The Mississippi Scale for Civilian PTSD (CMS).

• Devised By: The Mississippi Scale for Civilian PTSD is a sub device of the Mississippi Scale for combat-related PTSD. The Mississippi Scale for combat-related PTSD was devised by Keane, T.M, Caddell, J.M, and Taylor, K.L. (1988). This reference is also used when referring to the CMS.

• Type of Instrument: The scale consists of 39 self-report items derived from the Diagnostic and Statistical Manual of Mental Disorders III-R criteria for PTSD. The first version of the Mississippi Scale contained 35 items, based on the unrevised DSM-III criteria for PTSD. The four added items (items 36 to 39) assess re-experiencing, psychogenic amnesia, hypervigilance, and increased arousal symptomatology (Lauterbach et al, 1997).

• Reliability:
  • Split-half / Cronbach's Alpha: Lauterbach et al (1997) found a coefficient alpha for the total questionnaire of .89, which is high. When investigating the alpha for the first and the second half of the questionnaire these authors found .79 and .81 respectively, thus deriving a split-half reliability r = .80. These correlations are high and suggest that the scale measures a single construct (PTSD) and that the scale is internally consistent.

    In other words, the scale can distinguish between persons who have and those who have not experienced some form of trauma, and between persons who have experienced different types of trauma.

    The original military and the civilian version of the Mississippi Scale are very similar, and contain parallel items. In the civilian version the wordings of eleven items have been changed from a military setting to a more general setting.

    Whilst high, the civilian version was found to be less internally consistent (a ~.89) than the military version (a ~.94). This could be more a reflection of the homogeneity of the military population.

     

  • Test-Retest Reliability: Keane et al (1988) calculated the test-retest reliability of the 35-item military version of the Mississippi scale with a 1-week interval and found a correlation of .97 (p <.0001). This finding supports the stability of the scale over brief periods.

   

  • Alternate Form Reliability: NA
  • Inter-rater Reliability: NA

   

• Validity:
  • Criterion Validity: In the Lauterbach et al (1997) studies higher scores on the civilian scale were related to having experienced a traumatic event. In both studies the group who had experienced some sort of trauma scored significantly higher on the measure (Study I: F(1,433) = 12.9, p <.0005; Study II: F(1,398) = 8.93, p <.003).

   

  • Content Validity: The CMS measures a single construct (presumably PTSD). However, there is much discusion and confusion regarding the degree to which the Mississippi measures just PTSD or PTSD and depression.

   

  • Construct Validity: Factor analysis to measure whether or not the items of the C-Mississippi Scale load onto different sub-scales indicates inconsistency in factor structure. Different studies found different sub-scales and factor structures. Thus, a validation of the construct of PTSD across groups is currently not advised by use of the CMS (Lauterbach et al, 1997).

    However, with respect to the military version, six sub-scales were found by Keane et al (1988):

    1. intrusive memories and depressive symptoms, nine items (r = .89)
    2. interpersonal adjustment problems, five items (r = .78)
    3. lability of affect and memory, 3 items (r = .64)
    4. ruminative features of PTSD, 3 items (r = .70)
    5. other interpersonal problems, 3 items (r = .46)
    6. sleep problems, 2 items (r = .50)

     

  • Convergent Validity: Lauterbach et al (1997) investigated correlations between two specific PTSD measures, the Purdue PTSD Questionnaire-Revised (PPTSD-R) and the Impact of Event Scale (IES).The CMS had a correlation of .52 (PPTSD-R) and .36 (IES). These correlations are in the low to moderate range. In a small sample (N=26) of 'generic' PTSD Devilly & Spence (1999) found the CMS to correlate with the PTSD Symptom Scale (.52), the Impact of Events Scale (.51), and the PTSD-Interview (DSM-III-R version; .69). However, consistently higher correlations were obtained with measures of negative affect such as the BDI (.64), Trait Anxiety (.65) and with measures of global distress such as the SCL-90-R (.75).

   

  • Discriminant Validity: In addition, they found correlations of .71 with the Beck Depression Inventory (BDI) and of .70 with the Trait version of the State-Trait Anxiety Inventory (STAI-T). These correlations are in the moderate to high range. All these tests were significant at p <.0001.

    These findings with respect to convergent and discriminant validity indicate that the CMS is more strongly related to measures of depression and anxiety than to other measures of PTSD, suggesting that the Civilian Scale measures general psychological distress or negative affect rather than specific PTSD symptomatology.

• Scoring Method: Each item is rated on a 5-point Likert scale, with items 2, 6, 11, 17, 19, 22, 24, 27, 30, and 34 scored in the reverse order (i.e. subtract their rating from 6). All the items are than added to obtain a total score on the scale.

• Norms:

  The norm groups have the following means and standard deviation measures:

  PTSD patients: 130, SD = 18

  Psychiatric patients: 86, SD = 26

  Normal controls: 76, SD = 18

  However, these are norms for the combat-related version of the Mississippi scale, since at this stage there are no norms available for the civilian version. In the Lauterbach et al (1997) study, subjects were psychology students, who scored a mean of 82.9 (SD = 16.3).

   

• References:

  Devilly, G.J. and Spence, S.H. (1999). The relative efficacy and treatment distress of EMDR and a cognitive-behavior trauma treatment protocol in the amelioration of posttraumatic stress disorder. Journal of Anxiety Disorders, 13, 131-157.

  Keane, T.M., Caddell, J.M., and Taylor, K.L. (1988). Mississippi scale for combat-related posttraumatic stress disorder: Three studies in reliability and validity. Journal of Consulting and Clinical Psychology, 56, 85-90.

  Lauterbach, D., Vrana, S., King, D.W., and King, L.A. (1997). Psychometric properties of the Civilian version of the Mississippi PTSC scale. Journal of Traumatic Stress, 10, 499-513.

See here for questionnaire availability

Above written by: Ms. Marjan Geertsema

Reviewed, edited and approved by: Dr. Grant J. Devilly