TEDS Data Dictionary

The samples

Before the start of the TEDS26 study, "inactive" families who had never returned data were removed from the TEDS sample, which now includes 13,945 families (see 1st Contact study page). The TEDS26 study included twins from the entire TEDS sample except for the following: (a) families and individuals withdrawn from TEDS; (b) individuals who were uncontactable because of address problems and the lack of viable email addresses. "Medical exclusions", as defined for previous TEDS studies, were generally included in initial invitations but not in reminders. In families where one twin had withdrawn, or where only one twin was contactable, the contactable twin was invited to take part. Exceptions were made in only a few special cases, where for example one twin had died (and was therefore withdrawn) when it was felt inappropriate to contact the other twin.

The two twins in each family were contacted independently, even if living at the same address, with email messages and/or postal invitations addressed separately to each twin.

In TEDS26, 20962 twins were invited to take part, from a total of 10634 different TEDS families. Hence, of the 13945 families in the TEDS sample, around 3311 families were not contacted. Of these, roughly 1700 families had withdrawn; roughly 1600 were uncontactable; and around 10 were excluded because of other special family circumstances.

The TEDS26 sample included roughly 300 families in which only one twin was contacted. These families included around 80 in which one of the twins had withdrawn, and around 20 where one twin was excluded for special family circumstances; however the majority were cases where one twin was not contactable, because of address problems and absence of email addresses.

When TEDS26 data were collected, twin ages ranged from roughly 25 to 28 years.

In CATSLife, which started immediately after TEDS26 data collection had ended, all twins were invited to take part by email only. The CATSLife twin sample was based on the TEDS26 sample minus further exclusions: it excluded twins who could not be contacted by email and it excluded twins who had withdrawn or opted out during TEDS26. 14960 twins were invited to take part in CATSLife, from a total of 8164 different families. Hence, compared with the 10634 families included in TEDS26, roughly 2500 further families were not contacted. Of these, approximately 2350 twin pairs were uncontactable by email, 50 twin pairs had withdrawn from TEDS since the start of TEDS26, and 100 had opted out of TEDS26.

The CATSLife sample included roughly 1400 families in which only one twin was contacted. In addition to those mentioned above for TEDS26, nearly all of these were families in which only one of the two twins was contactable by email.

When CATSLife data were collected, twin ages ranged from roughly 26 to 29 years.

The data returns for the 26 Year studies are summarised in a separate page. There are further pages comparing samples and returns across different TEDS studies.

TEDS26 preparation and timing

Preparations for TEDS26 started in January 2021. The questionnaire (MHQ) was modelled on the questionnaire used by the GLAD study, which had been implemented on line using Qualtrics, a commercial web service used for questionnaire design. The TEDS version was also delivered via Qualtrics, hence large parts of the questionnaire could be copied from the GLAD version. After discussion among the TEDS team and collaborators, additional measures were included and some existing measures were adapted to the needs of the TEDS sample. Other adaptations were made, including a new consent form, information sheet, and an authentication process. See the annotated online questionnaire (pdf).

The focus of the questionnaire was on mental health. The measures had nearly all been used before, either in GLAD or in earlier TEDS studies, and no formal piloting of the measures was needed. However, several small-scale pilots were carried out in order to evaluate various aspects of the questionnaire including its length (these pilots are not fully documented but are mentioned on the pilot studies page).

The TEDS26 measures are described in the measures page. Additional documents desribed the measures in detail (pdf) and overlaps of the measures with other studies (pdf).

Twins were invited to take part as soon as possible after the design and testing of the online questionnaire. The first twin invitations were sent in July 2021.

Once initial invitations had been sent, a paper version of the questionnaire (pdf) was created, with the same content as the online version. Note that this includes the consent form and contact details, on the first few pages. The paper version was offered to twins, in invitations and reminders, as an alternative to the online version. Very few twins requested the paper version; however, it was subsequently sent by way of a postal reminder to targeted groups of twins.

Each individual twin was allocated a unique login code (username), for use in the online version. The online version incorporated authentication such that it could only be accessed with a valid login code, and each login code could only be used once. After logging in, a twin was first presented with a consent form accompanied by the study information sheet; the twin could not proceed to the rest of the questionnaire without first giving full consent. The design allowed each twin to complete only part of the questionnaire, after which they could log in again at a later date to continue or finish the questionnaire.

As a precaution against unexpected problems, email invitations were initially sent to just 1000 twin pairs. After evaluation of initial results, which were successful, the remaining email invitations were then sent in larger batches of thousands of twins. Twins who could not be contacted by email were then sent postal invitation letters, again asking twins to use the online questionnaire and providing them with login details.

TEDS26 data collection details

At the start of the TEDS26 study, TEDS had records of email addresses for just over 14800 twins (roughly 71% of the total). These individuals were all sent email invitations. The remainder were sent postal invitations.

In the initial twin email invitation (pdf), each twin was given their login details and a link for the web questionnaire. The initial twin (pdf) postal invitation included just a simple letter. No information sheet was included in either invitation; instead, twins were directed to read the information sheet (pdf) provided on the web site (linked both from the login page and from the consent page). At this stage, no paper booklets were sent, nor a paper consent form because twins were being asked for on line consent.

Those twins initially invited by email were subsequently invited also by post, in case the email invitation had not arrived. This second invitation was posted after twins had been sent initial email and text message reminders.

Over the entire data collection period, twins who had not yet responded were sent up to 7 email reminders, 3 text message reminders, and 1 postal reminder. The numbers of reminders sent to each individual twin depended on the availability of contact details (especially email addresses and mobile phone numbers) and on whether or not they have already responded before each reminder was sent. Many reminders included details of any forthcoming prize draw (see rewards below).

Smaller numbers of targeted twins were contacted by telephone. Target groups included twins who had been active in previous TEDS studies, particularly those whose cotwins had already completed TEDS26; and those who had started TEDS26 but not finished, especially those who had got more than half way through. The main target was to increase the number of twin pairs with data.

At later stages of the study, targeted groups of twins were also sent copies of the paper questionnaire (pdf) by post. The target groups were similar to those selected for telephoning. The paper booklet, when sent, was accompanied by an invitation letter and a paper copy of the information sheet (pdfs).

As another late-stage reminder, emails were also sent to all contactable twins and their parents, asking them to encourage all family members to take part but without disclosing whether any specific twin had already done so.

TEDS26 consent and contact details

By the time of the TEDS26 study, all twins had reached the age of at least 25 years and were adults. Twins were therefore asked individually to give consent. Parents were not involved in the data collection.

The Qualtrics questionnaire had a built-in electronic consent form, followed by requests to update contact details:

• After logging in, and before starting the questionnaire measures, each participant was required to complete a consent form.
• Linked to the consent form was a copy of the information sheet describing the study.
• In order to consent, the participant was required to tick boxes to say that they had read the information sheet and agreed to their data being used in the ways described, then to click on a button to confirm.
• After consent, each participant was asked to provide their email address.
• Each participant was then asked for an optional mobile phone number.
• Each participant was then presented with the address currently held in the TEDS admin records, and was asked whether it was correct.
• If the answer was no, the participant was asked to record their correct address.
• Each twin was then asked whether the address given was also that of their parent(s), so that TEDS could keep track of which twins were still living with parents.

The paper booklet included, in its initial pages, paper versions of the consent and contact details forms, and these were checked by TEDS admin staff on return of completed booklets.

Whichever version was used, the contact details were extracted and used to update the TEDS admin database for future contacts with each participant.

Another early section of the questionnaire asked for information about the twins' children or pregnancies. This information was gathered for the CoTEDS (Children of TEDS) study. Details were extracted from the questionnaires and passed to the CoTEDS team, who subsequently contacted families for consent to join the CoTEDS study and entered relevant details in the TEDS admin database.

The wording of the consent form, contact details questions, and CoTEDS questions, may be seen within the paper questionnaire and the online questionnaire (pdfs).

TEDS26 twin rewards

In TEDS26, each participating twin was offered a £10 electronic Flexecode voucher on completion of the questionnaire. However, as in previous studies, twins were asked whether they wanted to decline some or all of this reward, and were given three options: taking the £10 reward, taking only £5, or forfeiting the entire reward. We do this because many twins have previously told us they prefer that we retain their reward to benefit future research. This voucher choice was offered immediately after completion of the online questionnaire; for the paper version, the choice was offered as a question at the end of the questionnaire. Twins who failed to express a choice, but who nevertheless completed the questionnaire, were sent the £10 reward by default. The wording of the twin reward choice question may be seen on the last pages of both the paper questionnaire and the online questionnaire (links above).

Twins were also offered entries in 7 prize draws, held at intervals during the data collection period. The deadline, and the nature of the prizes, for each prize draw were stated in relevant reminders. In each prize draw, each twin was given a single entry for completion of the questionnaire before the prize draw date. Each twin who had finished was given an entry in every prize draw that followed, so twins who finished at an early date were entered in many of the prize draws.

Prizes were generally awarded in pairs. For each available prize, an eligible twin was randomly selected as the winner, and their co-twin was given the same prize if s/he had also completed the questionnaire. This mechanism was explained to twins in the hope of encouraging more twin pairs to finish the questionnaire: twins effectively had two entries in each prize draw if both twins had finished the questionnaire.

CATSLife preparation and timing

Practical preparations for CATSLife started late in 2022, with testing of the web activities. These included the Spatial Spy activity, which was a shortened and updated version of the TEDS Navigation study (part of the 18 Year study). They also included four TestMyBrain activities, designed by Many Brains and previously used with other non-TEDS study samples.

On successful conclusion of the testing with some bug corrections, preparations were made to start CATSLife data collection as soon as TEDS26 data collection had ended. Twins were invited in three waves, the earliest wave including twin pairs who had completed TEDS26 at least six months previously. Invitations for the first wave were sent at the end of January 2023, and invitations for the second and third waves were sent in March and April 2023 respectively. Data collection continued until the end of 2023 (see below for details).

As in TEDS26, each individual twin was allocated a unique CATSLife login code (username). The web tests could only be attempted after authentication with a valid login code, and each login code could be used only once. After logging in, a twin was first presented with a consent form accompanied by the study information sheet; the twin could not proceed to the rest of the activities without first giving full consent. The design allowed twins to pause after each test if they wished, after which they could log in again at a later date to continue or finish the tests.

CATSLife data collection details

The CATSLife twin web activities were presented as a single battery of tests to the twins, but technically they were implemented on two servers. The login, consent, Spatial Spy activity and feedback questions were implemented by web design and hosting company called Quodit, run by former TEDS researcher Nic Shakeshaft, and previously used for the TEDS g-game and covid studies (see 21 Year study). After initial consent, twins were automatically redirected from the Quodit server to the TestMyBrain server for a short battery of four tests, before being redirected back to the Quodit server for the Spatial Spy activity.

The Spatial Spy activity was a shortened and adapted version of the TEDS 18 Year Navigation study, designed by TEDS researchers. This typically took between 10 and 15 minutes to complete. For details of the activity, see the Spatial Spy page.

The TestMyBrain activities were designed by Many Brains and had previously been used in study samples other than TEDS. For details of the activities, see the TestMyBrain page. There were four short tests, which could all typically be completed within 15 minutes. Hence, the entire TEDS CATSLife battery could be completed within roughly 30 minutes.

Twins were invited to take part by email. The first wave of invitations included twin pairs who had completed TEDS26 at least six months previously, and these were sent in late January 2023. The second and third waves of invitations included twins who had completed TEDS26 more recently, as well as twins who had not taken part in TEDS26, and these invitations were sent during March and April 2023.

In the invitation email, each twin was sent their unique login code and a link (on the Quodit server) for logging in and starting the activities. After logging in, every twin was required to complete the consent form (pdf) before being able to continue to the test activities. The consent page had a link to the information sheet (pdf), which twins were asked to read before giving their consent. Amongst other things, the information sheet explained that the tests were implemented on the Quodit and Many Brains servers, with redirection between the two, and with appropriate data protection measures in place.

During the course of data collection, twins who had not responded to the initial invitation were sent up to 4 email reminders and 2 text message reminders. Most reminders included notifications of forthcoming prize draws (see below).

The Spatial Spy activity was designed to be used on a laptop or desktop computer, with a reasonably large screen, and not on a mobile phone or tablet. This was largely because the activities required the use of a pointer device (mouse or trackpad), not a touch screen. It was also because the written instructions on screen were not designed to adjust for small screens, so they would be very difficult to read on a mobile phone screen. Therefore, twins were given prompts and reminders to use a laptop/desktop not a mobile phone for this activity: these were included in the invitation and information sheet, and appeared several times on screen before the start of Spatial Spy.

After the Spatial Spy and TestMyBrain tests, the CATSLife web battery ended with a small number of feedback questions (pdf). These included two quality control questions, asking whether twins had had any distractions from the tests, as well as the voucher reward choice question.

CATSLife twin rewards

In CATSLife, each participating twin was offered a £10 electronic Flexecode voucher on completion of the questionnaire. However, twins were asked to consider whether to decline this reward, and were asked to choose between two options: either to take the £10 reward, or to forfeit it. This choice was offered immediately after completion of the online questionnaire (see feedback questions) (pdf).

Twins were also offered entries in two prize draws, held at intervals during the data collection period. The deadline, and the nature of the prizes, for each prize draw were stated in relevant reminders. In each prize draw, each twin was given a single entry for completion of the tests. Each twin who had finished was given an entry in every prize draw that followed, so twins who finished at an early date were entered in all of the prize draws.

As in TEDS26, prizes were generally awarded in pairs. For each available prize, an eligible twin was randomly selected as the winner, and their co-twin was given the same prize if s/he had also completed the activities. This mechanism was explained to twins in the hope of encouraging more twin pairs to finish the battery: twins effectively had two entries in each prize draw if both twins had finished.

Data entry

General data entry issues (for all TEDS studies) are described in a separate page.

Twins who participated online effectively entered their data themselves. In TEDS26, twin responses were submitted from their devices to a database running on the Qualtrics server. From the server, TEDS admin staff were able to download files containing all data recorded in the questionnaire. Similarly, in CATSLife, twin responses were submitted to database on the Quodit and Many Brains servers, and were subsequently downloaded by TEDS staff. Further details are given in the 26 Year data files page.

In TEDS26, the raw data files downloaded from the server were also the source of important admin data. As described above, each TEDS26 participant was asked for email, phone and address details; twins were asked for their reward preferences; and participants were asked for details of their children (or pregnancy) for the CoTEDS study. All these details, where given, were used to update the TEDS admin database, generally by a process of copying and pasting but with manual input for the purpose of data cleaning. For example, new contact details were compared carefully with existing details, and obvious typos and formatting anomalies were corrected.

TEDS26 paper questionnaires were returned by post to the TEDS office. Data entry was then carried out by TEDS admin staff by manually keying responses from the paper questionnaire into the Qualtrics system, using the given twin's login. Hence, the data file downloaded from Qualtrics ultimately included all twin data, whether returned online or by post. This then significantly simplified the process of dataset construction.

In conclusion, the raw data from the 26 Year study (both TEDS26 and CATSLife) have been stored in files downloaded from web servers. After data collection, all data have been subjected to data cleaning, both at the stage of data entry (for paper booklets) and at the stage of dataset construction. For a discussion of general data cleaning issues in the TEDS data, see the data cleaning page.