Question 1

Random error is associated with ______, and systematic error is associated with ______.The degree of ______ is described by the standard deviation or the coefficient of variation.

Accepted Answer

Random error is associated with imprecision, and systematic error is associated with inaccuracy.The degree of imprecision is described by the standard deviation or the coefficient of variation.

Question 2

In judging analytical performance in the laboratory for a new method, it was found that the 95% upper limit of an error is smaller than the allowable error.It was also found that the 95% lower limit of error is greater than the allowable error.In this situation, what should the response of the technologist be?

Accepted Answer

If the 95% upper limit of an error is smaller than the allowable error, there is at least a 95% certainty that estimated error is acceptable.If the 95% lower limit is greater than the allowable error, there is at least a 95% certainty that the error, and thus the method's performance, is not acceptable, and no further testing is indicated.The method should be rejected or modified to improve its analytical performance.

Question 3

It has been proposed that allowable error be either ______ or ______ of the reference range for an analyte, whichever is less.For enzymes, the limit is ______.

Accepted Answer

Tonks proposed that allowable error be either one fourth or 10% of the reference range, whichever is less.For enzymes, the limit is expanded to 20%.

Question 4

New analytical methods are usually developed to:
1)improve accuracy over existing methods.
2)allow automation.
3)increase labor in the laboratory.
4)reduce reagent costs.

Accepted Answer

New analytical methods are usually developed to improve accuracy or precision over
existing methods, to allow automation, to reduce reagent or labor cost, and to measure a new analyte.

Question 5

Even when a method's performance is well documented by published evaluation studies, the new laboratory considering use of the method should evaluate ______ and perform ______ to verify acceptable performance in that laboratory.

Accepted Answer

Even when a method's performance is well documented by published evaluation studies, the new user should evaluate random analytical error and perform the comparison-of-methods experiment to verify acceptable performance in that laboratory.

Question 6

A method that falls in the six Sigma region of the Medical Decision Chart indicates that the relationship between the performance of the method and quality control is such that:

Accepted Answer

Medical Decision Charts allow the relationship between method performance and quality control to be categorized based on the method's bias and imprecision.If a method's inherent errors are small relative to the CLIA '88 established allowable error, relatively weak quality-control procedures will be sufficient to detect errors that might exceed the allowable error.The six Sigma region of the chart is associated with methods that show the least inherent error.Thus the complexity of the quality-control procedures required to maintain the method's error below the allowable error is low.Specifically for six Sigma methods, one to two quality-control measures per run are required, along with a single 1₃s rule.For comparison, fair methods require four to six quality-control measures per run with the use of multiple quality-control rules.

Question 7

Usually a method-evaluation study is performed to:

Accepted Answer

Usually a method-evaluation study is not performed to test all methods to determine the method with the smallest error.Instead, these studies are used to determine whether the selected method has acceptably small analytical errors.

Question 8

Which of the following factors can contribute to random analytical errors?

Accepted Answer

Factors that contribute to random analytical error include (1) instability of the instrument, (2) variations in the temperature, (3) variations in the reagents and calibrators, (4) variability in handling techniques such as pipetting, mixing, and timing, and (5) variability in operators.

Question 9

The limit of detection:
1)is the minimum concentration of analyte whose presence can be qualitatively detected under defined conditions.
2)is the concentration at which an observed value will be very likely to exceed the limit of the blank.
3)is the highest value of a zero sample.
4)is the minimum concentration of analyte whose presence can be quantifiably measured reliably under defined conditions.

Accepted Answer

The limit of detection is the minimum concentration of analyte whose presence can be qualitatively detected under defined conditions; also the concentration at which an observed value will be very likely to exceed the limit of the blank.The highest value of a zero sample is defined as the limit of the blank.The limit of quantification is the minimum concentration of analyte whose presence can be qualitatively measured reliably under defined conditions.

Question 10

All of the following describe the within-run replication experiment except:

Accepted Answer

The interference experiment measures the constant systematic error caused by the presence of a substance suspected of interfering with the test method.The within-run replication experiment is the simplest type of study and should be one of the first performed to assess the performance of a new method.Because it allows assessment of precision over a very short time, the results cannot be extrapolated to indicate long-term performance of the method studied.The replication study should be performed with samples whose matrix is as similar as possible to that of the intended patient samples.

Question 11

When considering application characteristics, emphasis may be placed on ______ for pediatric applications, on ______ for stat applications, and on ______ for high-volume screenings.

Accepted Answer

When considering application characteristics, emphasis may be placed on sample size for pediatric applications, on turnaround time and interrupt features for stat applications, and on sample throughput rate for high-volume screenings.

Question 12

Which of the following statements is/are true regarding the correlation coefficient?

Accepted Answer

The statistic most frequently cited in reports of comparison-of-methods experiments is the correlation coefficient.A correlation coefficient of zero indicates that there is no correlation between the methods.A value of +1 indicates perfect positive correlation.Westgard and Hunt demonstrated that the correlation coefficient is extremely sensitive to the range of analyte concentrations of the patient specimens in the comparison-of-methods experiment.

Question 13

Calculate the percentage recovery given the following information:
Baseline sample preparation: 1.5 mL serum + 0.25 mL water
Spike sample preparation: 1.5 mL serum + 0.25 mL 5000 mg/L standard
Baseline sample measured concentration: 950 mg/L
Spiked sample measured concentration: 1621 mg/L

Accepted Answer

To determine the concentration of the spike added:
5000 mg/L in 1.75 mL (total volume) = 2857 mg/L in 1 mL = 714 mg/L in 0.25 mL (the actual volume added.Concentration recovered = concentration measured with spike minus baseline concentration
= 1621 mg/L - 950 mg/L
= 671 mg/L
Percent recovery = concentration recovered divided by concentration added time 100%
= 671 mg/L / 714 mg/L × 100%
= 94%

Question 14

Interference should be evaluated for all commonly encountered interferents such as:

Accepted Answer

Interference should be evaluated for all commonly encountered interferents, especially hemolysis, lipemia, and icterus.

Question 15

Regression analysis of two methods produced the equation y = 0.137 + 0.813x.The proportionality between the two methods is:

Accepted Answer

Regression analysis of two methods proven to correlate produces a line described by an equation that takes the form y = a + bx, where y and x are comparative results by the two methods, a is the y-intercept, and b is the slope of the line described by the equation.It is the slope, b, that describes the proportionality between the two methods.An ideal value for the slope is b = 1, which would indicate there is no proportionality error between the two methods.For y = 0.137 + 0.813x, the slope is 0.813.

Question 16

Which of the following is the correct sequence to follow in method selection?

Accepted Answer

The process of method selection is complex, and unless the process is well organized, method selection can be a traumatic and costly experience.The following is a logical sequence to follow in method selection: determine need, define requirements (application, methodological, performance), review literature, select candidate methods.

Question 17

The within-run component of variation is caused by:
1)sampling and pipetting precision.
2)short-term variations in temperature of the instrument.
3)instability of the calibration curve.
4)short-term variations in the stability of the instrument.

Accepted Answer

The within-run component of variation is caused by specific steps in the procedure, such as sampling and pipetting precision and short-term variations in the temperature and stability of the instrument.Within-day, between-run variation is caused by instability of the calibration curve or by differences in recalibration that occur throughout the day, longer-term variations in the instrument, small changes in the condition of the calibrator and reagents, changes in the condition of the lab during the day, and fatigue of the lab staff.

Quiz 26: Evaluation of Methods

Random error is associated with , and systematic error is associated with .The degree of __ is described by the standard deviation or the coefficient of variation.

It has been proposed that allowable error be either or of the reference range for an analyte, whichever is less.For enzymes, the limit is __.

New analytical methods are usually developed to: 1) improve accuracy over existing methods. 2) allow automation. 3) increase labor in the laboratory. 4) reduce reagent costs.

Even when a method's performance is well documented by published evaluation studies, the new laboratory considering use of the method should evaluate and perform to verify acceptable performance in that laboratory.