Casemix
Background
The primary objective of the New Zealand Mental Health Classification and Outcomes Study (CAOS) of 2003 was the development of the first version of a national casemix classification for specialist mental health services in New Zealand that built on the Australian MH-CASC project.
The CAOS study recommended that this first version casemix classification system be implemented into routine clinical practice, in order that routinely collected data be used to improve it.
Following on from the CAOS study, the Ministry of Health mandated collection of routine outcome measures, the Health of the Nation Outcome Scale (HoNOS) family initially, in New Zealand mental health services. A national programme, MH-SMART, was established in 2003 to assist District Health Boards (DHBs) in implementing the collection of these measures. HoNOS outcomes information has been collected in New Zealand mental health services routinely since July 2005.
With the implementation of the Programme for the Integration of Mental Health Data (PRIMHD) in July 2008, outcomes information now forms a mandatory part of the national mental health dataset.
To allow analysis of outcomes achieved by different mental health services, outcomes need to be casemix-adjusted to take account of the unique mix of service users at each DHB.
What is casemix?
Casemix is a way to group like ‘cases' or 'outcomes episodes' of mental health care so outcomes can be compared.
Casemix enables a better understanding of the real differences in service user outcomes achieved between differing services.
A casemix grouper will sort outcomes episodes into one of the 42 classes within the NZ-CAOS Casemix Classification.
Classes are grouped into one of seven branches for Adults or Child and Youth; for example, Adult Inpatient Complete, Adult Inpatient Ongoing, Adult Community.
Casemix in PRIMHD 2011
The Ministry of Health had several clear objectives in implementing PRIMHD, one of these was to include the ability to analyse outcomes information using casemix.
Te Pou completed a project in 2010 which developed and tested 13 business rules for episode building and casemix grouping using outcomes information collected for Te Pou’s Test Project. This casemix episode building process created 47,182 outcomes episodes (or matched pairs of collections), from an individual collection dataset of 118,493 collections from seven district health boards (DHBs) with mean improvements by class comparable to those reported by the CAOS study in 2003.
In late 2010, the Ministry of Health asked Te Pou to retest the feasibility of episode building and casemix grouping, this time using PRIMHD data.
The current project commenced in January 2011 and uses an extract of PRIMHD data to validate the business rules developed, and test whether casemix grouping is feasible using the PRIMHD dataset.
This work includes the following main components.
- Assessment and/or modification of existing business rules for building an outcomes episode dataset. Implementation and testing the results with PRIMHD data, initially 90,000 outcomes collections (those with the Outcomes Episode Identifier present).
- Identification of a process to build episodes without the use of the episode identifier. Implementing and testing the results of such a process and retesting with the episode set from the 90,000 initial outcomes collections.
- Incorporation of any rule changes or additions into the algorithm and completion of episode building with the entire PRIMHD outcomes collections database.
- Grouping episodes according to the New Zealand Mental Health casemix classification and comparison with results from NZ CAOS.
- Demonstrating the use of casemix adjusted outcomes information to allow quality improvement or benchmarking activity.
- Analysis of the resulting episodes in terms of their links with activity and investigating any predictive capacity of casemix.
The results of this project will help inform and progress the development of a casemix grouper in PRIMHD.
Casemix adjusting PRIMHD data will allow the Ministry of Health and DHB services at all levels to begin benchmarking or quality improvement initiatives based on comparable data.
NZ-CAOS Casemix Classification Tree
