Quantitative Vs. Qualitative Data and Laboratory Testing PDF

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Quantitative Vs. Qualitative Data and Laboratory Testing...

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QUANTITATIVE VS. QUALITATIVE DATA AND LABORATORY TESTING

Quantitative Vs. Qualitative Data and Laboratory Testing •

Quantitative data is numerical data, whereas qualitative data has no numbers 1attached to it.

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The gender of respondents2 in a study, dividing light bulbs3 into categories like "very bright," "somewhat bright" and "dim," or the type of pizza a customer prefers are all examples of qualitative data.

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If you say, by contrast, that 51 % of the plants tested grew to 10 inches or more, while 33 % grew to 5 inches or less, you are looking at quantitative data.4 By definition is non-numerical, but can sometimes be assembled to provide quantitative data. •

if customers in a survey describe how they feel about a food item they purchased, the questionnaire would only provide qualitative data.

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If the individual questionnaire results were compiled to determine how many or what percentage of customers prefer pepperoni to anchovies, however, the survey would now have provided some quantitative data as well.

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Enzyme-linked immunosorbent assay (ELISA) can be performed using approaches that will provide either qualitative or quantitative results.

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Pregnancy test is qualitative; it tests for the presence of human chorionic gonadotrophin (HCG) in the patient's urine, but does not quantify the amount present.

Choosing the Correct test for the Desired result Qualitative Assays •

Help to identify the presence or absence of the analyte (pathogen, toxin, antigen, antibody) being tested and are often useful as initial screening tests.

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May be useful in monitoring disease or treatment progress.

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Typically reported as positive/negative, detected/not detected. •

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Detection limits are set by the laboratory and based on the analyte tested, 11confidence level (controls), and kit used in order to provide the optimum combination of sensitivity and specificity.

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Results of similar qualitative assays performed by the same methodology in different laboratories may have slight variations in sensitivity and specificity, but these variations should not be significant.

Laboratory Tests •

Some lab tests provide qualitative results and others quantitative.

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Western blot, for example, typically provides only qualitative data  whether or not a particular protein was present, but not how much of it was present.

In some cases, the result may be reported as equivocal, indicating a level of response that falls in a gray zone of neither positive nor negative.

Quantitative Assays

QUANTITATIVE VS. QUALITATIVE DATA AND LABORATORY TESTING

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May be used as an initial test or as a reflex test added after the analyte has been found present by a qualitative assay.

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Results provide information on the amount of the analyte in the sample relative to the reference materials established by the WHO or other standards.

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Each certified laboratory calibrates its quantitative assays to who reference materials.

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Quantitative results are reported numerically and are compared against an accompanying reference interval for interpretation.

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Titers are a variation of a semi-quantitative assay and report the relative amount of an analyte within the sample.

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The assay requires titration of the specimen into serial dilutions to detect the point at which the analyte is no longer detected.

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Dilution standards are set by the performing laboratory and can vary significantly between laboratories.

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Titers are usually reported as a ratio of the highest dilution that still allows detection of the analyte,

Numeric results of quantitative assays performed by similar methods are comparable from laboratory to laboratory.

Semi-Quantitative Assays •

Titer Assays

Are similar to qualitative assays in detecting the presence or absence of an analyte but then go on to provide a numeric representation of the amount of the analyte in the specimen that is relative to the normal/abnormal threshold.

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Semi-quantitative results are compared against an accompanying reference interval to provide a qualitative interpretation of the result.

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WHO reference materials generally do not exist for an analyte reported as a semi-quantitative result, and response ranges may vary significantly between laboratories.

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Semi-quantitative numeric results from different performing laboratories may not be comparable, though the qualitative interpretation of the results will be similar.

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1:320, or as the reciprocal of the dilution, which would be 320 in this example.

The method involves visual observation by a trained technologist, and therefore will be subjective with some variation from laboratory to laboratory.

Verification of Performance Specifications •

Verification process confirms that the instrument and/or test method performs as the manufacturer intended when utilized in your laboratory environment, with your personnel, for your patient population.

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Must verify accuracy, precision, reportable range, and reference ranges for quantitative tests (tests that give a numerical result).

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If the test is qualitative (a test that gives a negative or positive result), only verification of accuracy is applicable.

QUANTITATIVE VS. QUALITATIVE DATA AND LABORATORY TESTING

personnel participate in the testing when assessing performance specifications.

Accuracy: •

How close a test result is to the analyte’s true value

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Can be verified by testing samples with known values and comparing the results you obtain.

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Acceptable limits must be established to define how close the results need to be.

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Accuracy for qualitative tests, you must verify that the test correctly identifies the presence or absence of the analyte.

Precision: •

The degree to which repeated test results on the same sample agree.

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Samples should be repeated and results compared within the same run, run-to-run, and day to-day.

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You must verify that results are reproducible in your lab, even when different testing personnel perform the test.

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Precision could also be applicable to qualitative testing.

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You could obtain a sample known to be positive and test it multiple times.

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However if you do not obtain a positive result each time, it is the accuracy (ability to detect the analyte being measured) of the test that is in question, and the test may not be suitable for use in your clinical setting.

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Inconsistent results could also be the result of operator error, which emphasizes the need to have different

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This enables you to detect test performance problems as well as training problems, and serves as a means to assess personnel competency.

Reportable range: •

The lowest and highest results that can be accurately measured and all the values in between.

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The manufacturer has established a reportable range for the test, which you must verify by testing known samples with values at the low and high end of that stated range.

Reference range: •

The span of values for a particular test that represents the results you would expect to see in a healthy (normal) patient population.

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Reference ranges establish the normal values for the test and should reflect the medical decision limits for clinicians.

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May use the manufacturer’s suggested reference range.

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Gravimetric method

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Titer assay

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Bacterial quantification...