Normative data

Normative data for the SIPP=118
Normative data are available for the 16 facets and the five higher order domains of the SIPP-118. The normative data were derived from two groups:

1. Patients admitted to one of six treatment centres throughout the Netherlands, participating in the Study on Cost-Effectiveness of Personality Disorder TREatment (SCEPTRE). Of these patients, those with at least one personality disorder according to the DSM-IV axis-II criteria (as measured by the semi-structured SIDP-IV) are included in this patient norm group. (n=1483, with 65% female, mean age 33.2 (sd=9.6).
2. Individuals from the general population (n=478), as obtained from a general practitioner register in the South-West of the Netherlands, with 70% female, mean age 36.3 (sd=11.4).

Calculation of standardized t-scores of the SIPP-118 (SPSS syntax)

Interpretation T-scores
<30:       very low
30-39:     low
40-59:     mediate
60-69:     high
≥70:       very high

1. First, you look at the severity (thus lower scores) of the personality pathology in comparison with the normal population:
   
   • Inspect the domain (*) level. Any T-scores below 40 indicate impaired adaptive functioning, and any T-scores below 30 indicate severely impaired adaptive functioning.
   • Within the domains with T<40, the next step is to look at the facet level. Which specific facets account (particularly) for the low score at the higher-order domain level?
     
     
2. Second, you compare these dimensions (either domains or facets) with T-scores lower than 40, with the clinical population data. This provides a sense of the clinical relevance.
   
   • For example, if T=34 in comparison with normals, but T=41 in comparison with other patients, this indicates low to modest severity.
   • However, if T=28 in comparison with normals, and T=32 in comparison with other patients, this indicates (very) high severity.
     
     
3. Third, you look at the healthy aspect (thus higher scores) of the patient’s personality:
   
   • Follow the same hierarchical strategy as with the identification of pathology, but now you look at T-scores above 60 for strong capacities, and above 70 for very strong capacities. Do not use clinical population data to identify strong capacities, thus only normal population data.

(*) NB  These steps should be read as a recommendation instead of as the only right option; some clinicians prefer to start with interpreting the facet-level instead of taking the domain-level of starting-point.