# Quality Assurance and Statistics Flashcards

If both the gold standard and your test produce the same positive results, this is called a (A) True negative (B) True positive (C) False positive (D) False negative

(B) “True positive” is when the test you are using produces the same results as the gold standard.

The positive predictive value is used to gauge

(A) How accurate the test is

(B) How sensitive the test is

(C) Ability of predicting abnormal results

(D) Ability of predicting negative results

(C) The positive predictive value (PPV) is used to describe how well a test can predict a positive, or abnormal, result.

Using a standard Chi square matrix the equation D÷(D+C) is used for determining what statistic? (A) Accuracy (B) Sensitivity (C) Positive predictive value (D) Negative predictive value

(D) D÷(D + C) is the formula for negative predictive value (NPV), a statistic that predicts how well a test can find a negative, or normal, result. Notice all the parts of the equation are “negative.” C is false negatives and D is true negatives.

Using a standard Chi square matrix which of the following equations is used to determine specificity? (A) A ÷ (A + B) (B) D ÷ (D + C) (C) D ÷ (D + B) (D) (A + D) ÷ (A + B + C + D)

(C) The equation for specificity, the statistic that states how good a test is at finding disease, is D÷(D+B), where D is true negatives and B is false positives.

Which of the following indicates how well a test provides the correct results, regardless of whether the result is positive or negative? (A) Accuracy (B) Specificity (C) Sensitivity (D) Positive predictive value

(A) Accuracy is how well a test provides the correct result, regardless of whether that result is positive or negative. Accuracy involves all the variables: true positives (A) + true negatives (D) divided by the sum of all the variables (A + B + C + D).

What is the purpose of testing and calibrating the pressure machine on a scheduled basis?

(A) To ensure the examination is being performed properly

(B) The hospital’s legal department requires it

(C) To ensure the machine is performing as it is supposed to

(D) To ensure that the sonographers are trained in calibration

(C) Ultrasound and plethysmographic equipment must have checks as part of a routine quality assurance (QA) program. QA is required for all accredited laboratories, but should be performed by nonaccredited laboratories, as well. Performing QA checks helps ensure that any error is not caused by the equipment.

When should ultrasound equipment be checked for defects in machine and/or transducers?

(A) At the end of each day

(B) During the examination

(C) On a monthly basis, as required by the accreditation bodies

(D) Before or after each patient

(D) Before a patient is scanned, the transducer and equipment should be checked to ensure there are no cracks in the transducer or cords. After the examination, it is the responsibility of the sonographer to ensure the probe cords and power cord are not run over as part of moving the equipment, and that the machine is cleaned according to laboratory standards. Annual QA checks should be performed by a biomedical technician.

What is the hazard of a cracked transducer?

(A) There is a risk that the velocities will be inaccurate

(B) There is a risk that the machine will explode

(C) There is a risk of electrical shock

(D) There is no hazard. If the probe works, it is safe

(C) Roughly 10 to 500 volts of electricity go through the transducer, presenting a potential shock hazard to sonographer and patient. Cracked transducers should immediately be taken out of service.

A phantom is designed with a string that moves through a water bath. This phantom would be used to test for (A) Pressure cuff inflation (B) Doppler-based velocities (C) Slice thickness artifact (D) Contrast resolution

(B) There are different types of Doppler phantoms. One type uses a string in a water bath to mimic flowing blood.

Five hundred patients are evaluated by conventional angiography to rule out stenosis of the internal carotid artery. You have designed a new process, called BestGuess®, which you want to compare to the “gold standard” of angiography. Of the 500 patients that had angiography, 150 were positive for stenosis by angiography. Of the 150 patients that were positive by angiography, 80 were positive by BestGuess. Of the 350 patients that were negative by angiography, 180 were negative by BestGuess.

What is the sensitivity of the new test?

The Chi square is as follows: True positives (A): 80 False positives (B): 170 False negatives (C): 70 True negatives (D): 180

Sensitivity is determined by the equation A ÷ (A + C), where A is the true positives and C is the false negatives. The answer is 80 ÷ 150 = 53%.

The Chi square is as follows: True positives (A): 80 False positives (B): 170 False negatives (C): 70 True negatives (D): 180

What is the specificity of the new test?

Specificity is determined by the equation D ÷ (D + B), where D is the true negatives and B is the false positives. The answer is 180 ÷ 350 = 51%.

the Chi square is as follows: True positives (A): 80 False positives (B): 170 False negatives (C): 70 True negatives (D): 180

What is the accuracy of the new test?

Accuracy is determined by the equation (A + D) ÷ (A + B + C + D), where A is the true positives and B is the false positives, divided by all the values in the Chi square. The answer is 250 ÷ 500 = 52%.

The Chi square is as follows: True positives (A): 80 False positives (B): 170 False negatives (C): 70 True negatives (D): 180

What is the positive predictive value of the new test?

The positive predictive value (PPV) is determined by the equation A ÷ (A + B), where A is the true positives and B is the false positives. The answer is 80 ÷ 250 = 32%.

What is the negative predictive value of the new test?

The negative predictive value (NPV) is determined by the equation D ÷ (D + C), where D is the true negatives and C is the false negatives. The answer is 180 ÷ 250 = 72%.

A test is developed that is very good at identifying a certain disease, but it only finds the disease about half the time. This test has a low \_\_\_\_\_\_ and a high \_\_\_\_\_\_ (A) Sensitivity, accuracy (B) Specificity, sensitivity (C) Accuracy, specificity (D) Sensitivity, specificity

“(B) The test described can identify a specific disease (high specificity), but it is not good at finding that disease (low sensitivity). An example of this type of test is anti-DNA for systemic lupus erythematosus (SLE). When the test is positive, it is very specific for SLE. However, the patient might have SLE and a negative anti-DNA because the test is not sensitive. In other words, the test may be negative even if the patient has active disease.