QUALITY CONTROL TECHNIQUES Flashcards
graphical representations that display the control observation as a function or time
Quality control charts
Control results are plotted on the Y-axis (ordinate)
vs time on the X-axis (abscissa)
Shewart Levey - Jennings chart
• Most widely used QC chart in the clinical
laboratory
• It easily identifies random and systematic errors
Shewart Levey - Jennings Chart
- All control values are within +/- 2 SD
• One outlier in 20 determinations
• No Trend / No Shift
In - Control
- Presence of two or more outliers
• Presence of a Trend
• Presence of a Shift
Out - of control
Uses a series of control rules for interpreting data
WESTGARD MULTIRULE CHART
Establish a criterion for judging whether an analytic
process is out of control. It recognizes that the use
of simple upper or lower quality control limit is not
enough to identify analytical problems
WESTGARD MULTIRULE CHART
- False rejection is kept low
• Error detection is improved
WESTGARD MULTIRULE CHART
One control observation exceeds +/- 2SD
12s
12s indication
Warning, result is still acceptable
2 consecutive values exceed +/- SD
22s
22s error
Systematic error
one value exceeds +/- 3SD
13s
13s error
random errror
One value exceeds +2SD and other value exceeds -2SD
R4s
R4s error
random error
4 consecutive values exceed +/- 1SD
41s
41s error
Systematic error
10 consecutive values fall on one side of the mean
10x
10 x error
Systematic error
- Goes beyond monitoring, detecting, and preventing errors.
• Achieves new levels of performance through quality control, and addresses chronic problems.
Quality improvement
Hands-on process with the single mantra of
“improvement” – this is a performance to improve the program in which the goal is to improve the
process by eliminating variations of errors.
Six sigma
Improved in six sigma
- performance
- quality
- bottom line
- customer satisfaction
- employee satisfaction
It measures the degree of variability or error in products or services through statistics and quantitative parameters
Six sigma
A tool that can be used to reduce laboratory errors, increase productivity and improve quality in the clinical laboratory
six sigma
main goal of sigma
to reduce the number of defects to near zero
What is measured in six sigma
Defects per million opportunities
Anything that does not meet customer requirements
Defect
Goal of six sigma
3.4 DPMO or 99.9997% yield
It calculates the difference between quality control
results and target means
Cumulative chart
common methods of cusum
v-mask
It identifies consistent bias problems; it requires
computer implementation
CUSUM chart
This plot will give the earliest indication of systemic errors (trend) and can be used with the 13s rule
CUSUM chart
found in clinical laboratories with microcomputer quality control programs found in clinical laboratories with microcomputer quality control programs
Decision limit CUSUM
Very sensitive to systematic errors but does not
provide very good detection of random errors
Cumulative Sum chart
The results are out of control when the slope exceeds
45 degrees Celsius or a decision (+/- 2.7 SD) is exceeded
very sensitive to small persistent error that commonly occur in the modern low calibration frequency analyzer
CUSUM graph
this is a consistent, repeatable error with faulty equipment or flawed experiment design
Systematic error
caused by unknown and unpredictable changes in the experiment
Random error
Also known as scatter diagram
Youden plot/ twin plot
It is used to compare results obtained on a high and low control serum from different laboratorie
Youden plot or twin plot
Information about the nature of the systematic error can be obtained when two different control materials have been analyze
Youden plot/ twin plot
*Presents information in an efficient, graphical
format
• Structured prepared form for collecting and
analyzing data
Check sheet
• Accomplished with a simple listing of items
• The data can either be quantitative or qualitative in nature
• Its use may be enhanced by incorporating a
depiction of the system under analysis into the Form
Check sheet
*Analyzes the frequency of problems or causes in the process
• Used to identify factors that have the greatest
cumulative effect on the system
Pareto chart
*Allows the user to focus attention on a few
important factors in a process
• Cumulative frequencies of the relative frequency
data are plotted in descending order
Pareto chart
In pareto chart, Cumulative frequencies of the relative frequency data are plotted in What order?
Descending
Pareto chart is named after
Vilfredo Pareto
This is a type of chart that contains both bars and
line (cumulative total)
Pareto chart
Cause and effect diagram is also known as
Ishikawa or fishbone diagram
A visual tool used to logically organize possible
causes for a specific problem or effect by
graphically displaying them in an increasing detail
suggesting causal relationships among theories
Cause and effect diagram
Used to associate multiple possible causes with a
single effect
Cause and effect diagram
represents the effect (quality characteristic that is intended to be improved and controlled)
Primary branch
corresponds to major causes that directly relates to the effect
Major branches
more detailed causal factors
Minor branches
*Pictorial representation of a process
• Used in identifying where errors are likely to be
found in the system
Flow chart
*Provides a simple, graphical view of accumulated
data, including its dispersion and central tendency
• Ease of construction
• Provides the easiest way to evaluate the distribution of data
Histogram
This is a graphical display of data using bars of different heights. It is similar to a bar chart but groups of numbers in this are groups of
numbers that are in ranges
Histogram
Most commonly used graph to show frequency
distributions
Histogram
A control value that goes beyond +/- 2SD
Outlier
Causes of an outlier
-contamination of a single specimen
-faulty pipette
-incorrect dilution of test
