Before and after running ACE Models, it is important to examine the characteristics of the different groups. When the ACE is estimated with an SEM using multiple groups, it is even even more important. Groups may contain too few subjects to have a well-behaved covariance matrix.

If a group's covariance matrix is not Positive Definite (or it's misbehaving in some other way), it's typically recommended to exclude that group from the SEM.

1 | ```
RGroupSummary(ds, oName_S1, oName_S2, rName, determinantThreshold=1e-5)
``` |

`ds` |
The |

`oName_S1` |
The name of the outcome variable corresponding to the first subject in the pair. |

`oName_S2` |
The name of the outcome variable corresponding to the first subject in the pair. |

`rName` |
The name of the variable specifying the pair's |

`determinantThreshold` |
The minimum value the covariance matrix's determinant (for the group) should exceed to be considered Positive Definite. |

This function isn't specific to an ACE model and groups defined by `R`

. It could be applied to any multiple-group SEM with two manifest/outcome variables. In the future, we may generalize it beyond two manifest variables.

To get summary stats for the entire sample, create a dummy indicator variable that assigns everyone to the same group. See the second example below.

The default determinantThreshold value is nonzero, in order to forgive slight numerical inaccuracies caused by fixed-precision arithmetic.

A `data.frame`

with one row per group. The `data.frame`

contains the following variables:

` R ` |
The group's |

` Included ` |
Indicates if the group should be included in a multiple-group SEM. |

` PairCount ` |
The number of pairs in the group with |

` O1Mean ` |
The mean (of the outcome variable) among the group's first members, excluding the missing values. |

` O2Mean ` |
The mean (of the outcome variable) among the group's second members, excluding the missing values. |

` O1Variance ` |
The variance (of the outcome variable) among the group's first members. |

` O2Variance ` |
The variance (of the outcome variable) among the group's second members. |

` O1O2Covariance ` |
The covariance (of the outcome variable) across the group's first and second members. |

` Correlation ` |
The correlation (of the outcome variable) across the group's first and second members. |

` Determinant ` |
The determinant of the group's covariance matrix. |

` PosDefinite ` |
Indicates if the group's covariance matrix is positive definite. |

Will Beasley and David Bard

Please see Neale & Maes for more information about SEM with multiple groups.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | ```
library(NlsyLinks) #Load the package into the current R session.
dsLinks <- Links79PairExpanded #Load the dataset from the NlsyLinks package.
dsLinks <- dsLinks[dsLinks$RelationshipPath=='Gen2Siblings', ]
oName_S1 <- "MathStandardized_S1" #Stands for Outcome1
oName_S2 <- "MathStandardized_S2" #Stands for Outcome2
dsGroupSummary <- RGroupSummary(dsLinks, oName_S1, oName_S2)
dsGroupSummary
#Should return:
# R Included PairCount O1Mean O2Mean O1Variance O2Variance O1O2Covariance Correlation
#1 0.250 TRUE 2718 94.6439 95.5990 169.650 207.842 41.0783 0.218761
#2 0.375 TRUE 139 92.6043 93.1655 172.531 187.081 40.4790 0.225311
#3 0.500 TRUE 5511 99.8940 100.1789 230.504 232.971 107.3707 0.463336
#4 0.750 FALSE 2 108.5000 106.0000 220.500 18.000 63.0000 1.000000
#5 1.000 TRUE 22 98.6364 95.5455 319.195 343.117 277.5887 0.838789
# Determinant PosDefinite
#1 33573.0 TRUE
#2 30638.7 TRUE
#3 42172.2 TRUE
#4 0.0 FALSE
#5 32465.6 TRUE
#To get summary stats for the whole sample, create one large inclusive group.
dsLinks$Dummy <- 1
(dsSampleSummary <- RGroupSummary(dsLinks, oName_S1, oName_S2, rName="Dummy"))
#Should return:
# Dummy Included PairCount O1Mean O2Mean O1Variance O2Variance O1O2Covariance
#1 1 TRUE 8392 98.07162 98.56864 216.466 229.2988 90.90266
# Correlation Determinant PosDefinite
#1 0.4080195 41372.1 TRUE
###
### ReadCsvNlsy79
###
## Not run:
filePathGen2 <- "~/Nlsy/Datasets/gen2-birth.csv"
ds <- ReadCsvNlsy79Gen2(filePath=filePathGen2)
## End(Not run)
``` |

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