a note on precision of qualitative data
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A note on precision of qualitative data. Tomomichi Suzuki, Tokyo University of Science [email protected] Yusuke Tsutsumi, Mitsubishi Tanabe Pharma Corporation Natsuki Sano, Tokyo University of Science. Introduction of myself. - PowerPoint PPT PresentationTRANSCRIPT
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A note on precision of qualitative data
Tomomichi Suzuki, Tokyo University of Science [email protected]
Yusuke Tsutsumi, Mitsubishi Tanabe Pharma Corporation
Natsuki Sano, Tokyo University of Science
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Introduction of myself
• I focus on “Statistical Data Analysis” that will bridge the gap between theory and practice.
• I am attending ISQC for the fourth time• Warsaw 2004, “Effective Dynamic Process Control of Assembly
Processes”– statistical control of assembly process with time dependent noise
• Beijing 2007, “A Study on Adaptive Paired Comparison Experiments”– design of experiment for paired comparison– proposal on the Swiss tournament system
• Seattle 2010, “Improving Taguchi’s linear graphs for split-plot experiments”– proposed new linear graphs for expressing interaction of whole-plots
and sub-plots
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Outline of Today’s Talk
• Introduction
• Precision for Quantitative Data
• Precision for Qualitative Data
• Comparison
• Conclusions
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Outline of Today’s Talk
• Introduction
• Precision for Quantitative Data
• Precision for Qualitative Data
• Comparison
• Conclusions
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Introduction
• ISO 5725 accuracy (trueness and precision) of measurement methods and results
• Tests performed on presumably identical materials in presumably identical circumstances do not, in general, yield identical results.
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Introduction
• ISO 5725 accuracy (trueness and precision) of measurement methods and results
• Trueness:– refers to the closeness of agreement between
the arithmetic mean of a large number of test results and the true or accepted reference value.
• Precision:– refers to the closeness of agreement between
test results.
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ISO/TC 69/SC 6
• ISO/TC 69 (Application of Statistical Methods)/SC 6 (Measurement Methods and Results)/WG1 (Accuracy of measurement methods and results) is preparing a document (TR: Technical Report) on precision of qualitative data. Now in Preliminary Work Item.
• Reviewed existing methods and established methods.
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ISO/TC 69/SC 7
• ISO/TC 69 (Application of Statistical Methods)/SC 7 (Six Sigma) published ISO TR 14468 “Selected illustrations of attribute agreement analysis”
• This is based on kappa coefficient approach.
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ISO/TC 34/SC 9
• ISO/TC 34 (Food products) /SC 9 (Microbiology) produced ISO 16140 “Microbiology of food and animal feeding stuffs — Protocol for the validation of alternative methods” in 2003.
• It includes method by Langton et al. (2002)• ISO/TC 34/SC 9 is revising ISO 16140
“Microbiology of food and animal feed — Method validation — Part 2: Protocol for the validation of alternative (proprietary) methods against a reference method”.
• It includes method by Wilrich.
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AOAC InternationalISO/TC 34/SC 16
• ISPAM (International Stakeholder Panel on Alternative Methods) produced a document on “Guidelines for Validation of Qualitative Chemistry Methods” which is based on POD model proposed by P. Wehling et al. (2011)
• This is the main part of the ISO/TC 34 (Food products) /SC 16 (Horizontal methods for molecular biomarker analysis) document. “Validation Scheme for Qualitative Analytical Methods” (possible alternative title: "Performance characteristics and validation of binary measurement methods")
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IMEKO/TC 21
• IMEKO (International Measurement Confederation) / TC 21 (Mathematical Tools for Measurements) hold SIG (Special Interest Group) “Precision evaluation in non-quantitative measurements”.
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Purpose
• Many methods are proposed for qualitative data, but their effectiveness and statistical properties are not so clear.
• This paper introduces the methods to evaluate precision for qualitative data, then proposes a method using logit model. The proposed method is compared with existing methods.
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Outline of Today’s Talk
• Introduction
• Precision for Quantitative Data
• Precision for Qualitative Data
• Comparison
• Conclusions
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Collaborative Assessment Experiment
Laboratory Run 1 ... Run k ... Run n
1 y11 y1k y1n
2 y21 y2k y2n
:
:
i yi1 yik yin
:
:
L yL1 yLk yLn
• Every laboratory measures the identical test item number of times.
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Precision for Quantitative Data
• Repeatability:– is the precision under repeatability conditions– where independent test results are obtained with the same
method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time.
– Repeatability indicates the smallest variation for a particular measurement method.
• Reproducibility:– is the precision under reproducibility conditions– where test results are obtained with the same method on
identical test items in different laboratories with different operators using different equipment.
– Reproducibility indicates the largest variation for a particular measurement method.
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Precision for Quantitative Data
• Model used in ISO 5725
y = m + B + e
– y is the measurement result– m is the general mean (expectation)– B is the laboratory component of bias under
repeatability conditions (variance L2)
– e is the random error in every measurement under repeatability conditions. (variance e
2)16
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Precision for Quantitative Data
• Repeatability variance r2
r
2 = e2 , or
• Reproducibility variance R2
R2 = L
2 + r2 = L
2 + e2 , or (1)
• The estimates of repeatability variance and
reproducibility variance are calculated from interlaboratory studies or collaborative assessment experiments.
)(eVr
)()( eVBVR
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Precision for Quantitative Data
• Gauge R & R• Many objects are measured (there are variation in products)
• Gauge Repeatability = Repeatability in ISO 5725 (r2)
• Gauge Reproducibility ≠ Reproducibility in ISO 5725
• Gauge Reproducibility = Between Laboratory Variance in ISO 5725 (L
2) R
2 = L2 + r
2 (1)
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Outline of Today’s Talk
• Introduction
• Precision for Quantitative Data
• Precision for Qualitative Data
• Comparison
• Conclusions
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Precision for Qualitative Data
• Non-quantitative measurements– binary data, categorical data, ordinal data, etc.
• In this paper, the methods to evaluate precision for binary data are considered.
• Methods compared are– Accordance and concordance (Langton’s)– Attribute agreement analysis (Kappa)– van Wieringen’s method– Proposed method
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Precision for Quality Data
Laboratory Run 1 ... Run k ... Run n
1 y11 y1k y1n
2 y21 y2k y2n
:
:
i yi1 yik yin
:
:
L yL1 yLk yLn
• The value of yik is either 0 (negative, non-detect, fail, etc.) or 1 (positive, detect, pass, etc.).
Table 1
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Qualitative Methods0. ISO Based Method
ijiij ey Wilrich’s model
eBmy ISO5725 model
i
ije
: general mean
: laboratory component of bias: random error
Repeatability Variance
Inter-laboratory Variance Component
Reproducibility Variance
L
iiir Ln
n
1
2 ˆ1ˆ1
1ˆ
L
i
L
iiiiL LnL 1 1
22 ˆ1ˆ1
1
1ˆˆ
1
1,0maxˆ
222 ˆˆˆ LrR
: Estimate of probability of detecting for lab i (i=1, 2, …, L)
i
n : number of repetitions (measurements)
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Qualitative Methods1. Accordance and Concordance
Accordance1
1
1
1
0
Lab i
matching probability Ai
)1(
)1)(()1(
nn
xnxnxxA iiii
i
L
iiA
LA
1
1
iA
A
: Accordance for laboratory i (i1, 2, ..., L)
: Accordance
nix : number of ‘detect’ for lab i (i1, 2, ..., L): number of repetitions (measurements)
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Qualitative Methods1. Accordance and Concordance
)1(
)1(12
211
LLn
nnLAnLnLnLxx
Ci
L
ii
L
ii
i
L
iiC
LC
1
1
iA
C : Concordance
iC
Concordance 11
1
1
0
lab i
11
1
1
1
lab i’matching probability Ci
10
0
1
1
lab i’’
: Accordance for laboratory i (i1, 2, ..., L)
: Concordance for laboratory i (i1, 2, ..., L)
nix : number of ‘detect’ for lab i (i1, 2, ..., L): number of repetitions (measurements) 24
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Qualitative Methods1. Accordance and Concordance
• Relation between ISO based method and accordance, concordance
25725:ˆ
2
1basedISOr
A
25725:ˆ
2
1basedISOR
C
AccordanceA : eConcordancC :
,
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Qualitative Methods2. Van Wieringen et al(2008)
・ binary 1: detect, pass 0: no-detect, fail
Sensitivity
Specificity
hj
iijhilmiii YXPYXXXP,
,,2,1,1,1, ,...,,lhmjni ,...,1,...,1,...,1
items appraisers repetitions
model
ijhX
iY: measurement
: true value
)1( iYP
yYXPy iijhj 1
true probability of ‘pass’
1j
01 j
xj
xjijh xXP 1)0(1)0(1 x
jx
j 1)1(1)1(
where
latent class model
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Qualitative Methods2. Van Wieringen et al(2008)
l
h ijhij XR1
Tmm 0,...,0,1,...,1, 11 Likelihood when
n
i
Rj
Rlj
m
j ij
ijij
R
lRL
1 1
0011;
ijij R
jRl
j
m
j ijR
l111
1
Maximum Likelihood Estimate using EM algorithm Maximum Value:
where
n
i
Rj
Rmlj
i
ii
R
mlRL
1
0011;
i
Rj
Rmlj R
mlii 111
Likelihood when )0()0(1 m )1()1(1 m and
RRL
Maximum Likelihood Estimate using EM algorithm Maximum Value: RL27
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Qualitative Methods2. Van Wieringen et al(2008)
Repeatability
Reproducibility
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Qualitative Methods3. Attribute Agreement Analysis
Fleiss’ Kappa Statistic
e
eo
P
PPˆ1
ˆˆˆ
n
i
M
jijo nmx
mnmP
1 1
2
)1(
1ˆ
M
jje pP
1
2ˆ
oP
eP
jp
n
m
M
ijx
: Probability that results actually matched: Probability that results match by chance
: number of item i categorized as j
: number of items: number of appraisers
: Ratio of category j : number of categories
11 complete agreement the same as chance (no correlation)complete non-agreement
within appraisers between appraisers 29
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Qualitative Methods4. Proposed Method
• We propose the method of estimating repeatability and reproducibility using the logit transformation.
• When the number of positive results xi follows a binomial distribution with parameters n and pi, then logit transformation of pi
* asymptotically follows a normal distribution as follows.
(4)
where and
iii
ii n
NL
1
1,
1ln~
*1
*ln*
i
iii LogitL
1
5.0*
n
xii
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Qualitative Methods4. Proposed Method
• When we consider xi as the measurement result of laboratory i, the variances can be estimated by means of one-way ANOVA as shown below.
• Repeatability Variance
(6)• Reproducibility Variance
(7)
L
i iir nL 1
2
ˆ1ˆ11
ˆ
LLLL
L
ii
L
iiR
2
11
22
1
1
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Outline of Today’s Talk
• Introduction
• Precision for Quantitative Data
• Precision for Qualitative Data
• Comparison
• Conclusions
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Comparison of methods
• Methods are compared using the same set of data in order to clarify the relation of among the methods.– Accordance and concordance,– Attribute agreement analysis (Kappa)– van Wieringen’s method– Proposed method
• We compared the methods by averaging the obtained precision measures in the case for Langton's method and the proposed method.
• The parameters are set based on van Wieringen's method.
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Comparison of methods
• Values of parameters (of figures next page)– overall (probability of an item being
conforming): 0.5– number of items: 200– number of raters L: 3– number of repetitions for each rater n: 3– probability of evaluating conforming item as pass:
0.99, 0.95, 0.90– probability of evaluating nonconforming item as
pass: 0.01, 0.05, 0.10(those probabilities are for raters 1 to 3
respectively)34
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Comparison of methodsResults
• Repeatability(above) and Reproducibility(below)
• Strong relation among the methods. But not identical.
1000
1050
1100
1150
1200
1250
1300
0.83 0.84 0.85 0.86 0.87 0.88 0.89
van
Wie
ringe
n(r)
Accordance
0.67
0.68
0.69
0.70
0.71
0.72
0.73
0.74
0.75
0.76
0.83 0.84 0.85 0.86 0.87 0.88 0.89
κ w
ithin
rate
rs
Accordance
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9
11.0
0.83 0.84 0.85 0.86 0.87 0.88 0.89
logi
t(r)
Accordance
0
20
40
60
80
100
120
140
0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89
van
Wie
ringe
n(R)
Concordance
0.66
0.68
0.70
0.72
0.74
0.76
0.78
0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89
κ be
twee
n ra
ters
Concordance
6.95
7.00
7.05
7.10
7.15
7.20
7.25
7.30
7.35
7.40
7.45
0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89
logi
t(R)
Concordance
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Comparison of methodsResults
• Accordance and concordance, attribute agreement analysis and the proposed method gave very similar results.
• The method proposed by van Wieringen also gave similar results but the relationship was not as strong.
• The reason for giving different precision measures should be investigated.
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Outline of Today’s Talk
• Introduction
• Precision for Quantitative Data
• Precision for Qualitative Data
• Comparison
• Conclusions
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Conclusions
• The method utilizing logit transformation is proposed.• The proposed method and other existing methods are
compared using the same set of data.• Accordance and concordance, attribute agreement
analysis and the proposed method gave very similar results.
• The method proposed by van Wieringen also gave similar results but the relationship was not as strong.
• Other methods (POD models etc.) should also be compared. How to compare is the problem.
• It would be expected that these findings contribute to standardization of evaluating precision of binary measurements. 38
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References• Danila O., Steiner, S. H., and Mackay R. J. (2008). Assessing a
Binary Measurement System. Journal of Quality Technology, 40, 310-318.
• Fleiss, J. L. (1981). Statistical Methods for Rates and Proportions. 2nd edition, John Wiley & Sons.
• Horie K., Tsutsumi Y., Suzuki T. (2008). Calculation of Repeatability and Reproducibility for Qualitative Data. Proc. 6th ANQ Congress, 12 pages (CDROM).
• ISO 5725 (1994). Accuracy (trueness and precision) of measurement methods and result – Part 1 : General principles and definitions.
• ISO 5725 (1994). Accuracy (trueness and precision) of measurement methods and result – Part 2 : Basic methods for the determination of repeatability and reproducibility of a standard measurement methods.
• ISO/TR 14468 (2010). Selected illustrations of attribute agreement analysis.
• Langton, S.D., Chevennement, R., Nagelkerke N., and Lombard B. (2002). Analysing collaborative trials for qualitative microbiological methods: accordance and concordance. International Journal of Food Microbiology, 79, 175-181.
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References• Mandel, J. (1997). Repeatability and Reproducibility for Pass/Fail
Data. Journal of Testing and Evaluation, 25, 151-153.• Van der Voet, H. and van Raamsdonk L. W. D. (2004). Estimation of
accordance and concordance in inter-laboratory trials of analytical methods with qualitative results. International Journal of Food Microbiology, 95, 231-234.
• Wehling, P., LaBudde, R.A., Brunelle, S. L., and Nelson, M. T. (2011). Probability of Detection (POD) as a statistical model for the validation of qualitative methods. Journal of AOAC International, 94, 335-347.
• Van Wieringen, W. N., and de Mast, J. (2008). Measurement System Analysis for Binary Data. Technometrics, 50, 468-478.
• Wilrich, P.-Th. (2010). The determination of precision of qualitative measurement methods by interlaboratory experiments. Accreditation and Quality Assurance, 15, 439-444.
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Thank you for your attention!
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