The PRINCOMP Procedure
Output Data Sets
OUT= Data Set
The OUT= data set contains all the variables in the original data set plus new variables containing the principal component
scores. The N= option determines the number of new variables. The names of the new variables are formed by concatenating the
value given by the PREFIX= option (or Prin if PREFIX= is omitted) and the numbers 1, 2, 3, and so on. The new variables have mean 0 and variance equal to the corresponding
eigenvalue, unless you specify the STANDARD option to standardize the scores to unit variance. Also, if you specify the COV
option, the procedure computes the principal component scores from the corrected or the uncorrected (if the NOINT option is
specified) variables rather than the standardized variables.
If you use a PARTIAL statement, the OUT= data set also contains the residuals from predicting the VAR variables from the PARTIAL variables.
An OUT= data set cannot be created if the DATA= data set is TYPE=ACE, TYPE=CORR, TYPE=COV, TYPE=EST, TYPE=FACTOR, TYPE=SSCP, TYPE=UCORR, or TYPE=UCOV.
OUTSTAT= Data Set
The OUTSTAT= data set is similar to the TYPE=CORR data set produced by the CORR procedure. The following table relates the TYPE= value for the OUTSTAT= data set to the options specified in the PROC PRINCOMP statement.
|
Options |
TYPE= |
|
|---|---|---|
|
(default) |
CORR |
|
|
COV |
COV |
|
|
NOINT |
UCORR |
|
|
COV NOINT |
UCOV |
|
Note that the default (neither the COV nor NOINT option) produces a TYPE=CORR data set.
The new data set contains the following variables:
-
the BY variables, if any
-
two new variables,
_TYPE_and_NAME_, both character variables -
the variables analyzed (that is, those in the VAR statement); or, if there is no VAR statement, all numeric variables not listed in any other statement; or, if there is a PARTIAL statement, the residual variables as described under the OUT= data set
Each observation in the new data set contains some type of statistic as indicated by the _TYPE_ variable. The values of the _TYPE_ variable are as follows:
- MEAN
-
mean of each variable. If you specify the PARTIAL statement, this observation is omitted.
- STD
-
standard deviations. If you specify the COV option, this observation is omitted, so the SCORE procedure does not standardize the variables before computing scores. If you use the PARTIAL statement, the standard deviation of a variable is computed as its root mean squared error as predicted from the PARTIAL variables.
- USTD
-
uncorrected standard deviations. When you specify the NOINT option in the PROC PRINCOMP statement, the OUTSTAT= data set contains standard deviations not corrected for the mean. However, if you also specify the COV option in the PROC PRINCOMP statement, this observation is omitted.
- N
-
number of observations on which the analysis is based. This value is the same for each variable. If you specify the PARTIAL statement and the value of the VARDEF= option is DF or unspecified, then the number of observations is decremented by the degrees of freedom for the PARTIAL variables.
- SUMWGT
-
the sum of the weights of the observations. This value is the same for each variable. If you specify the PARTIAL statement and VARDEF=WDF, then the sum of the weights is decremented by the degrees of freedom for the PARTIAL variables. This observation is output only if the value is different from that in the observation with
_TYPE_=‘N’. - CORR
-
correlations between each variable and the variable specified by the
_NAME_variable. The number of observations with_TYPE_=‘CORR’ is equal to the number of variables being analyzed. If you specify the COV option, no_TYPE_=‘CORR’ observations are produced. If you use the PARTIAL statement, the partial correlations, not the raw correlations, are output. - UCORR
-
uncorrected correlation matrix. When you specify the NOINT option without the COV option in the PROC PRINCOMP statement, the OUTSTAT= data set contains a matrix of correlations not corrected for the means. However, if you also specify the COV option in the PROC PRINCOMP statement, this observation is omitted.
- COV
-
covariances between each variable and the variable specified by the
_NAME_variable._TYPE_=‘COV’ observations are produced only if you specify the COV option. If you use the PARTIAL statement, the partial covariances, not the raw covariances, are output. - UCOV
-
uncorrected covariance matrix. When you specify the NOINT and COV options in the PROC PRINCOMP statement, the OUTSTAT= data set contains a matrix of covariances not corrected for the means.
- EIGENVAL
-
eigenvalues. If the N= option requested fewer than the maximum number of principal components, only the specified number of eigenvalues are produced, with missing values filling out the observation.
- SCORE
-
eigenvectors. The
_NAME_variable contains the name of the corresponding principal component as constructed from the PREFIX= option. The number of observations with_TYPE_=‘SCORE’ equals the number of principal components computed. The eigenvectors have unit length unless you specify the STD option, in which case the unit-length eigenvectors are divided by the square roots of the eigenvalues to produce scores with unit standard deviations.To obtain the principal component scores, if the COV option is not specified, these coefficients should be multiplied by the standardized data. With the COV option, these coefficients should be multiplied by the centered data. Means obtained from the observation with
_TYPE_=’MEAN’ and standard deviations obtained from the observation with_TYPE_=’STD’ should be used for centering and standardizing the data. - USCORE
-
scoring coefficients to be applied without subtracting the mean from the raw variables.
_TYPE_=‘USCORE’ observations are produced when you specify the NOINT option in the PROC PRINCOMP statement.To obtain the principal component scores, these coefficients should be multiplied by the data that are standardized by the uncorrected standard deviations obtained from the observation with
_TYPE_=’USTD’. - RSQUARED
-
R squares for each VAR variable as predicted by the PARTIAL variables
- B
-
regression coefficients for each VAR variable as predicted by the PARTIAL variables. This observation is produced only if you specify the COV option.
- STB
-
standardized regression coefficients for each VAR variable as predicted by the PARTIAL variables. If you specify the COV option, this observation is omitted.
The data set can be used with the SCORE procedure to compute principal component scores, or it can be used as input to the FACTOR procedure specifying METHOD=SCORE to rotate the components. If you use the PARTIAL statement, the scoring coefficients should be applied to the residuals, not the original variables.