Table 2.

Contingency Tables for Derivation of the Theoretical Sensitivity and Specificity of a Positive Florbetapir Amyloid Scan For the Presence of Neuropathologically Confirmed Alzheimer Disease Dementia

Majority Read	NP density moderate or frequent and Braak stage III-VI N = 618	NP density none or sparse and/or Braak stage 0-II N = 301
Florbetapir amyloid scan positive (N = 620)	a) N = 588	b) N = 32
Florbetapir amyloid scan negative (N = 299)	c) N = 30	d) N = 269
	Sensitivity = 95.1%	Specificity = 89.4%
Least Accurate Reader	NP density moderate or frequent Braak stage III-VI N = 618	NP density none or sparse Braak stage 0-II N = 301
Florbetapir amyloid scan positive N = 565	a) N = 427	b) N = 51
Florbetapir amyloid scan negative N = 354	c) N = 191	d) N = 250
	Sensitivity = 69.1%	Specificity = 83.0%

CERAD, Consortium to Establish a Registry for Alzheimer's Disease; NACC, National Alzheimer's Coordinating Center, University of Washington, Seattle, WA

The presence of neuropathologically confirmed Alzheimer disease dementia is defined as the presence of moderate or frequent CERAD cortical neuritic plaque (NP) density and Braak neurofibrillary stage III-VI. Two separate calculations are shown. One uses the results from the majority read of florbetapir scans; the other uses results from the least accurate of the 5 readers. Sensitivity is calculated as the ratio of a/(a + c); specificity is calculated as d/(b + d).