TEDS Data Dictionary

10 Year Study

Contents of this page:


The 10 Year study data were collected in the following ways:

  • Twin web tests.
    Cognitive and other tests completed by twins over the Internet.
  • Parent web questionnaire.
    A very short questionnaire about the parents themselves, completed over the Internet.
  • Teacher questionnaires.
    Teacher-reported data relating to the twins, collected on paper.

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

The 10 Year data were collected between 2003 and 2005 from TEDS families with twins born between January 1994 and August 1995. Data collection was timed to coincide with the school year in which the twins reached their 10th birthdays.

The sample

The sample for the 10 Year Study was restricted to just two cohorts:

  • Cohort 1: twins born between January and August 1994 (data collected 2003/04)
  • Cohort 2: twins born between September 1994 and August 1995 (data collected 2004/05)

Hence, the latter part of the 1995 cohort, and the whole of the 1996 cohort, were omitted from this study.

The cohort 1 study sample was restricted to families that had participated in the 9 Year study. Families were included if they had returned initial consent at age 9 (regardless of whether they subsequently returned booklets). Therefore, as in the 9 Year study in cohort 1, the following families were excluded from the 10 Year study: (a) those that had withdrawn from TEDS; (b) those with address problems, who could not be traced; (c) families in which either twin had a severe medical condition; (d) families with overseas addresses. Additionally, families were excluded from the 10 Year study in cohort 1 if they had failed to return consent in the 9 Year study.

The cohort 2 study sample was broadened to include all families except for the following: (a) those that had withdrawn from TEDS; (b) "inactive" families, who had not returned data in any previous studies; (c) families with address and phone problems, who could not be contacted. The cohort 2 sample was therefore much more inclusive than the cohort 1 sample.

Initial contact (by consent form, login pack, or telephone call) was made with 5944 of the 9411 families from the original TEDS sample from ONS, in cohorts 1 and 2. Hence there were nearly 3500 families that were not contacted. Of these, roughly 950 had withdrawn; roughly 900 were inactive (no previous data returned); roughly 650 were address and/or phone problems that could not be contacted; around 100 were excluded on medical grounds; around 50 were excluded because they lived overseas; and the remainder (around 850) had not participated in the 9 Year study (they had either not been invited, or they failed to return consent).

The data returns for the 10 Year study are summarised in a separate page. There are further pages comparing samples and returns for different TEDS studies.

Data collection

Data collection periods were linked to the school year (September to August) in which twins reached the age of 10 years. The reason for this was to ensure that all twins were in the same school year when the teacher data were collected. Hence, families were divided into school cohorts according to when their twins were born (as described above). This simplified administration of the study, because all families in a cohort could be contacted at once. Twin ages varied from roughly nine and a half to ten and a half years, at the time when the data were collected.

For families not known to have address problems, initial contact was made by sending them an information pack together with a consent form (pdf); the latter was printed on a postage-paid postcard. In the consent form, parents were asked to consent to (or opt out of) the web study; and they were also asked for consent to contact the twins' teachers (they were also asked to provide teacher/school contact details). Up to two written reminders were sent to families that did not return the consent forms promptly.

Every family that had not explicitly opted out of the study was later sent a login pack. This pack contained the family's login details (username and password) for the web activities, and a guidance sheet (pdf). The latter contained basic instructions for accessing the web tests.

All families that had been sent a login pack, plus families with address problems that had not been contacted by mail, were subsequently contacted by telephone. This was done by "web callers", staff employed by TEDS to contact the families involved in the web study, in order to encourage them to complete the web activities and to help them with problems. Full details of the web tests, including a description of the role of the web callers, are on a separate page.

On completion of the web tests, each twin was rewarded with vouchers (to the value of £5 for each twin). A further £5 voucher was included for the parents, as a way of covering their internet connection costs.

The progress of each family in their web activities was recorded on the web server. For administrative purposes (for example, in order to allocate families to web callers, and in order to organize mailings of vouchers), information had to be transferred from the web server to the TEDS administrative database. This was done by means of a "family status file", which was produced automatically every night by a program running on the web server. The analysis file was a plain text file (in csv format), with a row of data for every family. The information recorded for each family included fields to show whether each twin had started or finished each of the web tests, together with dates, times, and other information.

The teacher study included all families that had given consent and provided contact details for the twins' teachers and schools. Families may have done this in writing via the consent form, or verbally via the web callers. Teacher questionnaires (pdf) were sent directly to teachers, and were not seen by the families themselves. Up to three written reminders were sent to teachers that had not returned their questionnaires promptly. A telephone reminder was also used for teachers in some prioritized cases.

The measures used in the web activities and teacher questionnaires are described in detail on another page.

Data entry

General data entry issues (for all studies) are described in a separate page. In the 10 Year study, data from the web activities were effectively entered by the parents and twins themselves. As they answered items on their computers, their responses were recorded on the TEDS web server.

The web server was programmed to produce, when required, "analysis files" containing the web test data. There was a specific analysis file for each web activity. Each analysis file is a plain text file, with comma-delimited variables, containing one row of data for each twin who completed the test. The analysis files were copied from the web server when they were needed for construction of the dataset. The data files are described in detail in another page.

The teacher questionnaires were entered by means of optical scanning. The layout of the questionnaires had been designed with this in mind. The scanning was handled externally by Group Sigma, a commercial company. The questionnaires were returned by mail from teachers to the TEDS office. They were then delivered to Group Sigma in batches for scanning. After scanning each batch of booklets, Group Sigma returned the data in plain text files (the data files are described in detail in another page).

The annotated version of the teacher questionnaire (pdf) shows, in green, the scan positions used for each field in the Group Sigma raw data files. It also shows, in blue, the field names and value codes that have been used in the cleaned raw data.

The files of raw scanned data, as returned by Group Sigma, have been retained for reference. After data cleaning, the teacher data were aggregated and stored in a single Access database file. This Access database is now treated as the master copy or source of all 10 Year teacher data to be used in analysis. Note however that the raw web data (in analysis files) is stored separately, partly because of the large size of these files. All the raw data files are described in full in 10 Year raw data files.