TEDS Data Dictionary

2 Year Study

Contents of this page:


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The 2 Year booklets were sent to all families in these cohorts, except for around 700 families that had withdrawn or were known to be address problems.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 7 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 raw data 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.

Entry of verbatim text data (from the parent booklet) differed between the two cohorts. In the 1994 cohort, all verbatim text data was entered and recorded in the Access database. However in the 1995 cohort, the only verbatim text items entered (in Excel) were the family contact details (from the consent form), the twin names (raw items AN28 and AN29), and contact details for a relative or friend (from the final page of the booklet). In both cohorts, a coded numeric item was entered for each text item in the parent booklet, with value 1 if a text response had been made by the parent, or value -77 if not. These coded items are shown in the parent booklet raw item coding (pdf).

The original raw data, as entered and before cleaning, still exist in Access and Excel files. These data have been 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 treated as the master copy or source of all 2 Year data to be used in analysis. The ways in which the raw data have been cleaned is described in another page.