Description of Test
In each item of this test, an image showing a number (from 1 to 9) and some dots is presented on screen for just 2 seconds. During that time, the twin must decide whether or not the presented number matches the number of dots; the time interval of 2 seconds is designed to give twins time only to make an estimate, not to be able to count the dots. To respond, the twin must press a keyboard key (F or J) to indicate whether they match or not. This response must be given within the 2 seconds in which the stimulous remains on screen, otherwise the item times out and the next item is presented.
The introduction to the test asks twins whether they are right- or left-handed. For right-handed twins, they are asked to press the J key for a match, and the F key for a non-match. For left-handed twins, F means match and J means non-match.
The twins are asked to attempt a minimum of 4 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 practice items before they start the main test if they wish.
The main test consists of 36 items, but only items 5 to 36 contribute to the overall score (items 1 to 4 are treated as further practice items). Items are presented in item number order, from 1 to 36, 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. The questions are presented in full in the table below.
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, and main test items 1 to 4, do not contribute to the total test score. The total test score is the sum of the item scores for items 5 to 36. The maximum total score for the test is 32. - Responses
Only the keyboard keys F and J will register any response. Responses are recorded in coded form as 1=match (J if right-handed, F if left-handed), 2=no match (F if right-handed, J if left-handed) or 3=timed out in the raw data. - Timeout rule
A timeout of 2 seconds applies to each item. After 2 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 Dot Number 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 3 to -1, and the item answer time is recoded from 2 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.
| Variables | Explanation | Values |
|---|---|---|
| pcdnstat1/2 | Status flag: outcome of test | 0=not started, 2=successfully completed, 3=abandoned or serial timeouts, 4=random responses |
| pcdndata1/2 | Data flag: is test data present? | 0=no, 1=yes |
| pcdntot1/2 | Total score for this test, out of 32. | 0 to 32 (integer values) |
| pcdnquan1/2 | Number of questions answered in the test | integer values up to 36 |
| pcdnhand1/2 | Handedness of twin (response to question in test introduction) | 1=right-handed, 2=left-handed, 0=unrecorded |
| pcdnstdt1/2 | Start date of the test [not in dataset] | Date values |
| pcdnsttm1/2 | Start time of the test [not in dataset] | Time values |
| pcdnendt1/2 | End date of the test [not in dataset] | Date values |
| pcdnentm1/2 | End time of the test [not in dataset] | Time values |
| pcdntmel1/2 | Total time elapsed during the test, in seconds | Integer values (number of seconds) |
| pcdnXXan1/2 (XX is the item number 01 to 36) |
Item response | 1=match, 2=no match, -1=timeout, -4=item crashed |
| pcdnXXsc1/2 (XX is the item number 05 to 36) |
Item score (not recorded for items 1 to 4) | 0=incorrect, 1=correct |
| pcdnXXat1/2 (XX is the item number 01 to 36) |
Answer time: length of time (in seconds) taken by the twin to respond to this item [not in dataset] | Decimal values, recorded to 3 decimal places (seconds, between 0 and 2) |
Test Items
There are 36 items in the main part of the test. 18 of these have numbers on the left and dots on the right, while 18 have dots on the left and numbers on the right. Every image is the same size, and appears in the same position on screen. In each image, the dots are arranged randomly (but the same images were used for all twins). Only items 5 to 36 contribute to the total score.
| Item no. | Left screen | Right screen | Match? | Image |
|---|---|---|---|---|
| 1 | number 1 | 1 dot | Yes |  |
| 2 | 7 dots | number 3 | No |  |
| 3 | 1 dot | number 1 | Yes |  |
| 4 | number 8 | 4 dots | No |  |
| 5 | 5 dots | number 5 | Yes |  |
| 6 | 9 dots | number 7 | No |  |
| 7 | number 4 | 4 dots | Yes |  |
| 8 | number 6 | 5 dots | No |  |
| 9 | 8 dots | number 9 | No |  |
| 10 | 7 dots | number 5 | No |  |
| 11 | number 6 | 6 dots | Yes |  |
| 12 | number 2 | 2 dots | Yes |  |
| 13 | number 7 | 9 dots | No |  |
| 14 | 6 dots | number 5 | No |  |
| 15 | 4 dots | number 4 | Yes |  |
| 16 | number 9 | 9 dots | Yes |  |
| 17 | 3 dots | number 2 | No |  |
| 18 | number 8 | 8 dots | Yes |  |
| 19 | number 5 | 6 dots | No |  |
| 20 | 2 dots | number 4 | No |  |
| 21 | 7 dots | number 7 | Yes |  |
| 22 | number 6 | 4 dots | No |  |
| 23 | number 3 | 3 dots | Yes |  |
| 24 | number 5 | 7 dots | No |  |
| 25 | 2 dots | number 2 | Yes |  |
| 26 | number 9 | 8 dots | No |  |
| 27 | 4 dots | number 6 | No |  |
| 28 | 8 dots | number 8 | Yes |  |
| 29 | number 2 | 3 dots | No |  |
| 30 | 5 dots | number 6 | No |  |
| 31 | 3 dots | number 3 | Yes |  |
| 32 | 9 dots | number 9 | Yes |  |
| 33 | number 5 | 5 dots | Yes |  |
| 34 | number 4 | 2 dots | No |  |
| 35 | number 7 | 7 dots | Yes |  |
| 36 | 6 dots | number 6 | Yes |  |