Control charts to trend data for multiple dependent variables? Hotelling's T^2 stat

D

Dan Armstrong

#1
Multi-variable control charts?

Is it possible to use control charts to trend data for multiple dependent variables?
I need to trend the water conductivity for a purified water system, which wouldn't normally be a problem, except the specifications (USP - US Pharmacopeia) state that the conductivity measurement cannot be temperature compensated. The conductivity limit varies directly with increasing temperature.
How can I trend the data when the limit for one variable changes based on another variable?
 
Elsmar Forum Sponsor

Darius

Quite Involved in Discussions
#2
Dan Armstrong said:
Is it possible to use control charts to trend data for multiple dependent variables? ....
The conductivity limit varies directly with increasing temperature.
How can I trend the data when the limit for one variable changes based on another variable?
It may be a nonesense but...

If the conductivity depends on the temperature, you can determinate the target and limits of the conductivity chart and change them acording to the temperature, or use "Short Run Charts", where each point is (IX - Taget_IX/Target_MR).
 
G

Graeme

#3
Dan Armstrong said:
Is it possible to use control charts to trend data for multiple dependent variables?
...
How can I trend the data when the limit for one variable changes based on another variable?
Another way to do this is to use a multivariate control chart such as one based on Hotelling's T^2 statistic. It is a bit complex to go into here, but there are a number of Internet sites that discuss it. For example, see the NIST page at http://www.itl.nist.gov/div898/software/dataplot/refman1/auxillar/hotell.htm or the NIST online statistics handbook at http://www.itl.nist.gov/div898/handbook/index.htm

Also, it appears that some statistical software programs have this built in, because a search for "hotelling" and "control chart" produced hits from companies such as Statsoft and Minitab.
 
Thread starter Similar threads Forum Replies Date
G Control charts where the center line is a trend or slope? Statistical Analysis Tools, Techniques and SPC 26
U Electronic templates for making paper control charts Reliability Analysis - Predictions, Testing and Standards 2
Rameshwar25 Other types of Control Charts described in Chapter II of SPC Manual Statistical Analysis Tools, Techniques and SPC 6
S Standard Deviation Selection on Control Charts - Minitab "pooled deviation" Statistical Analysis Tools, Techniques and SPC 3
N Injection Molding - Median individual control charts Statistical Analysis Tools, Techniques and SPC 6
Chennaiite Do Attribute Control Charts really help? Statistical Analysis Tools, Techniques and SPC 9
B Setting Lower Control Limit on Attributes Charts Statistical Analysis Tools, Techniques and SPC 9
M Interpreting X bar and R Control Charts Statistical Analysis Tools, Techniques and SPC 2
M Large Sample Size - up to 32 - for Control Charts Capability, Accuracy and Stability - Processes, Machines, etc. 2
T Is the use of Control Charts Mandatory or Optional? ISO 17025 Requirements ISO 17025 related Discussions 6
E Minitab for hourly patient census - Control Charts Using Minitab Software 6
J Using P-Charts for Glass Manufacturing to Monitor and Control Attributes Statistical Analysis Tools, Techniques and SPC 2
M On Subgroups in Control Charts and Process Capability Statistical Analysis Tools, Techniques and SPC 3
S Help with Table of Constants and Formulas for Control Charts Statistical Analysis Tools, Techniques and SPC 5
Q Monthly Data Review through Control Charts - Monitoring Complaints ISO 13485:2016 - Medical Device Quality Management Systems 3
R "Control" as used in 4.1 c) - Process Flow Charts (Process Sequence Chart) ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
D Suitability of Attribute Control Charts for ppm Level Control Statistical Analysis Tools, Techniques and SPC 6
R Metrology Control Charts for Reference and Working Standards General Measurement Device and Calibration Topics 6
D One-Two-Three Sigma Control Limits - Calculating Control Limits for X-bar Charts Statistical Analysis Tools, Techniques and SPC 3
bobdoering Myth or Mythunderstanding: Implications of the Economic Design of Control Charts Statistical Analysis Tools, Techniques and SPC 1
E Performance Charts - Purchasing Department and Material Control Department Preventive Action and Continuous Improvement 6
J Control Charts for 29 Devices that I tested Reliability Analysis - Predictions, Testing and Standards 10
J Control Charts with different Sample Sizes Reliability Analysis - Predictions, Testing and Standards 2
T why CPK <1.0 regarding two pieces of control charts of torque wrench? Statistical Analysis Tools, Techniques and SPC 2
R Electronic Templates for making Paper Control Charts Document Control Systems, Procedures, Forms and Templates 9
S Multivariate Control Charts in Chemical Batch Processing Statistical Analysis Tools, Techniques and SPC 7
G Control Charts - Plotting Unwanted Data Excel .xls Spreadsheet Templates and Tools 5
Y Control Charts + Ishikawa Manufacturing and Related Processes 26
N SPC Light Program - Easy way of Cpk extraction from multiple control charts Statistical Analysis Tools, Techniques and SPC 4
K Calculating Control Limits in Average and Range Charts Statistical Analysis Tools, Techniques and SPC 3
G Adjusted Control Limits - Usage of Control Charts Statistical Analysis Tools, Techniques and SPC 26
U P Charts - Subgroup Sizes? Process Control Indicator Statistical Analysis Tools, Techniques and SPC 3
E Which control charts to monitor waste produced on the shop floor Statistical Analysis Tools, Techniques and SPC 5
J Control limits for one sided control charts using WECO rules Statistical Analysis Tools, Techniques and SPC 5
T Rules for interpreting control charts Statistical Analysis Tools, Techniques and SPC 2
G Control charts of finished product characteristics..NonSense? Statistical Analysis Tools, Techniques and SPC 8
D Control limit calculation (Xbar R charts) using Minitab Statistical Analysis Tools, Techniques and SPC 14
H How to create Stoplight Control charts with excel? Excel .xls Spreadsheet Templates and Tools 16
sathis Calculating 1 sigma and 2 Sigma limits in Control Charts Statistical Analysis Tools, Techniques and SPC 1
M Control Charts - Points TOUCHING Limits = Stable? Statistical Analysis Tools, Techniques and SPC 12
T What is Average Run Length & Average Production Length when used in Control Charts? Statistical Analysis Tools, Techniques and SPC 4
T Using SPC Control Charts to Reduce AQL Sample Size AQL - Acceptable Quality Level 16
B Recommendation for a book to Explain Control Charts Book, Video, Blog and Web Site Reviews and Recommendations 6
C Designing Control Charts - Variable with Small Variation and Tight Control Limit Statistical Analysis Tools, Techniques and SPC 20
K Understanding Control Charts Methodology for Attributes like Plug Guages. Statistical Analysis Tools, Techniques and SPC 1
J Selection Procedure for the Use of Control Charts (Apendix C) Statistical Analysis Tools, Techniques and SPC 2
B Reaction to Out of Control SPC Charts Statistical Analysis Tools, Techniques and SPC 14
J Run Charts and Alternative Process Control Parameters Statistical Analysis Tools, Techniques and SPC 5
Steve Prevette Example SPC Control Charts posted by the Department of Energy EFCOG Statistical Analysis Tools, Techniques and SPC 1
B Why is the Mean preferred over Median in Control Charts? Statistical Analysis Tools, Techniques and SPC 12

Similar threads

Top Bottom