sca (version 0.9-0)

pitpropC: Pitprops Strength Correlation Data

Description

This correlation matrix was published in Jeffers (1967) and was calculated from 180 observations. The 13 variables were used as explanatory variables in a regression problem which arised from a study on the strength of pitprops cut from home-grown timber.

Usage

data(pitpropC)

Format

Its a correlation matrix of 13 variables which have the following meaning:

[,1]	TOPDIAM
Top diameter of the prop in inches	[,2]
LENGTH	Length of the prop in inches
[,3]	MOIST
Moisture content of the prop, expressed as a percentage of the dry weight	[,4]
TESTSG	Specific gravity of the timber at the time of the test
[,5]	OVENSG
Oven-dry specific gravity of the timber	[,6]
RINGTOP	Number of annual rings at the top of the prop
[,7]	RINGBUT
Number of annual rings at the base of the prop	[,8]
BOWMAX	Maximum bow in inches
[,9]	BOWDIST
Distance of the point of maximum bow from the top of the prop in inches	[,10]
WHORLS	Number of knot whorls
[,11]	CLEAR
Length of clear prop from the top of the prop in inches	[,12]
KNOTS	Average number of knots per whorl

Details

Jeffers (1967) replaced these 13 variables by their first six principal components. As noted by Vines (2000), this is an example where simple structure has proven difficult to detect in the past.

References

Jeffers, J.N.R. (1967) Two case studies in the application of principal components analysis. Appl. Statist. 16, 225--236.

Vines, S.K. (2000) Simple principal components. Appl. Statist. 49, 441--451.

Examples

data(pitpropC)
symnum(pitpropC)