The test itself (in its paper-and-pencil form) consists of a single 'recording blank'. The front page of this is reserved for recording the respondent's personal data and performance results. There is also a practice example so that the respondent can become acquainted with the task. On the reverse side is the standardised test form in a landscape layout of 14 test lines with 47 characters in each line. Each character consists of a letter, 'd' or 'p' marked with one, two, three or four small dashes. The respondent is required to scan the lines and cross out all occurrences of the letter 'd' with two dashes while ignoring all other characters.
Two scoring keys are provided; one for identifying errors of omission (missing characters that should have been crossed out) and one for identifying errors of commission (crossing out characters that should not have been crossed out).
The test results in the following norm-referenced scores:
- Total Number of items processed (TN) is the sum of all items processed whether correctly or incorrectly. It is a highly reliable measure of processing speed.
- Percentage of Errors (E%) measures the qualitative aspects of performance. It represents the proportion of errors made across all items processed. The smaller the percentage of errors, the better the subject’s accuracy.
- Total number of items processed minus errors (TN-E) provides an indication of the implications of the combined speed and accuracy scores for attentional and inhibitory control.
Further qualitative evaluation can take account of:
- Concentration Performance (CP) is the number of correctly processed items minus errors of commission. This score cannot be distorted by such tendencies as the haphazard skipping over of sections of the test or crossing out all letters without discriminating among them. This therefore provides a check on distortion in response style.
- Fluctuation rate (FR) is indicated by the discrepancy between the line with the maximum number of items processed and the line with the minimum of items processed. Extremely high raw scores can suggest an inconsistency in work speed perhaps related to poor motivation.
The technical manual contains instructions for administration, scoring and interpretation as well as documenting statistical research to date and the extent to which the d2 test fulfils standard test criteria. Reliability (internal & test-retest) is high. Criterion, construct and predictive validity have been demonstrated in numerous research studies. Extensive norms according to age, sex and education are included.
Available in paper or electronically; the computerised version is normed separately.