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42 Cards in this Set
- Front
- Back
Mean |
- the average of a group of numbers - symbol is X bar - use the mean value to perform other statistical tests on the group - one indicator of "central tendency" |
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Central Tendency |
- distribution of data around a central value |
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Median |
- indicator of central tendency - central number in a group of numbers when the numbers are arranged in sequential order - an equal quantity of numbers is greater than the median value and less than the median value - may or may not be the same as the mean |
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Mode |
- the number that occurs most frequently in a group of numbers - there is bimodal, trimodal, etc. |
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Indicators of Central Tendency |
- Mean and median |
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Accuracy |
- correctly reflects the "true value" of the result - imagine a "target" value that should be obtained for an analyte |
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Precision |
- occurs when, after repeated analysis, the same result is achieved |
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In the lab, how accurate and precise do we want to be? |
- we want results that are both accurate and precise - when a method is both accurate and precise, it is reliable |
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Sensitivity |
- a quality of a method that allows for the detection of very small amounts of analyte in a sample |
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Specificity |
- the quality of an analytical method to discriminate the analyte of interest from other substances present in the sample |
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Variance |
- indicator of the precision of a group of numbers - symbol is s squared - indicates how close together, or how precise, the numbers within a group are - a group of numbers with a large variance would be expected to have a wide range of values - a group of numbers with a small variance would be expected to have numbers that are very close in value - the smaller the variance a group of numbers, the more precise they are - how we measure precision |
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Standard Deviation |
- the most frequently used measure of precision - symbol: s - square root of the variance |
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Probabilities Associated with Standard Deviation |
Statistically, if a sample is analyzed 30 times and the mean and SD established for the results are: - 68.2% of the time, the results will fall within plus or minus 1 SD from the mean - 95.5% of the time, the results will fall within plus or minus 2 SD from the mean - 99.7% of the time, the results will fall within plus or minus 3 SD from the mean - 68-95-99.7 rule |
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Standard Deviation Range |
Measurement of "dispersion"; calculated by: - subtracting the standard deviation value from the mean value to establish the lowest number in the range - adding the SD value to the mean value to establish the highest number in the range - established for qc material by the lab as method of setting acceptable qc limits. Frequently 1, 2, and 3 SD are established |
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Coefficient of Variation |
- useful when comparing two or more groups of data to determine which has the greatest precision - the lower the coefficient of variation is for a group of data, the more precise the data |
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QC Material |
- material that is analyzed along with the patient specimens and should be treated the same as patient specimens - should be of the same matrix as the patient sample |
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QC Material (Matrix) |
- the chemical and physical characteristics of the material that contains the analytes to be measured - components of a sample other than the analytes of interest |
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QC Analysis - Are results reported if QC is outside of the acceptable limit esablished by the lab? Should you still report if the method is out of control |
- if the qc result is outside of the acceptable limit established by the lab, the patient results should not be reported until the problem is solved - no patient results should be reported until the method is "in control." |
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Errors that cause a method to be out of control |
- Out of control means a result outside of established QC range Two main reasons why a method is out of control - Random error occurs solely by chance. Related to the precision of the method. More complicated method, more chances of random error - Systematic error. All samples affected. May produce a "bias" in the method. related to the accuracy of the method. Instrument problem |
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Measures of Precision |
- Variance - Standard Deviation |
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Levey-Jennings Chart |
- To analyze each qc value, plot the value on a Levey-Jennings chart |
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CLIA'88 and good lab practices require how many QC's before patient results are reported |
- require at least 2 QC materials/day for each nonwaived method |
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Shifts |
- occurs when QC results are all distributed on side of the mean for 5 to 7 consecutive days - occurs because of systematic error - cause must be found and corrected because the method is "out of control" - a shift can be positive or negative |
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Trends |
- occurs when QC results either decrease or increase consistently over a period of 5 to 7 days - is due to systematic error - trends occur more slowly - cause must be found and corrected - a trend can either be positive or negative |
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What error causes shifts and trends? |
- Systematic error |
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Westgard Multirules (1 two s Rule) |
- rule is violated if either of the 2 controls exceeds 2 SD from the mean in either a positive or negative direction - when this rule is violated, the other rules are applied - if the qc results do not violate any other rule, even if one of the 2 results violates the 1 two s rule, the control results are accepted |
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Westgard Multirules (1 three s rule) |
- violated when the result is one of the 2 qc results is outside of 3 SD - if a result is outside of 3 SD, less than 1% chance that the result is an accurate result. 99.7% chance the result is an outlier - when either of the QC results violates this rule, the result is rejected. run is out of control and should not be accepted. - usually due to random error. |
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Westgard Multirules (2 two s rule) |
- can be violated in 2 ways - if both control results are >2 SD or <2 SD from the mean - if one of the control results also exceeded 2 SD in the same manner in the previous run - does not violate the 1 three s rule |
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Westgard Multirules (R four s rule) |
- violated when the difference, or range, between the 2 control values within a run is >4 SD - violated when both control values violate the 1 two s rule but in opposite directions. one control is elevated higher than the +2 SD limit and the other is less than -2 SD limit. - usually violated due to random error |
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Westgard Multirules (4 one s rule) |
- Can be violated in two ways. one level of control: 4 consecutive results fall on the same side of the mean and exceed plus or minus 1 SD of the mean. two levels of control: when both levels of control for 2 runs in a row exceed plus or minus 1 SD from the mean - somewhat like the rule for a shift. the 4 results are on the same side of the mean (which is statistically unlikely) and exceed 1SD (but not 2SD). |
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Westgard Multirules (10 x Rule) |
- Can be violated in 2 ways. in 10 consecutive runs for one level of qc, the results are all on the same side of the mean. the 10 results can fall in either a positive or negative direction. - when the results are all on the same side of the mean for both levels of control for 5 days (or 5 runs) in a row. |
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Preventive Maintenance |
- instrument component maintenance - corrective maintenance - wide range of components needing maintenance - Maintenance schedule prevents breakdown - maintenance program prescribed by manufacturer and supported by agreement depending on instrument complexity |
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Maintenance vs Repair |
- keep components in OEM (original equipment manufacturer) condition - prevent failure - perform maintenance procedures correctly as set forth by the manufacturer - maintain physical integrity in as new condition - Daily-Weekly-Monthly and as needed - keep records of functions by date and person performing function |
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Pm (Preventative Maintenance) and its impact on QC |
- proper function and performance - owner/operator functions - maker functions - operator training - alignments - adjustments and mfg. specs - proper replacement procedure |
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Manufacturer Service Contracts |
- complex instruments must have Mfg. (manufacturer) support - 24 hour availability to service - lab operation and ability to provide critical service - regulatory considerations - documentation of due care |
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PM program |
- functions - schedules - documents - required by regulatory agencies - ongoing process - required commitment of time and money - performance is planned and scheduled event that is a documented part of work |
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Phases of Patient Care |
- pre analytical is everything that occurs with patient prior to actual analysis of sample - analytical is process where specimens are being analysed - post analytical is what the doctor does with the data produced |
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Customer Expectations |
- who is the customer? - health care provider is the customer's agent - provider/doctor/practitioner are employees of the patient - providers employs other sub providers - courtesy, respect, and expectation of good outcome - top quality in process - competency expected and required |
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Provider Expectations |
- accuracy - complete order filled to their satisfaction - happy patient with a favorable outcome - results is a clinically relevant time frame - speed and accuracy |
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Corporate Expectations |
- profit - cost - shareholders - stock price - low overhead - no bad publicity |
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Expectations |
- different from each point of view - a happy patient that got better - condition improved |
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Care Delivery System |
- accessing and acquiring of information/communication - diagnostic data development and accumulation through imaging, lab and other vehicles - planning or development of care plan based on accumulated data - treatment or the implementation of care plan - evaluation of process for improvement (QA) |