MDT160: ch 3

Card Set Information

MDT160: ch 3
2015-10-04 20:17:50

MDT160: ch 3
Show Answers:

  1. A Gaussian distribution is usually what shape ?
  2. The 3 most commonly used descriptions of the center of a data set are?
    • Mean
    • Median
    • Mode
  3. The middle point of the data that is often used with skewed data is?
  4. Rarely used as a measure of the data center, but is more often used to describe data that seem to have two centers?
  5. The mean is calculated by?
    adding up all the observed data (xi) and dividing it by the total number of data points (n)
  6. What are the sources of analytical variability?
    • Test accessories
    • Operator technique
    • Contamination
    • Instrument difference.
  7. The 3 commonly used descriptions of spread are?
    • Range
    • Standard deviation (SD)
    • Coefficient of variance (CV)
  8. The range is?
    largest data in the value minus the smallest data.
  9. the calculated average of the values is?
  10. the value for which half of the remaining values are above and half are below it. The value at the center (midpoint) of the observations is?
  11. the value that occurs most often is?
  12. How well a measurement agrees with an accepted value is known as ?
  13. How well a series of measurements agree with each other is known as?
  14. -Consider Accuracy and precision for five repeated measurements where the true value is 120. 

    -120, 120, 119, 121, 120

    What would be its validity and precision?
    • Validity: High (average is 120)
    • Precision: High (results all very close together)
  15. -Consider Accuracy and precision for five repeated measurements where the true value is 120. 

    -120, 100, 140, 90, 150

    What would be its validity and precision?
    • Validity: High (average is 120)
    • Precision: Low (results all over the place)
  16. -Consider Accuracy and precision for five repeated measurements where the true value is 120. 

    -100, 100, 99, 101, 100

    What would be its validity and precision?
    • Validity: Low (average is way off at 100)
    • Precision: High (results all very close together)
  17. -Consider Accuracy and precision for five repeated measurements where the true value is 120. 

    -100, 80, 120, 70, 130

    What would be its validity and precision?
    • Validity: Low (average is way off at 100)
    • Precision: Low (results all over the place)
  18. Measure of the scatter around the arithmetic average (mean) in a Gaussian distribution (Bell curve, or normal frequency distribution) is known as?
    Standard Deviation (SD)
  19. Precision is better when SD is?
    • Lower
    • Precision
  20. The measure of the dispersion of values around the mean, or when the standard deviation (SD) expressed as a percentage of the mean this is known as?
    coefficient of variation (CV)
  21. Precision is better when CV is?
  22. Formula for calculation V is?
    CV = (SD/mean) x 100
  23. A statistical process used to monitor and evaluate the analytical process that produces patient results is known as?
    Quality Control
  24. The overall program that ensures that the final results reported by the laboratory are correct is known as?
    Quality Assurance
  25. Measures that must be included during each assay run to verify that the test is working properly or  simply to ensure that the results generated by the test are correct would be an example of?
    Quality Control
  26. patient-like material ideally made from human serum, urine or spinal fluid.
    • quality control product or 
    • QC Material
  27. Need data set of at least 20 points
    Calculate mean, standard deviation, coefficient of variation
    Determine target ranges
    Plot results to develop Levey-Jennings charts
    Monitor control values using the Levey-Jennings chart and/or Westgard rules
    Establishing Control Ranges
  28. which Westgard Rule is violated if the QC value exceeds the mean by ±2SD.
    Warning 12SD :
  29. which Westgard Rule is violated when the QC value exceeds the mean by ±3SD.
    Rejection 13SD
  30. which Westgard Rule is violated when the difference in SD between 2 points exceeds 4SD.
    Rejection R4SD
  31. which Westgard Rule detects systematic errors and is violated when two consecutive QC values exceed the 2SD on the same side of the mean
    Rejection 22SD
  32. If 10 consecutive control measurements fall on one side of the mean.  
    If within 1 sd, warning
    If between 1 and 2 sd, reject
    Westgard Rule 10x
  33. They occur in no set pattern but represent an increase in imprecision. They can be positive or negative and fluctuate in a random manner.
    Random errors
  34. They are produced by variations that bias results consistently in one direction.
    Systematic errors
  35. The important property of a random error is?
    • It add variability to the data
    • Does not affect average performans of the group
  36. Systemic errors tent to be?
    consistently ether positive or negative.
  37. bubbles in reagents and reagent lines
    inadequately mixed reagents
    Unstable temperature and incubation
    unstable electrical supply
    operator variation in pipetting
    timing errors,
    worn tubing or syringes,
    are all examples of?
    Random errors
  38. change in reagent lot, change in calibrator lot, wrong calibrator values, improperly prepared reagents, deterioration of reagents, deterioration of calibrator, Inadequate storage of reagents or calibrators, pipet problems, change in temperature of reaction blocks, deterioration of a light source, difference in procedure between operators.
    all are examples of?
    Systemic error.
  39. the process of controlling the accuracy of an analytical method by interlaboratory comparisons is?
    Proficiency testing (PT)
  40. Most sets of PT samples are sent to participating laboratories  ____ per year.
    3 times
  41. PT testing rules are?
    • samples must be tested in the same manner you test patient specimens
    • samples should be rotated among the testing personnel in your laboratory.
  42. What is forbidden in PT testing?
    • NEVER send your PT samples to another laboratory for analysis.
    • NEVER discuss your PT results with another laboratory
    • NEVER enter into discussion with another laboratory about their PT results before the PT event cut-off date.
  43. what (calculates) shows the distance of the laboratory results from the consensus mean.
    Standard Deviation Index (SDI)
  44. SDI formula is?
    SDI =( laboratory result − Mean value of peer group) /Standard deviation of peer group
  45. what are some reasons for PT failure?
    • Analytical issues
    • Matrix Effect
    • Clerical Issues
    • Failure to send in the results
    • Sample handling
  46. what is considered Unsuccessful participation in PT?
    • Unsatisfactory performance for the same analyte in two consecutive or two out of three testing events.
    • Repeated unsatisfactory overall testing event scores for two consecutive or two out of three testing events for the same specialty or subspecialty.
  47. Precision Within run and Between runAnalytical SensitivityCalibration VerificationAnalytical Measurement Range LinearityClinical Reportable RangeClinical CorrelationInterferencesReference RangeCarry-Over Study

    All are examples of?
    Method validation studies
  48. highest apparent analyte concentration expected to be found when replicates of a blank sample containing no analyte are tested is?
    Limit of the Blank (LoB)
  49. Limit of the Blank formula is?
    LoB = meanblank + 2(SDblank)
  50. the lowest analyte concentration likely to be reliably distinguished from the LoB and at which detection is feasible is?
    Limit of Detection (LoD)
  51. what is is determined by utilizing both the measured LoB and test replicates of a sample known to contain a low concentration of analyte.
    Limit of Detection (LoD)
  52. Limit of Detection (LoD) formula is?
    LoD = LoB + 2(SD low concentration sample)
  53. the lowest concentration at which the analyte can not only be reliably detected but at which some predefined goals for bias and imprecision are met is
    Limit of Quantation (LoQ)
  54. The LoQ may be equivalent to the _______ or it could be at a much higher concentration?
  55. The range of analytical values that a method can directly measure on a specimen without dilution, concentration or other maltreatment that is not part of the usual assay process. i.e. it is the calibrated range of an assay is know as?
    Analytical Measurement Range. (AMR)
  56. the range of analyte values that a method can report as a quantitative result, allowing for specimen dilution, concentration or other pre-treatment used to extend the AMR is?
  57. What must be specified for each analyte that can be successfully diluted to bring its quantity into the AMR.
    diluent and dilution protocols
  58. Establishes the relationship between analyte content and instrument measurement signal
  59. Confirms that the current calibration settings remain valid?
    Calibration verification.
  60. Frequency of calibration or calibration verification must be?
    • at least every 6 month
    • when recommended by manufacturer
    • after major maintenance or service 
    • when QC indicates
    • at complete reagent change, unless laboratory has data showing lot uniformity
    • at change of critical reagents (defined by lab)
  61. If more than______of the results are outside of the reference limits the lab cannot use these reference limits.
    10 %
  62. performed prior to routine clinical use of all laboratory equipment in order to demonstrate that there is no carryover or carryover does not have a significant effect on test results.
    carryover assessment
  63. Carryover is considered not significant if ?
    the %carryover is <2%
  64. If the carryover is >2% you should?
    perform maintenance procedures and repeat the carryover procedure.
  65. Carryover is determined by?
    assaying a high-level sample four times in succession immediately followed by assaying a low-level sample four times in succession.
  66. Carryover is then calculated as ?
    • a percentage difference between the low sample run immediately after the high samples run.  
    • ( L1 - (L3+L4)/2)/((H3+H2)/2)-(L3+L4)/2)) * 100

    where L1, L2, L3 and L4 are the consecutive low samples and H1, H2, H3 and H4 are the consecutive high samples.
  67. The clinical performance of a laboratory test defines?
    how well it predicts disease
  68. The sensitivity of a test indicates
    the likelihood that it will be positive when disease is present
  69. The specificity of a test indicates
    the likelihood that it will be negative when disease is absent
  70. If TP as the number of “true positives”, and FP is the number of “false positives”, the sensitivity is defined as:
    (TP/TP + FN) * 100
  71. If TN is the number of “true negative” results, and FP is the number of falsely positive results, the specificity is defined as:
    ( TN/TN+FP) *100
  72. The choice of cut point depends on?
    relative adverse consequences of FN vs FP
  73. IF it is most important not to miss anyone use
    ↑ sensitivity and ↧ specificity
  74. it it is most important that people not be erroneously labeled as having the condition use?
    ↓ sensitivity ↑ specificity
  75. The predictive value of a test indicates?
    the probability that the test result correctly classifies a patient
  76. predictive value is determined by?
    • Sensitivity,
    • Specificity 
    • Prevalence of the disease
  77. Prevalence is defined as?
    the number of patients per 100,000 population who have the disease at a given time
  78. The probability of the disease being present, among those with positive diagnostic test results is know as
    Positive Predictive Value
  79. Positive predictive value (PPV) =
    TP/(TP + FP)
  80. The probability that the disease was absent, among those whose diagnostic test results were negative is
    Negative Predictive Value
  81. Negative predictive value (NPV) =
    TN/(TN + FN)
  82. A high NPV means?
    when the test yields a negative result, it is uncommon that the result should have been positive.
  83. Quality control must be monitored to assure?
    accurate reporting of laboratory test results
  84. Proficiency testing is an _______ quality control measure
  85. an important function of the laboratory is ?
    Analytical and clinical evaluation of a method