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 3 years old; they were therefore sent to families at or just before the twins' 3rd birthdays. This involved regular mailings of booklets (generally once per month) during 1997 and 1998.
Regular reminders were sent to families who did not return the booklets promptly. Up to 5 reminders were sent, over a period up to 11 months after the original booklets were sent to each family.
General data entry issues are described in another page. In the 3 Year study, nearly all data entry was handled externally by NOP Numbers, a commercial company. A few late booklet returns, and incomplete sets of family booklets, were entered in-house by TEDS staff. The raw data have been saved in pre-formatted Excel workbooks containing multiple worksheets. It is not clear whether the data were entered directly into Excel at NOP Numbers, or whether the data were exported into Excel after data entry into some other software system.
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 3 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, and the coding rules for these items are fully described in 3 Year Drawing coding (pdf).
The inside front cover of the 3 Year parent booklet asks 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. The verbatim text data from these two pages was entered and does exist in the raw electronic data. However, this does not form part of the dataset, and was only entered so it could be used for administrative purposes. At the time of the 3 Year study, these data were used to update the TEDS admin database.
In the main body of the parent booklet, and in the child booklet, there are just a few items where a free text response is invited. However, the verbatim text from these items was not entered, so does not exist in the electronic data.
The original raw data, as entered and before cleaning, still exist in Excel files. These data have been copied, cleaned and aggregated together, and stored in a single Access database file (see 3 Year raw data files for further details). This latter Access database is now treated as the master copy or source of all 3 Year data to be used in analysis. The ways in which the raw data have been cleaned is described in another page.