TEDS Data Dictionary

1st Contact Study

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The 1st Contact study was, in nearly all cases, the first occasion on which TEDS families were contacted directly by TEDS, and the first occasion on which they were asked to provide data. To a large extent, the sample of families that returned the 1st Contact data defined the TEDS sample for subsequent studies.

Before the 1st Contact study could take place, families had to be recruited into the TEDS sample. The recruitment process, involving ONS, is described in more detail below. Recruitment and the 1st Contact study were taking place in parallel over a period of roughly three years, from 1995 to 1998; in most cases, a family would be sent the 1st Contact booklet soon after having been recruited into TEDS, typically when twins were around a year and a half old.

The 1st Contact study data were collected by means of a single parent booklet. The booklet contains both family-specific and twin-specific items. The measures used in the booklet are described in full in a separate page.

Recruiting the TEDS sample

Coinciding with the start of the TEDS study, the OPCS (Office of Population, Censuses and Surveys), soon renamed to the ONS (Office for National Statistics), set up a national register of twins, triplets and other multiple births, called the National Twins Plus Register.

Once TEDS had obtained funding from the MRC (Medical Research Council), ONS agreed to ask families of twins to give consent for joining TEDS at the same time as asking them for consent for joining Twins Plus. ONS agreed to do this for all recorded and traceable live twin births in England and Wales between January 1994 and December 1996. Hence the initial contact with families, by ONS, was to invite each family to take part in either or both of TEDS and the Twins Plus Register.

ONS sent each family a pack including the following materials:

The reply card had two tick boxes in which parents could express an interest in the Twins Plus Register and in TEDS respectively; it also had a space in which parents could record address changes. The cards were returned to ONS, not to TEDS.

For those families who ticked the box expressing an interest in TEDS, ONS would record the essential details to be passed on to TEDS: the forename, surname and address of the parent would had been contacted (who would become the "contact parent" in TEDS); the names, birth order and dates of birth of the two twins; and an ID assigned by ONS to the family. Periodically during the recruitment process, ONS would compile these details of newly recruited families into a spreadsheet list. The list would then be saved (usually as a delimited text file) onto a floppy disk, which was then posted to the TEDS office accompanied by a letter. The surviving files sent in this way, and scanned copies of the letters, have now been archived in TEDS.

On receipt of these files, the details of the parents and twins were added to the TEDS admin database. In the TEDS database, each family was assigned a unique ID number (the FamilyID, with 4 or 5 digits) and each twin was additionally assigned a unique ID number (the TwinID, with 7 or 8 digits comprising the FamilyID followed by a 3 further digits). The original ONS family IDs (containing both letters and numbers) were not used further in TEDS except in the event of correspondence with ONS, for example to exchange details of address changes.

Hence, over the course of recruitment and correspondence with ONS, the original TEDS sample of 16,810 families was collected and added to the TEDS admin database. This is sometimes referred to in TEDS as the "ONS sample". These were the 16810 families that formed the sample for the 1st Contact study.

Data collection

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.

There are further pages describing the 1st Contact data returns, and comparisons of samples and returns for different TEDS studies.

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.

Data entry

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.