Stone flakes II

Continuing from last week, the aim is now to classify the stone flakes based on their various properties. Three methods are used. LDA is an obvious standard. A classification tree is both simple and visually appealing. Random forest as a complex method, where more complex relations can easily be captured. Surprising with these data is that the classification tree is doing better than random forest with respect to predicting the input data.

Data

This is the same as last week. However, I now opted to make the group labels a bit more short. r2 <- read.table('StoneFlakes.txt',header=TRUE,na.strings='?') r1 <- read.table('annotation.txt',header=TRUE,na.strings='?') r12 <- merge(r1,r2) r12$Group <- factor(r12$group,labels=c('Lower Paleolithic',     'Levallois technique',     'Middle Paleolithic',     'Homo Sapiens')) r12c <- r12[complete.cases(r12),]

LDA

LDA is part of the MASS package. The settings are default. The plot function has been adapted, to retain proper labeling and colors. ld1 <- lda(Group ~ LBI + RTI + WDI + FLA + PSF + FSF + ZDF1 + PROZD,     data=r12c) ld1 Call: lda(Group ~ LBI + RTI + WDI + FLA + PSF + FSF + ZDF1 + PROZD,      data = r12c) Prior probabilities of groups:   Lower Paleolithic Levallois technique  Middle Paleolithic        Homo Sapiens           0.15492958          0.32394366          0.47887324          0.04225352  Group means:                          LBI      RTI      WDI      FLA       PSF       FSF Lower Paleolithic   1.105455 33.82727 2.690000 118.8182 31.881818  8.372727 Levallois technique 1.254348 28.74348 2.768261 121.2609 15.021739 14.900000 Middle Paleolithic  1.195000 25.88235 3.384412 113.9706  9.497059 23.294118 Homo Sapiens        1.453333 22.96333 3.150000 117.0000  7.666667 27.900000                         ZDF1    PROZD Lower Paleolithic   15.86364 57.81818 Levallois technique 30.46087 69.17391 Middle Paleolithic  62.31471 84.23529 Homo Sapiens        56.36667 87.00000 Coefficients of linear discriminants:               LD1           LD2         LD3 LBI    2.63864596 -7.3053369000  4.96921267 RTI    0.03735899  0.0683327644  0.03955854 WDI    0.64616126 -0.3086473881  0.06507385 FLA   -0.04798439 -0.0591106950 -0.05229559 PSF   -0.01917272  0.0515112771  0.10178299 FSF    0.02488002 -0.0001579818  0.07080551 ZDF1   0.02896112  0.0396366883 -0.01625858 PROZD  0.03036974 -0.0079845555  0.04335520 Proportion of trace:    LD1    LD2    LD3  0.7026 0.2585 0.0389  There are eight objects incorrect classified. Out of 71 complete cases, that is 10% wrong. mydf <- data.frame(ID=r12c$ID,     Group=r12c$Group,     predict=predict(ld1)$class) mydf[mydf$Group!=mydf$pred,]     ID               Group             predict 9    c  Middle Paleolithic Levallois technique 10  cl   Lower Paleolithic Levallois technique 37  ms Levallois technique   Lower Paleolithic 38   n  Middle Paleolithic Levallois technique 45 roe  Middle Paleolithic Levallois technique 55  sz Levallois technique  Middle Paleolithic 61  va Levallois technique        Homo Sapiens 68 woe   Lower Paleolithic Levallois technique

LDA Plot

Classification tree

Rpart is my favorite classification tree implementation. The only tuning is setting minsplit to 10, the default of 20 seems a bit large for 79 objects and four categories. The printed output is skipped, since we have the plot. The interpretation is pretty simple. First split on ZDF1, to distinguish old from young (less old?). The young can be split on LBI to Middle paleolithic and homo sapiens. The old by PSF to Levoillas and Lower Paleolithic. A final split between middle and lower paleolithic shows that the differences are not clear cut. There are ten incorrect predicted objects. Note that it is difficult to compare this with LDA, since objects with missing data (e.g. sk misses FLA, PSF, FSF) are predicted with rpart, while they were removed prior to LDA analysis.