Some Useful Statistics Definitions

The Four Fundamental Numbers

In Tabular Form

For individuals tested for some condition, disease, or other attribute:

Doesn't Have The Condition
(Satisfies Null Hypothesis)
Has The Condition
(Does Not Satisfy Null Hypothesis)
Tests Negative
(Null Accepted)
True Negative
TN or n00
False Negative
FN or n10
Tests Positive
(Null Rejected)
False Positive
FP or n01
True Positive
TP or n11

In Words

The Four (or Eight) Basic Ratios

Each of these four fundamental numbers can be divided by its row sum or its column sum.  This gives eight basic ratios, though they come in pairs that sum to one.

The Four Ratios of Ratios

Each specific test result (positive or negative) and each specific state (having the condition or not) can be used to define a ratio of ratios:

The Test As a Whole

Rather than focusing on what the data implies about any given tested individual, we can measure the quality of the test as a whole.  That is, for a specific distinctiveness criterion, and specific assumptions about the two groups we are testing (individuals who satisfy null hypothesis vs. those who do not), we can ask what is the chance that the distinctiveness criterion will be satisfied.

Copyright 2005, 2006, Lee Newberg.  All rights reserved.