ITMF, ICCTM
Stickiness Working group
Quality criteria of measurements
based on counts
Bremen, April 1, 2008
Gozé E., Gourlot J.-P., Lassus S., Frydrych R.
Annual cropping systems research unit, CIRAD
Quality criterion of measurements
based on counts
Useful measurement must be
1 correlated to practical properties of the
analyzed material
2 reproducible
Measurements are variable
Variability => risk in decisions
need of criteria to measure variability : e.g. CV=5%
Is a single figure of standard deviation or a CV useful
for count data? Is a 5% CV a good benchmark ?
Outline
• Variability of some defects measurements
on yarn and fiber
• Known probability distributions as
theoretical landmarks
• Some practical recommendations to
evaluate precision + discussion
• Variability of some defects measurements
on yarn and fiber
• Known probability distributions as
theoretical landmarks
• Some practical recommendations to
evaluate precision + discussion
200% Neps on yarn
5 s a m p l e s o f 2 0 0 m p e r y a r n S t a n d a r d D e v i a t i o n 3 4 5 6 7 8 9 1 0 1 1 1 2 M e a n 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 (Cirad laboratory)200% Neps on yarn
5 s a m p l e s o f 2 0 0 m p e r y a r n C V ( % ) 0 1 0 2 0 3 0 4 0 M e a n 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 (Cirad laboratory)200% Neps on yarn
5 s a m p l e s o f 2 0 0 m p e r y a r n L o g N ( 1 + V a r i a n c e ) 2 3 4 5 L o g N ( 1 + M e a n ) 2 . 6 2 . 8 3 . 0 3 . 2 3 . 4 3 . 6 3 . 8 4 . 0 4 . 2 4 . 4 (Cirad laboratory)200% Neps on yarn
5 s a m p l e s o f 2 0 0 m p e r y a r n L o g N ( 1 + V a r i a n c e ) 2 3 4 5 L o g N ( 1 + M e a n ) 2 . 6 2 . 8 3 . 0 3 . 2 3 . 4 3 . 6 3 . 8 4 . 0 4 . 2 4 . 4 (Cirad laboratory)Poisson distribution :
Variance=mean
Afis n ASTM D 5866
r e p e a t a b i l i t y w i t h i n l a b o r a t o r i e s C V ( % ) 0 1 0 2 0 3 0 4 0 5 0 6 0 M e a n 0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0Afis n ASTM D 5866
r e p e a t a b i l i t y w i t h i n l a b o r a t o r i e s L o g N ( 1 + V a r i a n c e ) 2 3 4 5 6 7 8 L o g N ( 1 + M e a n ) 1 2 3 4 5 6 7Variance
mean
Overdispersion =
≈ Log(overdispersion)
Trash count
( C i r a d l a b o r a t o r y ) L o g N ( 1 + V a r i a n c e ) 1 2 3 4 5 6 L o g N ( 1 + M e a n ) 1 2 3 4• Variability of some defects measurements
on yarn and fiber
• Known probability distributions as
theoretical landmarks
• Some practical recommandations to
evaluate precision + discussion
Landmark probability distributions
• Independently located defects in a homogeneous material
Poisson distribution
σ² = µ
• Patchy located defects in a homogeneous material
Neyman type A distribution
σ² = µ(1+φ)
• Independantly located defects in an heterogeneous material :
density varies randomly : compound distribution
Log-normal density :
Poisson-lognormal distribution σ² = µ ø
