The 1st Contact study was (in all but a few cases) the first point of contact between TEDS and the 16810 families in the ONS sample. As explained above, the 1st Contact study started and continued while families were being recruited by ONS.
The 16810 families in the ONS sample (with a few exceptions, see below) were invited to take part in the 1st Contact study; hence the study included all families in the TEDS sample, with twin births between January 1994 and December 1996. This initial 1st Contact data collection took place between 1995 and 1998. Data collection was not precisely timed to coincide with a particular twin age, but most twins were aged between 1 and 2 years when the booklets were returned, with a median age of around 1.6 years. Since 1998 there have been several further attempts to collect the data from families that did not respond in the initial phase.
The data for this study was collected in a single booklet (pdf), to be completed by the parent or guardian of the twins. The booklet included a consent form on the first page. The booklet was sent along with a covering letter and an information leaflet (pdfs). The pack was addressed to the contact parent identified by ONS, but it was not necessary for the same parent to complete the booklet.
Regular reminders were sent to families who did not return the booklet promptly. Up to 6 reminders were sent, over a period up to 11 months after the original booklet was sent to each family.
TEDS sent the 1st Contact booklet to all except roughly 500 of the 16810 families in the ONS sample. The 500 or so exceptions can be explained in various ways. In some cases, the postcards returned to ONS contained ambiguous responses, or were spoiled in some way. When TEDS contacted these families for clarification, before sending the 1st Contact booklet, a few of them changed their minds and withdrew from TEDS. Other families returned their postcards late, and were sent the 2 Year booklets before the 1st Contact booklet (because the twins had reached their second birthdays); some of these families withdrew from TEDS, or became address problems, before the 1st Contact booklet could be sent. In all, around 450 families withdrew from TEDS, and around 50 became address problems, before the 1st Contact booklet could be sent.
Because of the essential nature of the TEDS 1st Contact data, there have been several further attempts to collect the data from families who did not return it when first asked (especially if they returned valuable data in a later study). In the "You and Your Family" study, carried out in 2000 and 2001, a shortened form (pdf) of the 1st Contact booklet was mailed to families that had returned data at ages 2, 3 or 4, but had not returned the original 1st Contact booklet (it was renamed to "You and Your Family" because it was no longer the first contact with the family). Between 2004 and 2006, telephone interviews were used to gather the data, using the same shortened form of the booklet; especially from families that had returned data at age 7 or later. In 2013, another attempt was made to collect 1st contact data (by post and by telephone), using an even shorter version of the booklet; targeted families were those that had participated at 12, 14 or 16.
General data entry issues are described in another page. Initially (for the 1994 cohort and some of the 1995 cohort), 1st Contact booklets were entered in-house by TEDS staff. This data entry was done using Microsoft Access databases, which were specifically designed for this purpose. Later in the study, data entry was handled externally by a commercial company called NOP Numbers. They used their own data-entry software system, and returned the data to TEDS in Excel spreadsheet files. These 1st Contact data files are described in another page.
In all booklets, the "job title" responses for the parents were numerically coded using SOC and social class coding before data entry. This was done by TEDS staff, even for the later booklets that were sent to NOP Numbers for data entry.
The coding for the remainder of the 1st Contact booklet comprised the conversion of tick-box responses to numerical codes. This coding was done by the data-entry staff themselves, both in TEDS and at NOP. To assist with this coding, a document of coding instructions (pdf) was provided. A coding manual (pdf) was also provided (this refers specifically to table names NUMERIC1 and NUMERIC2 in the early Access database).
Entry of verbatim text data was not consistent between cohorts and between all parts of the booklet. Initially, while data entry was being handled in TEDS, verbatim text was not entered. Instead, presence of a text response was denoted using the coded value "1" in the electronic data. In the later stages, while data entry was being handled at NOP, many (but not all) verbatim text responses were in fact entered. These were entered after TEDS researchers and collaborators had expressed interest in particular text item responses. A full list of verbatim text items, and the extent to which they were entered, is provided in another page.
There is also an annotated version of the 1st Contact booklet, showing the coding of the raw data (pdf) for all except the text items referred to above.
The raw data from all the families has been aggregated and stored in a single Microsoft Access database file, and data cleaning has been carried out on the data stored here. This Access database is now treated as the master copy or source of all 1st Contact data to be used in analysis. The original raw data files, and the Access database, are described in full in the data files page.
Data from the later data collections (2004 to 2006, 2013) have been directly entered into this same Access database. The database incorporates forms and programs that enforce various data rules, to ensure that only clean data can be entered.