate from the things you measure or count (for example, you can calculate body mass index from height and weight measurements). I explain the concept of error propagation, and I describe some simple rules you can use for simple expressions, such as those involving only addition, subtraction, multiplication, and division. Then I show you how to deal with simple or complicated expressions without having to do any calculations at all, using readily available software to do all the hard work for you.

Knowing how to make these calculations is important because often you can’t directly measure the thing you’re really interested in; you have ...