Major Depression Inventory (MDI)

Background
The most commonly utilized measures of depression were created prior to the release of the Diagnostic and Statistical Manual of Mental Disorders III (DSM-III) in 1980. Therefore, items on these tests may not be optimal. Consequently, new tools were formulated such as the Major Depression Inventory (MDI) (Cuijpers et. al., 2007). The MDI is a self-rated tool that has a dual function; it can be either a diagnostic instrument that aids in assessing the presence of DSM-IV major depression, or a measure of the degree of depression severity (Bech et. al., 2015).
It was developed by Professor Per Bach and associates in collaboration with the Psychiatric Research Unit of the Danish World Health Organization Collaborative Centre for Mental Health (Konstantinidis et al., 2011 & Psychiatric Times, 2013). It consists of 12 items; Items 8 and 10 involve two sub-items; a and b, all scored on a frequency response scale ranging from “none of the time” (zero) to “all of the time” (five), and is answered in the context of the last 2 weeks. Functionally, it only contains 10 items as only the highest score of either a or b are counted in both Item 8 and 10 (Bech et. al., 2015, Konstantinidis et. al., 2011, & Bech et. al., 2001).

Scoring
Using the MDI as measure of depression severity: total score of ten items calculated by adding together 10 scores. The total score range is 0-50. 0-20 indicates depression does not exist or its existence is doubtful, 21-25 indicates mild depression, 26-30 indicates moderate depression, and 31-50 indicates severe depression.

Using the MDI as a diagnostic tool: algorithm for DSM-IV diagnosis of major depression; Items 4 and 5 are combined and only the highest answer of the two is considered. The presence of at least 5 of 9 symptoms indicates diagnosis of major depression. Item 1 or 2 must be among the 5 or more symptoms. The clinical range incorporates Items 1 to 3 occurring most of the time or all of the time, and all other symptoms occurring either slightly more than half of the time, most of the time or all of the time. If 5 or more symptoms are in this range, a diagnosis of major depression is supported (Bech et. al., 2015, Konstantinidis et. al., 2011, & Bech, 2011).

Psychometric Properties
Research findings suggest that the MDI possesses good reliability, validity, sensitivity and specificity (Cuijpesr, 2007). Cuijpers and associates (2007) found that the test had good reliability, a substantial correlation with another measure of depressive symptoms, and acceptable specificity and sensitivity. Also, Forsell (2003) found that the MDI has high internal consistency. Furthermore, Olsen and colleagues (2003) found that the tool demonstrated adequate internal and external validity as a measure of depression severity.
In regards to differential diagnosis, the levels of sensitivity and specificity that the MDI has demonstrated across multiple studies indicates that the MDI has the ability to identify individuals who have depression and to identify those who do not. Hence, this test may assist in the process of differential diagnosis (Cuijpers, et. al., 2007).

Strengths of the MDI include: being able to utilize it as a continuous scale indicating level of depression symptoms, and as a method of acquiring an indication of the existence of major depression, the fact that it appears to be a reliable tool for evaluating depression, and that it is brief in nature (Cuijpers et. al., 2007).

Some weaknesses of the MDI: the fact that whilst sensitivity and specificity of the diagnostic algorithm have been found to be acceptable in clinical populations, in general populations sensitivity and specificity have been found to be low (Amris et. al., 2016). Also, further research on the MDI is needed, and the tool was based on the DSM-IV, however this has been superseded by the DSM-5, thus the tool may not be representative of the new DSM.

Some evidence exists to suggest the MDI is reliable and valid across many countries and cultures and across genders (Cuijpers, 2007, Olsen et. al., 2003, Fountoulakis, et. al., 2003, & Konstantinidis et. al., 2011).