Statistics in medicine

Transcription

1 Sttistis in meiine Workshop 1: Sreening n ignosti test evlution Septemer 22, :00 AM to 11:50 AM Hope 110 Ftm Shel, MD, MS, MPH, PhD Assistnt Professor Chroni Epiemiology Deprtment Yle Shool of Puli Helth Ftm.shel@yle.eu S L I D E 0 Reiness ssessment questions Q1: A new sreening test for Zik hs een evelope. Whih test prmeter est esries the ility of this test to orretly ientify those iniviuls with Zik isese? A. preitive vlue B. preitive vlue C. Speifiity D. Sensitivity S L I D E 1 1

2 Reiness ssessment questions Q2: A new sreening test for Zik hs een evelope. Whih test prmeter est esries the ility of this test to orretly ientify those iniviuls with Zik isese out of the group of iniviuls with positive sreening tests? A. preitive vlue B. preitive vlue C. Speifiity D. Sensitivity S L I D E 2 Reiness ssessment questions Q3: A new sreening test for Zik hs een evelope. Whih test prmeter est esries the reprouiility of test? A. Aury B. Reliility C. likelihoo rtio D. likelihoo rtio S L I D E 3 2

3 Reiness ssessment questions Q4: A new sreening test for Zik hs een evelope. Whih test prmeter est esries the rtio of the likelihoo of otining negtive test result in ptient with the isese, to this likelihoo in ptient who oes not hve the isese? A. Aury B. Reliility C. likelihoo rtio D. likelihoo rtio S L I D E 4 Reiness ssessment questions Q5: A new sreening test for Zik hs een evelope. Whih test prmeter est esries the proportion of true mong ll test? A. likelihoo rtio B. likelihoo rtio C. Aury D. Reliility S L I D E 5 3

4 Reiness ssessment questions Q6-Q9: A stuy ws onute to evlute myoril infrtion s onfirme y the riologist n s ignose se on eletro rio grm (ECG). Use the following tle 1 to nswer questions 6 through 9. Tle 1: Q6-Q9 ECG Physiin ignosis MI No MI S L I D E 6 Reiness ssessment questions Q6- The sensitivity of ECG test is whih of the following? A B C D Sensitivity = TP TP+FN = + =15/(15+35)=0.30 S L I D E 7 4

5 Reiness ssessment questions Q7-The ury of the ECG test is whih of the following? A. 0.3 B C D. 0.6 Aury = TP+TN TP+FP+FN+TN = =(15+30)/( )=0.45 S L I D E 8 Reiness ssessment questions Q8- The flse positive rte of ECG test is whih of the following? A B C D Flse positive rte = FP TN+FP = + =20/(20+30)=0.40 S L I D E 9 5

6 Reiness ssessment questions Q9- The proility tht ptient who i not hve MI will hve negtive ECG is whih of the following? A. 0.4 B C D. 0.6 Speifiity = TN = =30/(20+30)=0.60 TN+FP + S L I D E 10 Evluting ignosti/sreening proeures Asent (D-) TP: positive test result in person who hs the isese FP: positive test result in person who oes not hve the isese FN: negtive test result in person who hs the isese TN: negtive test result in person who oes not hve the isese S L I D E 11 6

7 Evluting ignosti/sreening proeures: Sensitivity Asent (D-) Use isese olumn for sensitivity lultion Sensitivity: the ility of the test/proeure to etet those who hve the isese The proility of eing teste positive given eing isese The proportion of the isese who re orretly lssifie positive y the test The proportion tht tests positive mong the isese Sensitivity = TP = TP+FN + S L I D E 12 Evluting ignosti/sreening proeures: Sensitivity Asent (D-) TP = TP+FN Sensitivity = + Sensitivity: with 100% sensitivity mens it will e positive for ny isese Zero flse negtive Sensitive test is importnt if flse negtive re serious ex. HIV test SNOUT: SeNsitive test with result rules OUT the isese Other rememering is: positivity in isese, sensitivity to isese S L I D E 13 7

8 Evluting ignosti/sreening proeures: Speifiity Asent (D-) Use unisese olumn for speifiity lultion Speifiity: the ility of the test/proeure to etet those who DO NOT hve the isese The proility of eing teste negtive given eing unisese The proportion of the unisese who re orretly lssifie negtive y the test S L I D E 14 Evluting ignosti/sreening proeures: Speifiity Asent (D-) Use unisese olumn for speifiity lultion Speifiity: The proportion tht tests negtive mong the unisese Speifiity = TN = TN+FP + S L I D E 15 8

9 Evluting ignosti/sreening proeures: Speifiity Asent (D-) TN = TN+FP Speifiity = Speifiity: + with 100% speifiity mens it will e negtive for ny unisese Zero flse positive Speifi test is importnt if flse positive re serious ex. Cner SPIN: SPeifi test with result rules IN the isese Other rememering is: negtive in helth, speifi to helth S L I D E 16 Evluting ignosti/sreening proeures: Reltionship etween sensitivity n speifiity Inversely relte i.e. inrese in one riteri use erese in the other riteri Beuse in rel life usully iniviuls with isese or without isese re on ontinuum i.e. not isrete groups The sensitivity n speifiity will epen on the utoff vlue of the test Reuing utoff vlue inrese sensitivity n erese speifiity, the opposite is true You n otin test with 100% sensitivity n 100% speifiity, ONLY, if there is no overlp in the test S L I D E 17 9

10 Use positive row for PPV lultion Use positive row for PPV lultion 11/3/2016 Evluting ignosti/sreening proeures: preitive vlue, 2 x 2 tle Asent (D-) PPV (PV+): How likely the isese is present The proility of eing isese given positive test The proportion of those who teste positive who hve the isese S L I D E 18 Evluting ignosti/sreening proeures: preitive vlue, 2 x 2 tle Asent (D-) PPV (PV+): How likely the isese is present PPV = TP = TP+FP + S L I D E 19 10

11 Use negtive row for NPV lultion Use negtive row for NPV lultion 11/3/2016 Evluting ignosti/sreening proeures: preitive vlue, 2 x 2 tle Asent (D-) NPV (PV-): How likely the isese is NOT present The proility of eing NOT isese given negtive test The proportion of those who teste negtive who DO NOT hve the isese S L I D E 20 Evluting ignosti/sreening proeures: preitive vlue, 2 x 2 tle Asent (D-) NPV (PV-): How likely the isese is NOT present NPV = TN = TN+N + S L I D E 21 11

12 Evluting ignosti/sreening proeures: Likelihoo rtios Likelihoo rtios: Are the rtios of the likelihoo tht the test ours in ptients with the isese versus the likelihoo tht the test ours in ptients without the isese Generl formul: Proility of test result in isese Proility of test result in unisese Two likelihoo rtios: Likelihoo rtio positive (LR+) Likelihoo rtio negtive(lr-) S L I D E 22 Evluting ignosti/sreening proeures: Likelihoo rtios Likelihoo rtio positive LR+: Is the likelihoo rtio of positive test Is the rtio of the likelihoo tht positive test ours in ptients with the isese versus the likelihoo tht positive test ours in ptients without the isese S L I D E 23 12

13 Evluting ignosti/sreening proeures: Likelihoo rtio positive LR+ Asent (D-) Likelihoo of mong isese = sensitivity Likelihoo of mong unisese = 1-speifiity LR+: How muh more likely o the ptient tully hs the isese given positive test? The rtio of true positive rte to the flse positive rte The higher the rtio the etter the test LR += TP/(TP+FN) FP/(FP+TN) =/(+) = sensitivity /(+) 1 speifiity S L I D E 24 Evluting ignosti/sreening proeures: Likelihoo rtios Likelihoo rtio negtive LR-: Is the likelihoo rtio of negtive test Is the rtio of the likelihoo tht negtive test ours in ptients with the isese versus the likelihoo tht negtive test ours in ptients without the isese S L I D E 25 13

14 Evluting ignosti/sreening proeures: Likelihoo rtio negtive LR- Asent (D-) Likelihoo of mong isese = 1-sensitivity Likelihoo of mong unisese = speifiity LR-: How muh less likely o the ptient tully hs the isese given negtive test? The rtio of flse negtive rte to the true negtive rte The lower the rtio the etter the test LR = FN/(TP+FN) = /(+) TN/(FP+TN) /(+) =1 sensitivity speifiity S L I D E 26 Evluting ignosti/sreening proeures: Reltionship etween sensitivity n speifiity Complete seprtion 100% speifiity, 100% sensitivity Threshol=200 D- D+ D- D Threshol= Threshol= % speifiity D- D+ D+ D S L I D E 27 14

15 A 100% sensitivity 0% flse negtive Inrese the flse-positive rte Derese the speifiity Inrese the negtive preitive vlue SNOUT: SeNsitive test with result rules OUT the isese Cutoff vlues 100% speifiity 0% flse positive Inrese the flse-negtive rte Derese the sensitivity Inrese the positive preitive vlue SPIN: SPeifi test with result rules IN the isese B resul ts (True positive TP) (Flse negtive FN) Asent (D-) (Flse positive FP) (True negtive TN) S L I D E 28 Applition Questions If X represents the most urte utoff point of ignosti test, use the figure elow to nswer questions 1-4. S L I D E 29 15

16 Applition Questions Q1- The utoff point for greter flse-positive rte is whih of the following? A. A B. X C. B D. None S L I D E 30 Applition Questions Q2- The utoff point for lesser sensitivity is whih of the following? A. A B. X C. B D. None S L I D E 31 16

17 Applition Questions Q1- The utoff point for greter flse-positive rte is whih of the following? Q2- The utoff point for lesser sensitivity is whih of the following? The hoie of utoff point ffets the test sensitivity, speifiity, flse positive rte, n flse negtive rte. The utoff point (X) is onsiere s the optiml utoff point sine it lnes the sensitivity n speifiity of the test. If we set the utoff point to lower vlue thn (X) suh s the (A) utoff point, then we inrese the sensitivity of the test, n hene we inrese the flse-positive rte n erese the speifiity, n inrese the negtive preitive vlue ue to the erese in the numer of flse negtive. On the other hn if we use higher vlue utoff point suh s (B), the test will etet fewer ses i.e. the sensitivity will erese, the flse positive numers will eline, flse negtive rte will inrese, n the speifiity of the isese will inrese, n the positive preitive vlue will inrese ue to the erese in the numer of flse positive. S L I D E 32 Applition Questions Q3- If sreening test hs ientifie numer of ptients with positive who potentilly hve ner. Whih of the letters in figure 1 represents the most pproprite eision limit for susequent onfirmtory test tht is to e performe on these ptients smples? A. A B. B C. X D. None S L I D E 33 17

18 Applition Questions Q3- If sreening test hs ientifie numer of ptients with positive who potentilly hve ner. Whih of the letters in figure 1 represents the most pproprite eision limit for susequent onfirmtory test tht is to e performe on these ptients smples? When pplying onfirmtory test, the intention is to use test tht woul hve no flse negtives, thus ll ptients who test positives y this onfirmtory test re true positives. As shown in the figure, t point B ll iniviuls who o not hve ner re elow the utoff point, euse point B is equl to speifiity of 100% (i.e. ll positives re true positives). In ontrst, if we re pplying n exlusion test, then point A is the utoff point in whih ll iniviuls with ners re ientifie euse point A is equl to sensitivity of 100% (i.e., ll negtives re true negtives). S L I D E 34 Applition Questions Q4- If the Amerin ssoition of ner reserh eie to lower the utoff vlue for ner ignosis from B to A. This hnge in utoff vlue most likely will le to A. Inrese the test s flse preitive rte B. Inrese the test s speifiity C. Derese the test s sensitivity D. Inrese the test negtive preitive vlue S L I D E 35 18

19 Applition Questions Q4- If the Amerin ssoition of ner reserh eie to lower the utoff vlue for ner ignosis from B to A. This hnge in utoff vlue most likely will le to The hoie of utoff point ffets the test sensitivity, speifiity, flse positive rte, n flse negtive rte. The utoff point (X) is onsiere s the optiml utoff point sine it lnes the sensitivity n speifiity of the test. If we set the utoff point to lower vlue thn (X) suh s the (A) utoff point, then we inrese the sensitivity of the test, n hene we inrese the flse-positive rte n erese the speifiity, n inrese the negtive preitive vlue ue to the erese in the numer of flse negtive. On the other hn if we use higher vlue utoff point suh s (B), the test will etet fewer ses i.e. the sensitivity will erese, the flse positive numers will eline, flse negtive rte will inrese, n the speifiity of the isese will inrese, n the positive preitive vlue will inrese ue to the erese in the numer of flse positive. S L I D E 36 19