[R] Hoaglin Outlier Method

From: <khobson_at_fd9ns01.okladot.state.ok.us>
Date: Sat 23 Apr 2005 - 01:23:09 EST

I am a new user of R so please bear with me. I have reviewed some R books, FAQs and such but the volume of material is great. I am in the process of porting my current SAS and SVS Script code to Lotus Approach, R and WordPerfect.

My question is, can you help me determine the best R method to implement the Hoaglin Outlier Method? It is used in the Appendix A and B of the fo llowing link. http://trb.org/publications/nchrp/nchrp_w71.pdf

The sample data from Appendix A for determining outliers in R: T314Data <-
structure(list(Lab = as.integer(c(1:60)), X = c(4.89, 3.82, 2.57, 2.3,

2.034, 2, 1.97, 1.85,
1.85, 1.85, 1.84, 1.82, 1.82, 1.77, 1.76, 1.67, 1.66, 1.63, 1.62,
1.62, 1.55, 1.54, 1.54, 1.53, 1.53, 1.44, 1.428, 1.42, 1.39,
1.36, 1.35, 1.31, 1.28, 1.24, 1.24, 1.23, 1.22, 1.21, 1.19, 1.18,
1.18, 1.18, 1.17, 1.16, 1.13, 1.13, 1.099, 1.09, 1.09, 1.08,
1.07, 1.05, 0.98, 0.97, 0.84, 0.808, 0.69, 0.63, 0.6, 0.5), Y = c(5.28,
3.82, 2.41, 2.32, 2.211, 1.46, 2.24, 1.91, 1.78, 1.63, 1.81,
1.92, 1.2, 1.67, 1.28, 1.59, 1.45, 2.06, 1.91, 1.19, 1.26, 1.79,
1.39, 1.48, 0.72, 1.29, 1.517, 1.71, 1.12, 1.38, 0.93, 1.36,
1.2, 1.23, 0.71, 1.29, 1.26, 1.48, 1.26, 1.33, 1.21, 1.04, 1.57,
1.42, 1.08, 1.04, 1.33, 1.33, 1.2, 1.05, 1.24, 0.91, 0.99, 1.06,
1.27, 0.702, 0.77, 0.58, 1, 0.38)), .Names = c("Lab", "X", "Y"
), class = "data.frame", row.names = c("1", "2", "3", "4", "5",
"6", "7", "8", "9", "10", "11", "12", "13", "14", "15", "16",
"17", "18", "19", "20", "21", "22", "23", "24", "25", "26", "27",
"28", "29", "30", "31", "32", "33", "34", "35", "36", "37", "38",
"39", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49",
"50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "60"
))

>From this point on, I could use your advise. There are several other methods for determining outliers in R. I'd rather not re-invent the wheel or use a brute strength and force method if there is a better way in R.

Our usual method for determining outliers is a student's T test as in ASTM E 178 or when the standard deviation for a lab is 3 or more. We normally have 120 labs to evaluate for outliers similar what is shown in T312Data. On occasion, I have used the Wilk-Shapiro W statistic in SAS. A point in the right direction or an R code example would help greatly. After I trim the outliers, I will need to show which labs were eliminated but that should be fairly trivial.

The reference in Appendix A is:
Hoaglin, D. C., Iglewicz, B., Tukey, J. W., “Performance of Some Resistant Rules for Outlier Labeling,” Journal
of the American Statistical Association, Vol. 81, No. 396 (Dec., 1986), pp. 991-999.

The ASTM E 178 reference is:
Shapiro, S. S., and Wilk, M. B., “An Analysis of Variance Test for Non-Normality (Complete Samples),” Biometrika, BIOKA, Vol 52, 1965, pp. 591–611.

Kenneth Ray Hobson, P.E.
Oklahoma DOT - QA & IAS Manager
200 N.E. 21st Street
Oklahoma City, OK 73105-3204
(405) 522-4985, (405) 522-0552 fax



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