Changes

==Selecting a cut-off for diagnostic tests==

==Selecting a cut-off for diagnostic tests==

Decisions made following diagnostic testing are usually dichotomous e.g. treat or do not treat the animal, therefore diagnostic tests are usually interpreted as dichotomous outcomes (diseased or non-diseased). In this case, if a diagnostic test is measuring a continuous outcome e.g. antibody titre then a cut-off for classifying animal’s as positive or negative must be selected.  

Decisions made following diagnostic testing are usually dichotomous e.g. treat or do not treat the animal, therefore diagnostic tests are usually interpreted as dichotomous outcomes (diseased or non-diseased). In this case, if a diagnostic test is measuring a continuous outcome e.g. antibody titre then a cut-off for classifying animal’s as positive or negative must be selected. At whichever point the cut-off is selected there is usually some overlap between results i.e. some diseased animals will have the same value as non-diseased animals and hence, there will be false-positive and false-negative results.

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| Therapeutic method

| Therapeutic method

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| An animal is classified as positive at the point where treatment would be administered

| Requires up to date knowledge of treatment methods

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| *Requires up to date knowledge of treatment methods

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| Predictive value method  

| Predictive value method  

| Currently the most common method of selecting a cut-off

| Currently the most common method of selecting a cut-off

| Scientific basis for selecting a cut-off

| *Scientific basis for selecting a cut-off

Takes charachteristics of the test into account

*Takes charachteristics of the test into account

Can be altered depending on objective of testing

*Can be altered depending on objective of testing

| Most complex method

| *Most complex method

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