TEDS Data Dictionary

2 Year Study

Contents of this page:

Introduction

The 2 Year study data were collected by means of booklets:

  • Parent booklets.
    Parent-reported data, relating mainly to the family (but with some twin-specific items).
  • Twin booklets.
    Parent-reported data specific to each twin, including various language and behaviour measures. Included the "Parca" parent-administered cognitive tests.

The measures used in the booklets are described in full in a separate page.

The 2 Year data were collected between 1996 and 1997 from TEDS families with twins born between 1994 and 1995. Data collection was timed to coincide as closely as possible with the twins' 2nd birthdays.

The sample

The 2 Year sample only included families of twins born in 1994 and 1995 (not 1996).

The 2 Year booklets were sent to all families in these cohorts, except for around 700 families that had withdrawn or were known to be address problems. As a general rule, the 2 Year booklets were sent regardless of whether or not families had returned the 1st Contact booklets.

The data returns for the 2 Year study are summarised in a separate page. This page also describes how some entered data appears to have been lost for this study.

There are further pages comparing samples and returns for different TEDS studies.

Data collection

Each family in the sample was sent three booklets: a parent booklet plus two copies of the child booklet (pdfs). The parent booklet included a consent form on the first page. The measures used in the booklets are described in detail on another page. The measures were entirely parent-reported, although the child booklet included cognitive tests that were administered by the parents on the children.

The booklets were designed to be completed when the twins were precisely 2 years old; they were therefore sent to families at or just before the twins' 2nd birthdays. This involved regular mailings of booklets (generally once per month) during 1996 and 1997.

Regular reminders were sent to families who did not return the booklets promptly. Up to 8 reminders were sent, over a period up to 11 months after the original booklets were sent to each family.

Data entry

General data entry issues are described in another page. For the 2 Year study, in the 1994 cohort, data from the booklets were entered by TEDS staff into a Microsoft Access database. In the 1995 cohort, data entry was handled externally by NOP Numbers, a commercial company; it is not clear what type of software system they used for data entry, but the entered data were returned in Excel spreadsheets.

Data entry staff, both in TEDS and at NOP, carried out basic coding of the raw data by converting tick boxes to numeric code values - see 2 Year item coding for the parent and child booklets (pdfs). The Drawing task items in the child booklet were scored by TEDS staff before the booklets were sent to NOP. There is no surviving manual of coding instructions for data entry staff, other than paper versions of the pdf documents linked above.

The inside front cover of the 2 Year parent booklet asked for contact details of a relative or friend of the family; and the first page of the booklet is a consent form, asking for family name and address details. Page 1 also asked for new sibling details. The verbatim text data from these sections were transferred into the TEDS admin system at the time of data collection, but have not been retained within the raw data files.

The few other text fields, within the body of the booklets were not and are not present in the raw data.

The original raw data files were cleaned and aggregated together, and stored in a single Access database file (see 2 Year raw data files for further details). This latter Access database is now the master copy of all 2 Year raw data for construction of the dataset. The ways in which the raw data have been cleaned is described in another page.