liu: Liu Regression and Estimator

Description Usage Arguments Details Value Note Author(s) References See Also Examples

Description

Fits a linear Liu regression model after scaling regressors and returns an object of class "liu" (by calling liuest function), designed to be used in plotting method, testing of Liu coefficients and for computation of different Liu related statistics. The Liu biasing parameter d can be a scalar or a vector. This new biased estimator was first proposed by Liu (1993) <doi:10.1080/03610929308831027>.

Usage

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liu(formula, data, d = 1, scaling=c("centered", "sc", "scaled"), ...)
liuest(formula, data, d=1, scaling=c("centered", "sc", "scaled"), ...)
## Default S3 method:
liu(formula, data, d = 1, scaling=c("centered", "sc", "scaled"), ...)
## S3 method for class 'liu'
coef(object, ...)
## S3 method for class 'liu'
print(x, digits = max(5,getOption("digits") - 5), ...)
## S3 method for class 'liu'
fitted(object, ...)

Arguments

formula

Standard R formula expression, that is, a symbolic representation of the model to be fitted and has form response~predictors. For further details, see formula.

data

An optional data frame containing the variables in the model. If not found in data, the variables are taken from environment(formula), typically the environment from which liu or liuest is called.

d

Liu biasing parameter (may be a vector).

scaling

The method to be used to scale the predictors. The scaling option "sc" scales the predictors to correlation form, such that the correlation matrix has unit diagonal elements. "scaled" option standardizes the predictors to have zero mean and unit variance. "centered" option centers the predictors.

object

A liu object, typically generated by a call to liu for fitted.liu, predict.liu, vcov.liu, residuals.liu, infocr.liu, coef.liu, summary.liu and press.liu functions.

x

An object of class liu (for the hatl.liu, lstats.liu, dest.liu, summary.liu, print.liu, print.summary.liu, print.dest, print.lstats, and plot.liu, plot.biasliu and plot.infoliu.

digits

Minimum number of significant digits to be used.

...

Additional arguments to be passed to or from other methods.

Details

liu or liuest function fits in Liu regression after scaling the regressors and centering the response. The liu is default a function that calls liuest for computation of Liu coefficients and returns an object of class "liu" designed to be used in plotting method, testing of Liu coefficients and for computation of different Liu related statistics. If intercept is present in the model, its coefficient is not penalized. However, intercept is estimated from the relation y=\overline{y}-β \overline{X}. print.liu tries to be smart about formatting of Liu coefficients.

Value

liu function returns an object of class "liu" after calling list of named objects from liuest function:

coef

A named vector of fitted coefficients.

call

The matched call.

Inter

Was an intercept included?

scaling

The scaling method used.

mf

Actual data used.

y

The centered response variable.

xs

The scaled matrix of predictors.

xm

The vector of means of the predictors.

terms

The terms object used.

xscale

Square root of sum of squared deviation from mean regarding the scaling option used in liu or liuest function as argument.

lfit

The fitted value of Liu regression for given biasing parameter d.

d

The Liu regression biasing parameter d which can be scalar or a vector.

Note

The function at the current form cannot handle missing values. The user has to take prior action with missing values before using this function.

Author(s)

Muhammad Imdad Ullah, Muhammad Aslam

References

Akdeniz, F. and Kaciranlar, S. (1995). On the Almost Unbiased Generalized Liu Estimators and Unbiased Estimation of the Bias and MSE. Communications in Statistics-Theory and Methods, 24, 1789–1897. http://doi.org/10.1080/03610929508831585.

Imdad, M. U. (2017). Addressing Linear Regression Models with Correlated Regressors: Some Package Development in R (Doctoral Thesis, Department of Statistics, Bahauddin Zakariya University, Multan, Pakistan).

Imdadullah, M., Aslam, M., and Altaf, S. (2017). liureg: A comprehensive R Package for the Liu Estimation of Linear Regression Model with Collinear Regressors. The R Journal, 9 (2), 232–247.

Liu, K. (1993). A new Class of Biased Estimate in Linear Regression. Journal of Statistical Planning and Inference, 141, 189–196. http://doi.org/10.1080/03610929308831027.

See Also

Liu model fitting liu, Liu residuals residuals.liu, Liu PRESS press.liu, Testing of Liu Coefficients summary.liu

Examples

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data(Hald)
mod<-liu(y~., data = as.data.frame(Hald), d = seq(0, 0.1, 0.01), scaling = "centered")
## Scaled Coefficients
mod$coef

## Re-Scaled Coefficients
coef(mod)

## Liu fitted values
fitted(mod)

## Liu predited values
predict(mod)

## Liu Residuals
residuals(mod)

## Liu trace
plot(mod)

## Liu Var-Cov matrix
vcov(mod)

## Liu biasing parameters by researchers
dest(mod)

## Liu related statistics
lstats(mod)

## list of objects from liuest function
liuest(y~., data = as.data.frame(Hald), d = seq(0, 0.1, 0.01), scaling = "centered")

Example output

           d=0      d=0.01      d=0.02      d=0.03      d=0.04      d=0.05
X1  1.41348287  1.41485907  1.41623526  1.41761146  1.41898766  1.42036386
X2  0.38189878  0.38318147  0.38446416  0.38574685  0.38702953  0.38831222
X3 -0.03582438 -0.03444704 -0.03306971 -0.03169237 -0.03031503 -0.02893769
X4 -0.27031652 -0.26905396 -0.26779141 -0.26652885 -0.26526630 -0.26400374
        d=0.06      d=0.07      d=0.08      d=0.09      d=0.1
X1  1.42174006  1.42311625  1.42449245  1.42586865  1.4272448
X2  0.38959491  0.39087760  0.39216029  0.39344297  0.3947257
X3 -0.02756035 -0.02618302 -0.02480568 -0.02342834 -0.0220510
X4 -0.26274119 -0.26147863 -0.26021608 -0.25895352 -0.2576910
       Intercept       X1        X2          X3         X4
d=0     75.01755 1.413483 0.3818988 -0.03582438 -0.2703165
d=0.01  74.89142 1.414859 0.3831815 -0.03444704 -0.2690540
d=0.02  74.76530 1.416235 0.3844642 -0.03306971 -0.2677914
d=0.03  74.63918 1.417611 0.3857468 -0.03169237 -0.2665289
d=0.04  74.51306 1.418988 0.3870295 -0.03031503 -0.2652663
d=0.05  74.38694 1.420364 0.3883122 -0.02893769 -0.2640037
d=0.06  74.26082 1.421740 0.3895949 -0.02756035 -0.2627412
d=0.07  74.13469 1.423116 0.3908776 -0.02618302 -0.2614786
d=0.08  74.00857 1.424492 0.3921603 -0.02480568 -0.2602161
d=0.09  73.88245 1.425869 0.3934430 -0.02342834 -0.2589535
d=0.1   73.75633 1.427245 0.3947257 -0.02205100 -0.2576910
         d=0    d=0.01    d=0.02    d=0.03    d=0.04    d=0.05    d=0.06
1  -17.01572 -17.01484 -17.01396 -17.01308 -17.01220 -17.01133 -17.01045
2  -22.51081 -22.51204 -22.51328 -22.51451 -22.51575 -22.51698 -22.51822
3   10.83619  10.83330  10.83042  10.82754  10.82465  10.82177  10.81889
4   -6.00983  -6.01069  -6.01155  -6.01241  -6.01327  -6.01414  -6.01500
5    0.21219   0.21233   0.21247   0.21261   0.21275   0.21289   0.21303
6    9.87783   9.87757   9.87730   9.87704   9.87678   9.87651   9.87625
7    8.71882   8.71889   8.71895   8.71902   8.71909   8.71916   8.71922
8  -19.83525 -19.83438 -19.83351 -19.83263 -19.83176 -19.83089 -19.83002
9   -3.54783  -3.54937  -3.55091  -3.55244  -3.55398  -3.55551  -3.55705
10  20.05532  20.05673  20.05813  20.05953  20.06093  20.06233  20.06373
11 -13.73082 -13.72965 -13.72848 -13.72732 -13.72615 -13.72498 -13.72381
12  16.78188  16.78310  16.78432  16.78554  16.78676  16.78799  16.78921
13  16.16802  16.16905  16.17009  16.17112  16.17215  16.17318  16.17422
      d=0.07    d=0.08    d=0.09     d=0.1
1  -17.00957 -17.00869 -17.00781 -17.00693
2  -22.51945 -22.52069 -22.52192 -22.52316
3   10.81600  10.81312  10.81024  10.80735
4   -6.01586  -6.01672  -6.01758  -6.01844
5    0.21317   0.21331   0.21345   0.21359
6    9.87599   9.87572   9.87546   9.87520
7    8.71929   8.71936   8.71943   8.71949
8  -19.82915 -19.82828 -19.82740 -19.82653
9   -3.55858  -3.56012  -3.56166  -3.56319
10  20.06513  20.06653  20.06793  20.06933
11 -13.72265 -13.72148 -13.72031 -13.71914
12  16.79043  16.79165  16.79287  16.79409
13  16.17525  16.17628  16.17731  16.17835
         d=0    d=0.01    d=0.02    d=0.03    d=0.04    d=0.05    d=0.06
1   78.40736  78.40824  78.40911  78.40999  78.41087  78.41175  78.41263
2   72.91227  72.91103  72.90980  72.90856  72.90733  72.90610  72.90486
3  106.25926 106.25638 106.25350 106.25061 106.24773 106.24485 106.24196
4   89.41325  89.41239  89.41153  89.41066  89.40980  89.40894  89.40808
5   95.63527  95.63541  95.63555  95.63569  95.63583  95.63597  95.63611
6  105.30091 105.30064 105.30038 105.30012 105.29985 105.29959 105.29933
7  104.14189 104.14196 104.14203 104.14210 104.14217 104.14223 104.14230
8   75.58783  75.58870  75.58957  75.59044  75.59131  75.59219  75.59306
9   91.87524  91.87371  91.87217  91.87064  91.86910  91.86756  91.86603
10 115.47840 115.47980 115.48120 115.48260 115.48400 115.48540 115.48680
11  81.69226  81.69343  81.69459  81.69576  81.69693  81.69810  81.69926
12 112.20496 112.20618 112.20740 112.20862 112.20984 112.21106 112.21228
13 111.59110 111.59213 111.59316 111.59420 111.59523 111.59626 111.59729
      d=0.07    d=0.08    d=0.09     d=0.1
1   78.41351  78.41439  78.41527  78.41615
2   72.90363  72.90239  72.90116  72.89992
3  106.23908 106.23620 106.23331 106.23043
4   89.40722  89.40636  89.40549  89.40463
5   95.63625  95.63639  95.63653  95.63667
6  105.29906 105.29880 105.29854 105.29827
7  104.14237 104.14244 104.14250 104.14257
8   75.59393  75.59480  75.59567  75.59654
9   91.86449  91.86296  91.86142  91.85988
10 115.48821 115.48961 115.49101 115.49241
11  81.70043  81.70160  81.70277  81.70393
12 112.21350 112.21472 112.21594 112.21716
13 111.59832 111.59936 111.60039 111.60142
           d=0      d=0.01      d=0.02      d=0.03      d=0.04      d=0.05
1   0.09264302  0.09176419  0.09088537  0.09000654  0.08912771  0.08824889
2   1.38773119  1.38896589  1.39020058  1.39143528  1.39266997  1.39390467
3  -1.95926381 -1.95638055 -1.95349729 -1.95061403 -1.94773076 -1.94484750
4  -1.81324831 -1.81238683 -1.81152535 -1.81066387 -1.80980239 -1.80894091
5   0.26472874  0.26458900  0.26444927  0.26430954  0.26416981  0.26403008
6   3.89909238  3.89935589  3.89961939  3.89988289  3.90014640  3.90040990
7  -1.44189439 -1.44196214 -1.44202989 -1.44209763 -1.44216538 -1.44223313
8  -3.08782783 -3.08869944 -3.08957104 -3.09044265 -3.09131426 -3.09218586
9   1.22475642  1.22629235  1.22782828  1.22936421  1.23090014  1.23243607
10  0.42159811  0.42019761  0.41879711  0.41739661  0.41599611  0.41459561
11  2.10774235  2.10657476  2.10540717  2.10423958  2.10307200  2.10190441
12  1.09504061  1.09382010  1.09259958  1.09137906  1.09015855  1.08893803
13 -2.19109847 -2.19213082 -2.19316318 -2.19419553 -2.19522789 -2.19626025
        d=0.06      d=0.07      d=0.08      d=0.09       d=0.1
1   0.08737006  0.08649124  0.08561241  0.08473358  0.08385476
2   1.39513936  1.39637406  1.39760875  1.39884345  1.40007814
3  -1.94196424 -1.93908097 -1.93619771 -1.93331445 -1.93043119
4  -1.80807943 -1.80721795 -1.80635647 -1.80549499 -1.80463351
5   0.26389034  0.26375061  0.26361088  0.26347115  0.26333142
6   3.90067340  3.90093690  3.90120041  3.90146391  3.90172741
7  -1.44230088 -1.44236862 -1.44243637 -1.44250412 -1.44257186
8  -3.09305747 -3.09392908 -3.09480068 -3.09567229 -3.09654390
9   1.23397200  1.23550793  1.23704386  1.23857979  1.24011573
10  0.41319511  0.41179460  0.41039410  0.40899360  0.40759310
11  2.10073682  2.09956923  2.09840165  2.09723406  2.09606647
12  1.08771752  1.08649700  1.08527649  1.08405597  1.08283545
13 -2.19729260 -2.19832496 -2.19935732 -2.20038967 -2.20142203
$`d=0`
          X1        X2        X3        X4
X1 0.2753729 0.2439503 0.2710395 0.2411783
X2 0.2439503 0.2589659 0.2515646 0.2522639
X3 0.2710395 0.2515646 0.2805669 0.2475798
X4 0.2411783 0.2522639 0.2475798 0.2475877

$`d=0.01`
          X1        X2        X3        X4
X1 0.2772320 0.2457575 0.2729319 0.2429533
X2 0.2457575 0.2607311 0.2534059 0.2539971
X3 0.2729319 0.2534059 0.2824945 0.2493882
X4 0.2429533 0.2539971 0.2493882 0.2492897

$`d=0.02`
          X1        X2        X3        X4
X1 0.2790977 0.2475710 0.2748310 0.2447345
X2 0.2475710 0.2625025 0.2552537 0.2557365
X3 0.2748310 0.2552537 0.2844289 0.2512029
X4 0.2447345 0.2557365 0.2512029 0.2509977

$`d=0.03`
          X1        X2        X3        X4
X1 0.2809698 0.2493909 0.2767367 0.2465221
X2 0.2493909 0.2642801 0.2571079 0.2574819
X3 0.2767367 0.2571079 0.2863701 0.2530241
X4 0.2465221 0.2574819 0.2530241 0.2527116

$`d=0.04`
          X1        X2        X3        X4
X1 0.2828485 0.2512171 0.2786490 0.2483158
X2 0.2512171 0.2660639 0.2589687 0.2592333
X3 0.2786490 0.2589687 0.2883180 0.2548516
X4 0.2483158 0.2592333 0.2548516 0.2544315

$`d=0.05`
          X1        X2        X3        X4
X1 0.2847337 0.2530497 0.2805679 0.2501158
X2 0.2530497 0.2678539 0.2608359 0.2609909
X3 0.2805679 0.2608359 0.2902726 0.2566854
X4 0.2501158 0.2609909 0.2566854 0.2561573

$`d=0.06`
          X1        X2        X3        X4
X1 0.2866254 0.2548886 0.2824935 0.2519220
X2 0.2548886 0.2696500 0.2627096 0.2627545
X3 0.2824935 0.2627096 0.2922340 0.2585256
X4 0.2519220 0.2627545 0.2585256 0.2578892

$`d=0.07`
          X1        X2        X3        X4
X1 0.2885236 0.2567339 0.2844257 0.2537345
X2 0.2567339 0.2714524 0.2645897 0.2645242
X3 0.2844257 0.2645897 0.2942022 0.2603722
X4 0.2537345 0.2645242 0.2603722 0.2596270

$`d=0.08`
          X1        X2        X3        X4
X1 0.2904283 0.2585856 0.2863646 0.2555532
X2 0.2585856 0.2732609 0.2664763 0.2663000
X3 0.2863646 0.2664763 0.2961771 0.2622251
X4 0.2555532 0.2663000 0.2622251 0.2613707

$`d=0.09`
          X1        X2        X3        X4
X1 0.2923395 0.2604436 0.2883100 0.2573781
X2 0.2604436 0.2750756 0.2683694 0.2680818
X3 0.2883100 0.2683694 0.2981587 0.2640844
X4 0.2573781 0.2680818 0.2640844 0.2631204

$`d=0.1`
          X1        X2        X3        X4
X1 0.2942571 0.2623079 0.2902621 0.2592093
X2 0.2623079 0.2768964 0.2702690 0.2698697
X3 0.2902621 0.2702690 0.3001471 0.2659500
X4 0.2592093 0.2698697 0.2659500 0.2648760

Liu biasing parameter d
           d values
dmm        -5.91524
dcl        -5.97369
dopt       -1.47218
dILE       -0.83461
min GCV at  0.00000

Liu Regression Statistics:

          EDF Sigma2     CL    VAR Bias^2    MSE        F     R2 adj-R2
d=0    9.0677 5.3010 5.5315 1.0625 0.0703 1.1328 125.8194 0.9823 0.9735
d=0.01 9.0663 5.3014 5.5355 1.0697 0.0689 1.1387 125.8114 0.9823 0.9735
d=0.02 9.0650 5.3017 5.5395 1.0770 0.0675 1.1445 125.8034 0.9823 0.9735
d=0.03 9.0637 5.3021 5.5436 1.0843 0.0661 1.1505 125.7956 0.9823 0.9735
d=0.04 9.0624 5.3024 5.5476 1.0917 0.0648 1.1565 125.7878 0.9823 0.9735
d=0.05 9.0611 5.3027 5.5517 1.0990 0.0634 1.1625 125.7801 0.9823 0.9735
d=0.06 9.0598 5.3030 5.5558 1.1064 0.0621 1.1685 125.7724 0.9823 0.9735
d=0.07 9.0585 5.3033 5.5599 1.1138 0.0608 1.1746 125.7649 0.9823 0.9735
d=0.08 9.0573 5.3037 5.5640 1.1212 0.0595 1.1807 125.7574 0.9823 0.9735
d=0.09 9.0560 5.3040 5.5681 1.1287 0.0582 1.1869 125.7500 0.9823 0.9735
d=0.1  9.0548 5.3043 5.5722 1.1362 0.0569 1.1931 125.7427 0.9823 0.9735

minimum MSE occurred at d = 0 
$coef
           d=0      d=0.01      d=0.02      d=0.03      d=0.04      d=0.05
X1  1.41348287  1.41485907  1.41623526  1.41761146  1.41898766  1.42036386
X2  0.38189878  0.38318147  0.38446416  0.38574685  0.38702953  0.38831222
X3 -0.03582438 -0.03444704 -0.03306971 -0.03169237 -0.03031503 -0.02893769
X4 -0.27031652 -0.26905396 -0.26779141 -0.26652885 -0.26526630 -0.26400374
        d=0.06      d=0.07      d=0.08      d=0.09      d=0.1
X1  1.42174006  1.42311625  1.42449245  1.42586865  1.4272448
X2  0.38959491  0.39087760  0.39216029  0.39344297  0.3947257
X3 -0.02756035 -0.02618302 -0.02480568 -0.02342834 -0.0220510
X4 -0.26274119 -0.26147863 -0.26021608 -0.25895352 -0.2576910

$xscale
[1] 1 1 1 1

$xs
           X1         X2        X3  X4
1  -0.4615385 -22.153846 -5.769231  30
2  -6.4615385 -19.153846  3.230769  22
3   3.5384615   7.846154 -3.769231 -10
4   3.5384615 -17.153846 -3.769231  17
5  -0.4615385   3.846154 -5.769231   3
6   3.5384615   6.846154 -2.769231  -8
7  -4.4615385  22.846154  5.230769 -24
8  -6.4615385 -17.153846 10.230769  14
9  -5.4615385   5.846154  6.230769  -8
10 13.5384615  -1.153846 -7.769231  -4
11 -6.4615385  -8.153846 11.230769   4
12  3.5384615  17.846154 -2.769231 -18
13  2.5384615  19.846154 -3.769231 -18

$Inter
[1] 1

$xm
       X1        X2        X3        X4 
 7.461538 48.153846 11.769231 30.000000 

$y
          1           2           3           4           5           6 
-16.9230769 -21.1230769   8.8769231  -7.8230769   0.4769231  13.7769231 
          7           8           9          10          11          12 
  7.2769231 -22.9230769  -2.3230769  20.4769231 -11.6230769  17.8769231 
         13 
 13.9769231 

$scaling
[1] "centered"

$call
liuest(formula = y ~ ., data = as.data.frame(Hald), d = seq(0, 
    0.1, 0.01), scaling = "centered")

$d
 [1] 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

$lfit
              d=0      d=0.01      d=0.02      d=0.03      d=0.04     d=0.05
 [1,] -17.0157199 -17.0148411 -17.0139623 -17.0130835 -17.0122046 -17.011326
 [2,] -22.5108081 -22.5120428 -22.5132775 -22.5145122 -22.5157469 -22.516982
 [3,]  10.8361869  10.8333036  10.8304204  10.8275371  10.8246538  10.821771
 [4,]  -6.0098286  -6.0106901  -6.0115516  -6.0124131  -6.0132745  -6.014136
 [5,]   0.2121943   0.2123341   0.2124738   0.2126135   0.2127533   0.212893
 [6,]   9.8778307   9.8775672   9.8773037   9.8770402   9.8767767   9.876513
 [7,]   8.7188175   8.7188852   8.7189530   8.7190207   8.7190885   8.719156
 [8,] -19.8352491 -19.8343775 -19.8335059 -19.8326343 -19.8317627 -19.830891
 [9,]  -3.5478333  -3.5493693  -3.5509052  -3.5524411  -3.5539771  -3.555513
[10,]  20.0553250  20.0567255  20.0581260  20.0595265  20.0609270  20.062327
[11,] -13.7308193 -13.7296517 -13.7284841 -13.7273165 -13.7261489 -13.724981
[12,]  16.7818825  16.7831030  16.7843235  16.7855440  16.7867645  16.787985
[13,]  16.1680215  16.1690539  16.1700863  16.1711186  16.1721510  16.173183
           d=0.06      d=0.07      d=0.08      d=0.09       d=0.1
 [1,] -17.0104470 -17.0095682 -17.0086893 -17.0078105 -17.0069317
 [2,] -22.5182163 -22.5194510 -22.5206857 -22.5219204 -22.5231551
 [3,]  10.8188873  10.8160041  10.8131208  10.8102375  10.8073543
 [4,]  -6.0149975  -6.0158590  -6.0167205  -6.0175819  -6.0184434
 [5,]   0.2130327   0.2131725   0.2133122   0.2134519   0.2135917
 [6,]   9.8762497   9.8759862   9.8757227   9.8754592   9.8751957
 [7,]   8.7192240   8.7192917   8.7193594   8.7194272   8.7194949
 [8,] -19.8300195 -19.8291478 -19.8282762 -19.8274046 -19.8265330
 [9,]  -3.5570489  -3.5585849  -3.5601208  -3.5616567  -3.5631926
[10,]  20.0637280  20.0651285  20.0665290  20.0679295  20.0693300
[11,] -13.7238137 -13.7226462 -13.7214786 -13.7203110 -13.7191434
[12,]  16.7892056  16.7904261  16.7916466  16.7928671  16.7940876
[13,]  16.1742157  16.1752480  16.1762804  16.1773127  16.1783451

$mf
       y X1 X2 X3 X4
1   78.5  7 26  6 60
2   74.3  1 29 15 52
3  104.3 11 56  8 20
4   87.6 11 31  8 47
5   95.9  7 52  6 33
6  109.2 11 55  9 22
7  102.7  3 71 17  6
8   72.5  1 31 22 44
9   93.1  2 54 18 22
10 115.9 21 47  4 26
11  83.8  1 40 23 34
12 113.3 11 66  9 12
13 109.4 10 68  8 12

$terms
y ~ X1 + X2 + X3 + X4
attr(,"variables")
list(y, X1, X2, X3, X4)
attr(,"factors")
   X1 X2 X3 X4
y   0  0  0  0
X1  1  0  0  0
X2  0  1  0  0
X3  0  0  1  0
X4  0  0  0  1
attr(,"term.labels")
[1] "X1" "X2" "X3" "X4"
attr(,"order")
[1] 1 1 1 1
attr(,"intercept")
[1] 1
attr(,"response")
[1] 1
attr(,".Environment")
<environment: R_GlobalEnv>
attr(,"predvars")
list(y, X1, X2, X3, X4)
attr(,"dataClasses")
        y        X1        X2        X3        X4 
"numeric" "numeric" "numeric" "numeric" "numeric" 

liureg documentation built on May 2, 2019, 8:34 a.m.