Evaluation of diagnostic tests - Revision history

Gauche at 15:28, 3 May 2011

2011-05-03T15:28:40Z

2011-05-03T15:25:01Z

Introduction

2011-05-03T15:22:05Z

Sensitivity and specificity

2011-05-03T15:16:33Z

Sensitivity and specificity

2011-05-03T14:55:39Z

2011-05-03T14:13:37Z

Predictive values

2011-05-03T14:08:42Z

Interpretation of diagnostic tests

2011-05-03T14:05:31Z

Interpretation of diagnostic tests

2011-05-03T14:00:05Z

Sensitivity and specificity

2011-05-03T13:57:35Z

Interpretation of diagnostic tests

← Older revision		Revision as of 15:28, 3 May 2011
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	[[File:post-test probability.jpg]]		[[File:post-test probability.jpg]]
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		+	[[Category:Veterinary Epidemiology - General Concepts\|K]]

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 <br />
-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. The figure below shows that whereever 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 resulting in some false-positive and false-negative results.
+A diagnostic test is an objective method of deciding whether an animal has a disease, or not. 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. The figure below shows that whereever 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 resulting in some false-positive and false-negative results.
 [[File:Diagnostic test results.jpg]]

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 '''Sensitivity (''Se'')''' is the probability that a positive animal is correctly identified as positive and '''specificity (''Sp'')''' is the probability a negative animal is correctly identified as negative.
-[[File:sensitivity.jpg]]
+[[File:specificity.jpg]]
 ===Predictive values===

← Older revision		Revision as of 15:16, 3 May 2011
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	'''Sensitivity (''Se'')''' is the probability that a positive animal is correctly identified as positive and '''specificity (''Sp'')''' is the probability a negative animal is correctly identified as negative.		'''Sensitivity (''Se'')''' is the probability that a positive animal is correctly identified as positive and '''specificity (''Sp'')''' is the probability a negative animal is correctly identified as negative.

		+	[[File:sensitivity.jpg]]

	===Predictive values===		===Predictive values===

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 ==Interpretation of diagnostic tests==
-Several statistics can aid clincians in the interpretation of diagnostic tests these include '''sensitivity''' and '''specificity''', '''predictive values''', '''likelihood ratios''' and '''pre-''' and '''post-test probabilities'''. The following 2 x 2 table is often used by epidemiologists to calculate these statistics:
+Several statistics can aid clinicians in the interpretation of diagnostic tests these include '''sensitivity''' and '''specificity''', '''predictive values''', '''likelihood ratios''' and '''pre-''' and '''post-test probabilities'''. The following 2 x 2 table is often used by epidemiologists to calculate these statistics:
 [[File:table.jpg]]
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 '''Sensitivity (''Se'')''' is the probability that a positive animal is correctly identified as positive and '''specificity (''Sp'')''' is the probability a negative animal is correctly identified as negative.
 ===Predictive values===
 There are two types of predictive value; '''positive predictive value (PV+)''' is defined as the probability that an animal which tests positive actually has the disease and '''negative predictive value (PV-)''' is the probability and animal that tests negative does not have the disease. PV+ and PV- are calculated as follows:
 ===Likelihood ratio===

← Older revision		Revision as of 14:13, 3 May 2011
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	===Predictive values===		===Predictive values===
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		+	There are two types of predictive value; '''positive predictive value (PV+)''' is defined as the probability that an animal which tests positive actually has the disease and '''negative predictive value (PV-)''' is the probability and animal that tests negative does not have the disease. PV+ and PV- are calculated as follows:

	===Likelihood ratio===		===Likelihood ratio===

← Older revision		Revision as of 14:08, 3 May 2011
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	==Interpretation of diagnostic tests==		==Interpretation of diagnostic tests==
−	Several statistics can aid clincians in the interpretation of diagnostic tests these include '''sensitivity''' and '''specificity''', '''predictive values''', '''likelihood ratios''' and '''pre-''' and '''post-test probabilities'''.	+	Several statistics can aid clincians in the interpretation of diagnostic tests these include '''sensitivity''' and '''specificity''', '''predictive values''', '''likelihood ratios''' and '''pre-''' and '''post-test probabilities'''. The following 2 x 2 table is often used by epidemiologists to calculate these statistics:
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		+	[[File:table.jpg]]

← Older revision		Revision as of 14:00, 3 May 2011
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	===Sensitivity and specificity===		===Sensitivity and specificity===
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		+	'''Sensitivity (''Se'')''' is the probability that a positive animal is correctly identified as positive and '''specificity (''Sp'')''' is the probability a negative animal is correctly identified as negative.

	===Predictive values===		===Predictive values===