Perturb: Tools for Evaluating Collinearity

# Belsley (1991). "Conditioning Diagnostics"
# The Consumption Function (pp. 149-154)
consumption <- read.table(header=TRUE,text="
year	cons	rate	dpi	d_dpi
1947	206.275	2.61083	218.075	-9.375
1948	210.775	2.81667	229.7	11.625
1949	216.5	2.66	230.925	1.225
1950	230.5	2.6225	249.65	18.725
1951	232.825	2.86	255.675	6.025
1952	239.425	2.95583	263.25	7.575
1953	250.775	3.19917	275.475	12.225
1954	255.725	2.90083	278.4	2.925
1955	274.2	3.0525	296.625	18.225
1956	281.4	3.36417	309.35	12.725
1957	288.15	3.885	316.075	6.725
1958	290.05	3.7875	318.8	2.725
1959	307.3	4.38167	333.05	14.25
1960	316.075	4.41	340.325	7.275
1961	322.5	4.35	350.475	10.15
1962	338.425	4.325	367.25	16.775
1963	353.3	4.25917	381.225	13.975
1964	373.725	4.40417	408.1	26.875
1965	397.7	4.49333	434.825	26.725
1966	418.1	5.13	458.875	24.05
1967	430.1	5.50667	477.55	18.675
1968	452.725	6.175	499.05	21.5
1969	469.125	7.02917	513.5	14.45
1970	477.55	8.04	534.75	21.25
1971	496.425	7.38667	555.425	20.675
1972	527.35	7.21333	580.45	25.025
1973	552.075	7.44083	619.5	39.05
1974	539.45	8.56583	602.875	-16.625
")
consumption <- data.frame(consumption)