TEDS Data Dictionary

Description of Test

This test is designed to measure the speed of twins' reactions to stimuli presented on screen. In each item of this test, an image showing a number (from 1 to 4) is presented on screen. Twins respond by pressing the corresponding number key (1, 2, 3 or 4) at the top of the keyboard. As this is a measure of reaction time, twins are encouraged to react by pressing the appropriate key as quickly as they can after the number appears on screen.

To prevent twins from anticipating when the number image will appear, the screen remains blank for a short, apparently random time interval first. This time interval may be 1, 2 or 3 seconds for different items. The time interval is not in fact random but is predetermined so that every twin receives the same stimulous for each item. The time intervals are tabulated in the table of items below.

Each number image remains on screen for 8 seconds. If a twin takes longer than 8 seconds to respond, then the item is timed out. When this happens, the item is forfeited with zero score and the test proceeds directly to the next item.

The twins are asked to attempt 6 practice items before they proceed to the main test, with feedback to tell them whether they gave correct responses (no feedback is given in the main test). Twins may repeat the practice items before they start the main test if they wish.

The main test consists of 40 items. Items are presented in item number order, from 1 to 40, without any branching or discontinue rules. The test is very short, so there is no "come back later" option once the test has been started.

Because of the way the items are presented, under strict timed conditions, the test runs entirely in the twin's web browser and data are only sent back to the server once the test is finished. As a result, if the test is interrupted in any way once it has started then the test ends without any data being recorded, and the test cannot be resumed or re-started. The test is then labelled as "abandoned", and no data are recorded. The twin then resumes the web battery at the next activity. Any of the following may cause the test to be abandoned, once started: twin's computer crashes; server software crashes; loss of internet connection; browser closed during test; twin clicks browser's Back or Refresh buttons.

After timing out on an item in this test, the next item automatically appears on screen. If a twin fails to make any response, then it is possible for a whole series of items to time out in sequence, so "serial timeouts" may occur in this test. Such cases are excluded from the data if the number of timeouts is judged to be too large.

Test Rules

• Scoring
  For each question, the correct response is given a score of 1, and an incorrect response or a timeout is given a score of 0. The practice items do not contribute to the total test score. The total test score is the sum of the item scores for items 1 to 40. The maximum total score for the test is 40.
• Responses
  Only the keys 1, 2, 3 and 4 at the top of the keyboard will register any response. In the raw data, responses are recorded in numeric form as 1, 2, 3 or 4, or 5 if timed out.
• Timeout rule
  A timeout of 8 seconds applies to each item. After 8 seconds with no response, the item is forfeited with zero score, and the next item appears automatically on screen.

Item Variables

The item variables relating to the Reaction Times test, as listed in the table below, were generated automatically by programs on the web server during the course of the test. Note that the dataset only includes data for completed tests. It is not possible to leave this test partly-completed. However, the test may be abandoned in which case no test data are recorded. Tests with a large number of serial timeouts are also excluded, in which case the test data have been deleted.

In most cases the values of these variables have been left unaltered, although some have been recoded during data cleaning as follows. See the web data cleaning page for further details.

• For timed out items, the item response variable is recoded from 5 to -1, and the item answer time is recoded from 8 to missing (item scores are 0)
• For items that crashed or malfunctioned in any way, the item response variable is recoded from missing to -4, and the item score is recoded from missing to 0.
• For twins identified as random responders in this test, the status flag is recoded from 2 to 4, the data flag is recoded from 1 to 0, and all item variables are recoded to missing (test data deleted)
• For tests that were abandoned or crashed, and tests where serial timeouts occurred, the test status flag is recoded from 2 to 3, the data flag is recoded from 1 to 0, and all item variables are recoded to missing (test data deleted)

The test start and end dates and times, and item answer times, have not been retained in the dataset.

Test Items

There are 40 items in the main part of the test. Each number (1, 2, 3 and 4) appears on screen in 10 of the items. The numbers are presented on screen as images, each of which is the same size and appears in the same position. The time interval prior to each number appearing on screen varies from item to item, and is 1, 2 or 3 seconds.