test. It measures the probability of the test correctly identifying a positive case of a disease (tnie-positive). Specificity is the proportion of person:; wilhoul a disease who have negative results on a screening lcsl. II n1cns11res the prr>hability of correctly identifying non-cases (true-negative) (Ander. son an<l Mcfo',irlane, :wn7). ·111e nurse must be aware of the sensitivity,incl spccificity rntes of screening measures that are used to detect a disease. In community situ:itions when there is ;m imm!!diat e need to as<.-crtain disease status, the nurse sel!!cts scrr:ening measures thal will yield I he highest probability of true-positive for the purpose of providing appropriate treatment and consequently prevent the transmission of cfo;. casc tot he rest of the healthy ropulation. On the othe. r lwncl, if resources are limitcd to the extent th:il scrcc!ning can not he done to all people suspected of the disem,c, the nursc will have to c Qrnpromi sc with screening tests with high specificity, identi(ying only those who "do not have the disease". TI1e choice of having a specific or a sensitive scrc.-enini. : test is not an easy one fnr the nuri,e. If she chooses one thal hns high sensitivity, there is Lhut probabil ity of some people having the disci1sc that will not be detected hy the screening test. This is referred to as false negative. 'J11is implics thrit these? reople may not be given ;ippropriate treatment having tested neg;itive rn the test. If the nurse decides on tests lhal have high specificity, there is probability that some people who do not actually have tl1e disease will be diagnosed !L'l "diseased"'. This is rcforrccl to as false positive. Peorle who arc false positives may be referred lo hospitals for trc,1Lmcnt when in fact, they are not ill. Table 7. 5 shows the rclnlion~hip of sensitivity a11d specificity of a screening test: TABLE 7. 5 SENSITIVITY AND SPECIFICITY OF A SCREENING TEST Screening Test Disease Status Results-Wlttiout Total With Disease . True Positive Positive True Positive False Posftfve +False Positive ' ' ' False Negative, Negative False Negative True Negative +True Negative ' Total Total Wlth Disease Total Without \ ' Disease. ' '. '.. True poslt1Ve5 Se'nsltll,:lty, or True-Positive Rate=------------Kl OO Total with disease ' ' True negatives Speclficit-y: or True,Ne~tive Rate. =---·-xl OO I; I ' ' Total without. clsease ' False negatives False-N'egatlve Rate =-------·---IC 100. ;. ' Total with disease I ' ' ' '.. False positives ' ' False-Positive Rare =-·--------------xl OO ' ' Total without disease ' ' '. ' Ma0c Mahon & Pugh, (1'9"70). Epidemldlogy: Pr/help/es and Methods. Boston, MA: Little, ', ' · Brown and Co. 193 