TEDS Data Dictionary

Description of Test

The image below is an example item from the Number Line test:

Every item is presented in the same format: a number (in this case 818) is shown the top of the screen, above a straight line representing the numbers from 0 to 1000. The twin must click on the number line, to estimate where the displayed number is positioned in the range 0 to 1000. A thin vertical red line, as shown in the image above, moves with the mouse pointer to help the twin to decide where exactly to click.

In the test introduction, the twins are asked to attempt a practice item before they proceed to the main test, with visual feedback to show them how close their response was to the correct position on the line (no feedback is given in the main test). Twins may repeat the practice item before they start the main test if they wish.

At the end of each item response, when the twin has clicked on the line, an intermediate screen appears and twins can choose either to "come back later" or to "continue" with the next item.

The main test consists of 22 items. Items are presented in item number order, from 1 to 22, without any branching or discontinue rules. There is no time limit for responding to each item, so item timeouts do not occur. The items are presented in full in the table below.

Test Rules

• Responses
  The position where a twin clicks on the number line is converted to the whole number between 0 and 1000 representing the position of the click on the line. This number is stored as the item response.
• Scoring
  For each item, the recorded 'score' is computed by subtracting the target number (as displayed on item page) from the response. Hence successful twin item estimates gain scores close to zero, and inaccurate estimates gain scores far from zero (either positive or negative).
  The total test score is mean of the absolute (positive) values of the item scores, rounded to one decimal place. Most test scores lie in the range 10 to 100.

Item Variables

The item variables relating to the Number Line 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. If a twin started the test but left it unfinished, then the data for the test were not used.

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 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.
• In rare cases when the test crashed repeatedly in a series of items, so that insufficient data were collected for a meaningful test score, 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)
• 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)

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

Test Items