Understanding sensitivity and specificity with the right side of the brain

doi:10.1136/bmj.327.7417.716

BMJ 2003;327:716-719 (27 September), doi:10.1136/bmj.327.7417.716

Clinical review

Understanding sensitivity and specificity with the right side of the brain

Tze-Wey Loong, clinical teacher (part time)¹

¹ Department of Community, Occupational, and Family Medicine, National University of Singapore, Singapore

Correspondence to: T-W Loong, King George's Medical Centre, Block 803 King George's Avenue, #01-144, Singapore 200803, Singapore tzewey@singnet.com.sg

Can you explain why a test with 95% sensitivity might identifyonly 1% of affected people in the general population? The visualapproach in this article should make the reason clearer

The first 150 words of the full text of this article appear below.

Introduction

I first encountered sensitivity and specificity in medical school.That is, I remember my eyes glazing over on being told that"sensitivity = TP/TP+FN, where TP is the number of true positivesand FN is the number of false negatives." As a doctor I continuedto encounter sensitivity and specificity, and my bewildermentturned to frustration—these seemed such basic concepts;why were they so hard to grasp? Perhaps the left (logical) sideof my brain was not up to the task of comprehending these ideasand needed some help from the right (visual) side. What followsare diagrams that were useful to me in attempting to bettervisualise sensitivity, specificity, and their cousins positivepredictive value and negative predictive value.

Sensitivity and specificity

I will be using four symbols in these diagrams (fig 1). Letus start by looking at a hypothetical population (fig 2). Thesize of the . . . [Full text of this article]

Predictive values

A real example

Using both sides of the brain

CiteULike

Complore

Connotea

Del.icio.us Add to Digg

Digg

StumbleUpon Add to Technorati

Technorati What's this?

Relevant Articles

Do you ever mix up sensitivity and specificity?
BMJ 2003 327: 0. [Full Text]

Communicating risk: the main work of doctors: Richard Smith
BMJ 2003 327: 0. [Extract] [Full Text] [PDF]

This article has been cited by other articles:

Trikalinos, T. A., Siebert, U., Lau, J. (2009). Decision-Analytic Modeling to Evaluate Benefits and Harms of Medical Tests: Uses and Limitations. Med Decis Making 29: E22-E29 [Abstract]
Scott, V., Votova, K., Scanlan, A., Close, J. (2007). Multifactorial and functional mobility assessment tools for fall risk among older adults in community, home-support, long-term and acute care settings. Age Ageing 36: 130-139 [Abstract] [Full text]
Grabe, D. W, Cerulli, J., Stroup, J. S, Kane, M. P (2006). Comparison of the Achilles Express Ultrasonometer with Central Dual-Energy X-Ray Absorptiometry. The Annals of Pharmacotherapy 40: 830-835 [Abstract] [Full text]
Vanagas, G. (2004). Receiver operating characteristic curves and comparison of cardiac surgery risk stratification systems. ICVTS 3: 319-322 [Abstract] [Full text]
(2003). Hit Parade. BMJ 327: 1234-1234 [Full text]
Peile, E. (2003). learning to stay vigilant about conditions that are rare but important. BMJ 327: 919-919 [Full text]

Rapid Responses:

Read all Rapid Responses

It really can be confusing...: Graham B Byrnes
bmj.com, 26 Sep 2003 [Full text]
Best ever explanation of sensitivity and specificity: Nita G Forouhi
bmj.com, 26 Sep 2003 [Full text]
The question confuses rather than clarifies: Matthew McKenna
bmj.com, 26 Sep 2003 [Full text]
But it's got to get to the brain!: GH Hall
bmj.com, 26 Sep 2003 [Full text]
Confusing sensitivity for PPV: Antony R Goldstone, et al.
bmj.com, 26 Sep 2003 [Full text]
Don't confuse us further!: Angus Dobbie
bmj.com, 26 Sep 2003 [Full text]
Error in Calculations in Real Example: Susanne Haga
bmj.com, 27 Sep 2003 [Full text]
Mistake (left) in the last figure: Salvo Fedele
bmj.com, 27 Sep 2003 [Full text]
Precise language is still required for an accurate understanding of sensitivity and specificity.: Andrea Glassberg
bmj.com, 27 Sep 2003 [Full text]
But don't forget likelihood ratio!: Zeno Bisoffi, et al.
bmj.com, 27 Sep 2003 [Full text]
An excellent educational resource.: James H MacCabe
bmj.com, 27 Sep 2003 [Full text]
Oh dear: David JR Hutchon
bmj.com, 27 Sep 2003 [Full text]
Accuracy only 99%: Robert W Baker
bmj.com, 28 Sep 2003 [Full text]
Oops: Christopher J Martin, et al.
bmj.com, 28 Sep 2003 [Full text]
The over-riding importance of sensitivity: Richard G Fiddan-Green
bmj.com, 29 Sep 2003 [Full text]
Summary of responses so far: Tze-Wey Loong
bmj.com, 29 Sep 2003 [Full text]
Variable sensitivity and specificity: Christopher J Martin
bmj.com, 29 Sep 2003 [Full text]
Does sensitivity and specificity is REALLY not change?: Pisut Katavetin
bmj.com, 29 Sep 2003 [Full text]
One in a thousand?: Jennifer S Mindell
bmj.com, 29 Sep 2003 [Full text]
The left side of the brain needs to know what the right is doing: Colin C Geddes
bmj.com, 29 Sep 2003 [Full text]
A different approach to right brain thinking: Thomas F. Heston
bmj.com, 30 Sep 2003 [Full text]
Re: The over-riding importance of sensitivity: Sam Lewis
bmj.com, 30 Sep 2003 [Full text]
Teaching all this to medical students: Louis B. Jacques
bmj.com, 30 Sep 2003 [Full text]
Misunderstanding sensitivity: Sidney B Rosalki, et al.
bmj.com, 30 Sep 2003 [Full text]
Yes I can! but I think you meant something different: Chris D Evans
bmj.com, 1 Oct 2003 [Full text]
Clinical relevance of sensitivity and specificity: Nicola Petrucci
bmj.com, 1 Oct 2003 [Full text]
confused: adrienne j j garner
bmj.com, 2 Oct 2003 [Full text]
Clinical practice: not only percentage: Giulio Nati
bmj.com, 2 Oct 2003 [Full text]
Re: Clinical relevance of sensitivity and specificity: Pisut Katavetin
bmj.com, 2 Oct 2003 [Full text]
Congratulations: Sanjeev Sharma
bmj.com, 2 Oct 2003 [Full text]
Still confused?: Edward M Sivills
bmj.com, 3 Oct 2003 [Full text]
Lies damned lies and sub-editors: Paul G McIntyre
bmj.com, 3 Oct 2003 [Full text]
Quality control: Adam Jacobs
bmj.com, 5 Oct 2003 [Full text]
The right side of the brain wins in Italy too: Romolo M Dorizzi
bmj.com, 7 Oct 2003 [Full text]
Understanding Sensitivity & Specificity: Paul A Reeve
bmj.com, 7 Oct 2003 [Full text]
Confusing a clear cut concept: EAA Addou
bmj.com, 7 Oct 2003 [Full text]
What is a bad test?: Arturo Knol
bmj.com, 10 Oct 2003 [Full text]
Its true! The weird P comes to the rescue!: Taqi F Hashmi
bmj.com, 8 Oct 2003 [Full text]
Summary II; getting philosophical: Tze-Wey Loong
bmj.com, 14 Oct 2003 [Full text]
The Right Brain myth.: Neil Watson, MA, MD, FRCS
bmj.com, 14 Oct 2003 [Full text]
further comments: Fiona J Day
bmj.com, 17 Oct 2003 [Full text]
SpPIN or SnNOUT the diagnosis: Kit Byatt
bmj.com, 24 Oct 2003 [Full text]
Re: SpPIN or SnNOUT the diagnosis: Ian P Rodd
bmj.com, 21 Jan 2004 [Full text]
Communicating about sensitivity and specificity: Ben D Ewald
bmj.com, 11 May 2004 [Full text]
Keep it simple for the students: Anthony M. Benis, Sc.D., M.D.
bmj.com, 22 Mar 2006 [Full text]
Thank you!: Roxsie A Degen
bmj.com, 5 Dec 2007 [Full text]