Method

In developing a dimensional scheme our aim was to use a small number of numerical measures that would usefully extend the existing bipolar disorder diagnostic schemes – specifically, to retain the key information required to make diagnoses whilst maximizing the richness of the additional descriptive information and minimizing the problems inherent in the categorical approach. In using the current classifications for diagnosis of individuals within the Bipolar spectrum, the following key issues are considered within the decision-making process:

1) The presence and severity of manic syndromes.

2) The presence and severity of depressive syndromes.

3) The presence of psychotic symptoms and the balance of mood and psychotic symptomatology.

4) The mood congruence of psychotic symptoms and the temporal relationship between affective and psychotic symptomatology.

In order to capture information relating to the 4 key issues above, we, therefore, chose to use 4 dimensions, one for each issue. Each dimension was set up to provide an ordered (not necessarily linear) measure of the relevant lifetime experience of psychopathology for the individual such that those scoring higher on the scale would have experienced more clinically important and convincing psychopathology – typically a mix of severity and frequency/duration. Ranges and anchor points in the scales were initially decided after discussion by the senior investigators and informed by (a) the current concepts of severity and type of mood syndrome recognized within DSMIV and ICD10, (b) the literature regarding severity of episodes [8-10], and (c) our own experience in clinical work and research with patients with bipolar spectrum disorders. We undertook an iterative process in which we initially agreed scale definitions and rating guidelines, piloted their use on sets of cases and modified the scale and guidelines to improve utility and reliability. The scale – the Bipolar Affective Disorders Dimension Scale, BADDS – has been under development by our group since 1996 and has gone through several iterations. We describe the most recent iteration, Version 3.0 which has been used by our group and collaborators since 1999. All individuals who were assessed with Bipolar Affective Disorders Dimension Scale as part of the diagnostic assessment provided written informed consent to participate in family-genetic studies of mood disorder and our protocols received approval from relevant ethical review committees.

BADDS (the Bipolar Affective Disorders Dimension) comprises four dimensions that provide a quantitative measure of lifetime experience of psychopathology in each of four domains: Manic-like episodes (the Mania dimension, M), Depression-like episodes (the Depression dimension, D), Psychotic symptomatology (the Psychosis dimension, P) and the relationship (in both congruence of content and in timing) between psychotic features (if present) and mood episodes (the Incongruence dimension, I) (see supporting material, appendix A for the BADDS rating guidelines). Each dimension provides a composite measure that takes account of both severity and frequency of relevant psychopathology and is rated using integers in the range 0 to 100, inclusive. As with conventional lifetime best-estimate categorical diagnosis, the dimensional ratings are made on the basis of all available information – which typically would include semi-structured lifetime psychiatric interview and review of psychiatric case notes. The criteria used for bipolar spectrum diagnoses is similar within DSMIV and ICD10. We have used ICD10 as the primary source for episode definitions because it provides a clearer differentiation of severity for depressive episodes. Basic background information and general rating guidelines are provided in pages 1 and 2 of the BADDS rating guidelines (see Appendix A). The specific characteristics of each dimension are described below.

Mania dimension, M

The severity of the lifetime worst (ie. most severe) episode of manic spectrum psychopathology identifies a range of scores on the M dimension to be considered (see table 2 and the rating guidelines for the scale: Appendix A). The lifetime "amount" of manic spectrum psychopathology experienced then determines the score within the range according to clear guidelines that attach weight to the number and severity of episodes but allow sufficient flexibility that ratings can take account of other factors where appropriate (such as length of episodes).

Once the range for rating has been decided by considering the severity of the worst episode, the score is determined by starting at the lowest score in the range and adding 2 points for each additional episode of equal severity, up to, but not exceeding, the maximum score in the range. Thus, an individual who has experienced 7 episodes of incapacitating mania would be rated M = 92 (the range is 80–100 with 12 points being added to the initial 80 because there have been 6 incapacitating episodes over and above the worst episode that identified the range). Similarly an individual who has experienced 3 episodes of hypomania would be rated as M = 44. An individual who has experienced 50 near-hypomanic episodes (ie. episodes that closely approach, but do not meet, criteria for hypomania) would be rated as M = 39. For individuals who (as is common) have also experienced episodes of lower severity than the worst ever episode, points can be added – but with a substantially lower weighting than for additional episodes at the same severity. Thus, an individual who has experienced 2 episodes of mania (none incapacitating) and 10 episodes of hypomania would receive a rating of M = 67 (the range is 60–79; the worst episode of mania provides a starting score of 60 to which is added 2 points for the second manic episode and 5 points for the 10 hypomanic episodes). An individual who has experienced 2 episodes of mania (none incapacitating) and 10 episodes of near-hypomania would receive a rating of M = 62 or 63 depending upon the judgement of the rater as to the importance of the near-hypomanic episodes (the range is 60–79; the worst episode of mania provides a starting score of 60 to which is added 2 points for the second manic episode and up to one point for the 10 sub-hypomanic episodes).

Depression dimension, D

The principles for this dimension follow closely those for the M dimension. The severity of the lifetime worst (ie. most severe) episode of depression spectrum psychopathology identifies a range of scores on the D dimension to be considered (see table 3 and the rating guidelines for the scale: Appendix A). The lifetime "amount" of depression spectrum psychopathology experienced then determines the score within the range according to clear guidelines that attach weight to the number and severity of episodes and allows sufficient flexibility that ratings can take account of other factors where appropriate (such as length of episodes).

Once the range for rating has been specified by considering the severity of the worst episode, the score is determined by adding 1 point for each additional episode of equal severity for the mild and moderate depression ranges (each of which spans 10 points) and 2 points for each additional episode of equal severity for the other ranges (each of which spans 20 points). Thus, an individual who has experienced 11 or more episodes of incapacitating depression would be rated D = 100 (the range is 80–100 with 20 points being added to the initial 80 because there have been 10 or more incapacitating episodes over and above the worst episode that identified the range). An individual who has experienced 3 episodes of moderate depression would be rated as D = 52 (the range is 50–59 with 2 points being added to the initial 50 because there have been 2 episodes over and above the worst episode that identified the range). As with the M dimension, for individuals who have also experienced episodes of lower severity than the worst ever episode, points can be added but with a substantially lower weighting than for additional episodes at the same severity.

Psychosis dimension, P

This dimension is concerned with lifetime occurrence of psychotic and near-psychotic features. It provides a measure of the proportion of functional psychotic illness in which psychotic symptoms (delusions, hallucinations, positive formal thought disorder, catatonia or grossly disorganized behaviour) have been present. The rating takes account of both the number and duration of episodes with and without psychotic features (see table 4 and the rating guidelines for the scale: Appendix A). Near-psychotic schizotypal features (specifically the following DSMIV schizotypal items: ideas of reference; odd beliefs or magical thinking that influences behaviour and is inconsistent with sub-cultural norms; unusual perceptual experiences including bodily illusions; odd thinking and speech; suspiciousness or paranoid ideation; behaviour or appearance that is odd eccentric or peculiar), in the absence of clear-cut psychotic features, can be rated in the lowest range of the dimension if there have been no clear-cut psychotic features.

Rating of 0 and 1 have specific definitions. The severity and amount of relevant psychopathology are rated within the ranges 2–9 (for near-psychotic features), 10–20 (for relatively brief single or multiple psychotic features) and 21–100 (for individuals having multiple episodes where psychotic symptoms are a prominent feature). Thus, an individual for whom psychotic features have been present and prominent in each episode of illness would be rated P = 100 (whether this is a single episode or 20 episodes). An individual for whom psychotic features have been present and prominent in one third of episodes of illness would be rated P = 33. An individual for whom multiple psychotic features have been present but were brief and non-prominent would be rated P = 20. An individual who has never experienced clear-cut psychotic features but has had frequent near-psychotic features would be rated P = 9, and such a person who has had only occasional near-psychotic features would be rated P = 2.

Incongruence dimension, I

This dimension is the most complex and provides lifetime information about the relationship between psychotic and affective psychopathology, specifically in three areas: (a) the mood congruence of any psychotic features that occur, (b) the occurrence of specific symptoms that have special diagnostic weight in the diagnosis of schizophrenia and schizoaffective disorder within current operational classifications (which we denote for convenience, the "S set": thought echo, insertion, withdrawal or broadcasting; passivity experiences; hallucinatory voices giving running commentary, discussing subject in third person or originating in some part of the body; bizarre delusions; catatonia), and (c) the temporal relationship between mood and psychotic psychopathology (see table 5 and the rating guidelines for the scale: Appendix A). The dimension is rated only if the P dimension has been rated at P > 9 (ie. occurrence of definite psychotic symptoms at some time during lifetime); otherwise, it is left blank.

Thus, an individual who has psychotic features only during affective episodes and for whom the psychotic symptoms are mainly, but not exclusively mood congruent,