Specific sources of inaccuracy Pre- and post-test probability

-



1 specific sources of inaccuracy

1.1 interference test
1.2 overlap of tests
1.3 methods overcome inaccuracy





specific sources of inaccuracy

specific sources of inaccuracy when using likelihood ratio determine post-test probability include interference determinants or previous tests or overlap of test targets, explained below:


interference test

post-test probability, estimated pre-test probability likelihood ratio, should handled caution in individuals other determinants (such risk factors) general population, in individuals have undergone previous tests, because such determinants or tests may influence test in unpredictive ways, still causing inaccurate results. example risk factor of obesity additional abdominal fat can make difficult palpate abdominal organs , decrease resolution of abdominal ultrasonography, , similarly, remnant barium contrast previous radiography can interfere subsequent abdominal examinations, in effect decreasing sensitivities , specificities of such subsequent tests. on other hand, effect of interference can potentially improve efficacy of subsequent tests compared usage in reference group, such abdominal examinations being easier when performed on underweight people.


overlap of tests

furthermore, validity of calculations upon pre-test probability derived previous test depend on 2 tests not overlap in regard target parameter being tested, such blood tests of substances belonging 1 , same deranged metabolic pathway. example of extreme of such overlap sensitivity , specificity has been established blood test detecting substance x , , likewise 1 detecting substance y . if, in fact, substance x , substance y 1 , same substance, then, making 2 consecutive tests of 1 , same substance may not have diagnostic value @ all, although calculation appears show difference. in contrast interference described above, increasing overlap of tests decreases efficacy. in medical setting, diagnostic validity increased combining tests of different modalities avoid substantial overlap, example in making combination of blood test, biopsy , radiograph.


methods overcome inaccuracy

to avoid such sources of inaccuracy using likelihood ratios, optimal method gather large reference group of equivalent individuals, in order establish separate predictive values use of test in such individuals. however, more knowledge of individual s medical history, physical examination , previous test etc. individual becomes more differentiated, increasing difficulty find reference group establish tailored predictive values, making estimation of post-test probability predictive values invalid.


another method overcome such inaccuracies evaluating test result in context of diagnostic criteria, described in next section.








Comments

Post a Comment

Popular posts from this blog

Life and work Ustad Mansur

-
tulip kashmir (c. 1610) mansur naqqash the year of mansur s birth unknown. name suffixed in miniatures naqqash, can refer artist, painter, or carver, indicating came family in artistic profession. single miniature showing babur meeting sister (folio 8, national museum) attributed mansur otherwise finds no mention in babur s memoirs (baburnama). associated other artists of period including basawan, miskina , nanha. during akbar s reign appears have been involved colourist in plates book of akbar (akbarnama) , name not mentioned abu l-fazl among list of artists. akbar followed principle artwork should include name of artist on margin. british museum s copy of akbarnama (1604) includes folios (35,110a,110b , 112a) name prefixed ustad (=master), indicating rise excellence. early works included parts of portraits , other scenes. earliest works made part of baburnama (1590–95) , of these assistant or colourist. veena-player (c. 1595) , coronation portrait of jahangir (c. 1605, made along
Read more

Examples Wreath product

-
^ j. w. davies , a. o. morris, schur multiplier of generalized symmetric group , j. london math. soc (2), 8, (1974), pp. 615-620 ^ p. graczyk, g. letac , h. massam, hyperoctahedral group, symmetric group representations , moments of real wishart distribution , j. theoret. probab. 18 (2005), no. 1, 1-42. ^ joseph j. rotman, introduction theory of groups, p. 176 (1995) ^ l. kaloujnine, la structure des p-groupes de sylow des groupes symétriques finis , annales scientifiques de l École normale supérieure. troisième série 65, pp. 239–276 (1948)
Read more

Kiev 35 mm cameras Kiev (brand)

-
kiev 4a rangefinder camera kiev 4 jupiter-8m lens , original camera case kiev produced several 35 mm film rangefinder cameras clones of pre-war contax ii , contax iii cameras, , range of 35mm slr cameras. after war had ended, soviet union demanded new sets of contax tools original toolmaker in dresden , ordered fair number of trial cameras made zeiss trademarks , coated lenses these 1946 in postwar east germany. successful, german instructors transferred kiev. missing specialists in few cases recruited in west germany. still available parts went in same direction. in fact, removing front of kiev ii cameras, 1 see metal stamped contax name, pressed out , re-stamped kiev. kiev 15 tee kiev 19 body kiev rangefinders retained same lens mount prewar contax rangefinders , lenses can interchanged. cameras went through few minor modifications become kiev iii , kiev 4. there kiev 5 modernized upper part integrated meter. attractive, though poorly made , unreliable, production terminated. other m
Read more