The Sample:
580 twin families were initially recruited as subjects for one of
two studies of infant twins, the Twin Infant Project, or the MacArthur
Longitudinal Twin Study (MALTS). Twins were born between Aug. 9th, 1984,
and Dec. 12, 1990 in the state of Colorado.
Twins were preferentially selected for high birthweight (greater than
1750 grams) and overall good health at the time of initial testing. Of
these 580, 483 twin families are considered the foundation sample for the
Longitudinal Twin Studies (the other 98 were either pilot families, or
Twin Infant Project families). For more information about sample recruitment
and history,
click
here. The formation of the LTS sample is described formally by
Rhea et al. (2006) in Twin Research and Human Genetics, Volume 9,
pages 941-949.
To obtain the file containing basic demographic data for the sample of
483 foundation LTS families,
click here.
The ID System:
The LTS twins have a five-digit twin identification number. The first
three digits are the family number, which ranges between 013 and 813 for twins
tested during childhood. The fourth digit is either a 1 or a 2, to
indicate whether the twin has been treated as the first or second twin for
identification purposes. This number is
NOT necessarily a reflection
of birth order, since some attempt was made to randomize the numbering of
the twins. The fifth digit is the sex of the twins, either a 0 for
female twins, or 1 for male twins. Because only same-sex twins were recruited
for the LTS sample, both twins in the twin pair should have the same sex
code. Putting the pieces together, the Twinid 09811 refers to the first
twin in family 098, who is male.
Please note: Family and Twinid
are treated as alphanumeric variables to preserve the leading 0s. Their
numerical equivalents are Nfam and NID.
Zygosity Determination:
Each time the twin pair was tested, the similarity of the twins was evaluated
using a ten-item assessment completed by each rater who saw the twins.
This form is similar to that developed by Nichols
& Bilbro (1966). When pairs had been rated at least four times,
zygosity was assigned if 85% or more of raters were in agreement. Subsequently,
nearly 400 of the longitudinally-followed twin pairs have had their zygosity
confirmed using a panel of 9 or more highly polymorphic Simple Tandem Repeat
markers. This file contains zygosity linked to individual IDs for both LTS & CTS (community twins).
Individual Twin Zygosity
SPSS Export File
Parent Testing:
Participating parents were given an IQ test, a specific cognitive
abilities battery, and a personality, health, and demographics
battery during the course of TIP/LTS. LTS parents participating
in TIP were given the IQ test and the specific cognitive abilities
battery during the first year of the twins' lives. LTS parents
recruited subsequent to TIP were primarily given an IQ test and
cognitive battery at twin age 7 years. The personality, health,
and demographics battery for the parents was collected as a
questionnaire around the time of the twins' 2nd birthday.
Twin Testing:
Approximately 15% of the twins were initially tested using the Colorado
Adoption Project protocol at ages 1, 2, and 3. SPSS Export files of their
data can be downloaded by clicking on the following links:
The remaining twins were initially tested using the MacArthur Longitudinal
Twin Study protocols at 14 months, 20 months, 24 months, and 3 years of
age. For a detailed description of the procedures used at each age
point click on the links below.
Accessing the data:
14 Month, 20 Month, 24 Month, 36 Month(3 Year), 5 Year, and 7 Year data:
MALTS twin data for home and lab procedures are combined into an
age-specific SPSS Export file with controlled access. The data can be
combined across waves/ages by merging on twinid (a five-character
alphanumeric variable). Each year's data has a unique prefix, e.g.,
V1 for 14 Month, Y3 for 36 Month.
Year 4 (48 Month) data:
At age 4, all the twins were tested using the Colorado Adoption Project
protocol. An SPSS Export file of the total twin data set for year 4
can be downloaded by clicking on the link below:
Years 7-15 data:
For years 7, 9, 10, 11, 12, 13, 14, & 15, all LTS twins were tested using protocols similar to those used for the Colorado Adoption Project. SPSS Export files can be downloaded by clicking on the
appropriate link below:
Year 16 data:
At age 16, all twins were tested using the Colorado Adoption Project
protocol. Year 16 represents the lead-up year to CADD and Executive
Function testing (typically age 17), and the
conclusion of the normative yearly testing protocols.
An SPSS Export file of the total twin data set for year 16
can be downloaded by clicking on the link below:
Using the data:
All LTS collaborators have a responsibility to use the LTS data responsibly,
including restricting access to these files to those colleagues who have
requested and received permission to work with the data.
Click here to obtain information about how to
request permission to work with the LTS data set.
Analytic Methods:
Sample programs are available for both simple data management tasks,
such as combining data across ages or splitting the individual twin
level file into a paired file, and for doing twin analyses.
Click here to obtain information about how
to obtain sample programs for working with the LTS data set.
