Extreme Deviations

Herds with large percentage of their cows on Elite List may have two management systems in their herds:High producersLow producers

Can cause inflated evaluations when high & low producers are in the same management group

Herds with Elite Cows

~300 herds with 5+ cows on elite listDo their descriptive and normality statistics provide any useful characteristics to identify potentially “bimodal” herds?Does their 1st lactation ME milk deviation distribution look “visually suspicious”?

Look suspicious to you?

Data

12 most “important” dairy statesCalculate each cow’s 1st lactation ME milk deviation from herd annual mean ME milk 1997-2001 18194 herds N 10 (per year)

Descriptive statistics, Normality test statisticsSub data sets of herds with 5+ cows on elite list

Statistics (1)

Descriptive statistics:Skewness (SKEW)Kurtosis (KUR)Standard error of the mean (STDMEAN)

Standard deviation / Sum of weights

Statistics (2)

Normality statistics:Normal vs. non-normalKolmogorov statistic (KS)Problems with normality tests:

Very sensitive to herd size (i.e. >30% of CA herds are “not normally” distributed compared to < 3% in PA, WI, MN)

Should not be used as only criteria

Preliminary Results

Herds with +5 cows on elite list, “not normal”, “visually suspicious”, had higher SKEW and STDMEAN than herds that “looked okay”

Herds with +5 cows on elite list, “not-normal”, had higher SKEW, KUR, and KS than herds designated “normal”

All herds, “not-normal”, had higher SKEW and KUR than herds designated “normal”

Identifying Herds

Use normality and descriptive statistics:

KS 0.08 & (KUR 0.8 || SKEW 0.35) & STDMEAN 250

This threshold successfully identifies ALL of the “visually suspicious” herds and ~29% of all herds (5387 out of 18194)If threshold restricted to herds found not normally distributed first (880 out of 18194), it identifies only 235 herds

STDMEAN & KS vs. % on Elite List

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0 100 200 300 400 500 600 700 800

STDM EAN

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0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

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The higher STDMEAN or KS, the larger the %of cows on the Elite List

Adjusting Herd Data

Based on the value of KS and STDMEAN, incrementally adjust heritability (as in heterogeneous variance adjustment)

Result: records from herds with abnormal distributions receive less weight