際際滷

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Controlling or at least
measuring
Variability In a core facility environment
Variability
 Increased variability = decreased power
 Power = probability of find an effect that is there
 You can fight this by increasing the sample size but
often it is much cheaper to decrease variability
instead
Common sources of
variability
 Biological
 Sample preparation
 Technical
 Data Analysis
What is possible in a core
facility?
 Almost no one who sends me samples has enough
money to measure variability or wants to pay for it
 What are the best ways to communicate these
issues to customers?
 How do you know what your variability is if there are
no resources to measure it?
 How do you measure variability when you have a
large number of different types experiments?
 How much QC do you bundle into your costs if you
have to charge people
Some issues I routinely
have
 Analyzing samples over months at a time.
 Sample preparation of Plant tissue may be
completely different than human cells or Plasma, or
Milk In terms of how consistently you can prepare it
 How do I know how consistently I can prepare a
sample
 Often I have no control over how the sample is
prepared. How do I deal with that?
Common ways to decrease variability
during sample prep
 Process all samples on the same day by the same
person
o Person can still get tired or make mistakesVariability may not be
consistent beginning to end
o May not be possible
 Use Robotics for part of the sample prep
o Many things still cannot be done well by robots
 In gel digestion of proteins is not optimal
 Decrease the things you do to a sample
o Fractionation, precipitation, SPE
 Label proteins or peptides upstream and multiplex
Common sources of variability you may not be
thinking about
 Pipetting errors
o Can be vary large for small volumes
 Eppendorf 2 ul = 12% Systemic 6% random error
o Hard to get tight cvs on your spiked peptides
 Variability due to SPE material lots
o The SPE material you use today may not be the same the next time you
buy it
 Variability due to software
o manual integration
o Normalization
Empirical Nulls
 Are empirical Nulls a good way to measure
variability?
Is peptide or protein
fractionation worth it?
 Does the fractionation kill your power?
 Is it better not to fractionate ?
 What is the least variable fractionation method for
proteomics?
 How do you measure the variability your
fractionation causes?
Example method to
measure variability
 From Chris Becker (Proteometrics)
Pooled
human serum
1
2
3
4
5
n
Sample aliquots
are processed
Processed samples
are pooled before
analysis and
replicates are run
Processed samples
are run individually
Sample Processing

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Phinney varibility workshop

  • 1. Controlling or at least measuring Variability In a core facility environment
  • 2. Variability Increased variability = decreased power Power = probability of find an effect that is there You can fight this by increasing the sample size but often it is much cheaper to decrease variability instead
  • 3. Common sources of variability Biological Sample preparation Technical Data Analysis
  • 4. What is possible in a core facility? Almost no one who sends me samples has enough money to measure variability or wants to pay for it What are the best ways to communicate these issues to customers? How do you know what your variability is if there are no resources to measure it? How do you measure variability when you have a large number of different types experiments? How much QC do you bundle into your costs if you have to charge people
  • 5. Some issues I routinely have Analyzing samples over months at a time. Sample preparation of Plant tissue may be completely different than human cells or Plasma, or Milk In terms of how consistently you can prepare it How do I know how consistently I can prepare a sample Often I have no control over how the sample is prepared. How do I deal with that?
  • 6. Common ways to decrease variability during sample prep Process all samples on the same day by the same person o Person can still get tired or make mistakesVariability may not be consistent beginning to end o May not be possible Use Robotics for part of the sample prep o Many things still cannot be done well by robots In gel digestion of proteins is not optimal Decrease the things you do to a sample o Fractionation, precipitation, SPE Label proteins or peptides upstream and multiplex
  • 7. Common sources of variability you may not be thinking about Pipetting errors o Can be vary large for small volumes Eppendorf 2 ul = 12% Systemic 6% random error o Hard to get tight cvs on your spiked peptides Variability due to SPE material lots o The SPE material you use today may not be the same the next time you buy it Variability due to software o manual integration o Normalization
  • 8. Empirical Nulls Are empirical Nulls a good way to measure variability?
  • 9. Is peptide or protein fractionation worth it? Does the fractionation kill your power? Is it better not to fractionate ? What is the least variable fractionation method for proteomics? How do you measure the variability your fractionation causes?
  • 10. Example method to measure variability From Chris Becker (Proteometrics) Pooled human serum 1 2 3 4 5 n Sample aliquots are processed Processed samples are pooled before analysis and replicates are run Processed samples are run individually Sample Processing