, Volume 34, Issue 2, pp 195–205 | Cite as

Using Classification and Regression Trees (CART) to Identify Prescribing Thresholds for Cardiovascular Disease

  • Chris SchillingEmail author
  • Duncan Mortimer
  • Kim Dalziel
  • Emma Heeley
  • John Chalmers
  • Philip Clarke
Original Research Article


Background and Objective

Many guidelines for clinical decisions are hierarchical and nonlinear. Evaluating if these guidelines are used in practice requires methods that can identify such structures and thresholds. Classification and regression trees (CART) were used to analyse prescribing patterns of Australian general practitioners (GPs) for the primary prevention of cardiovascular disease (CVD). Our aim was to identify if GPs use absolute risk (AR) guidelines in favour of individual risk factors to inform their prescribing decisions of lipid-lowering medications.


We employed administrative prescribing information that is linked to patient-level data from a clinical assessment and patient survey (the AusHeart Study), and assessed prescribing of lipid-lowering medications over a 12-month period for patients (n = 1903) who were not using such medications prior to recruitment. CART models were developed to explain prescribing practice. Out-of-sample performance was evaluated using receiver operating characteristic (ROC) curves, and optimised via pruning.


We found that individual risk factors (low-density lipoprotein, diabetes, triglycerides and a history of CVD), GP-estimated rather than Framingham AR, and sociodemographic factors (household income, education) were the predominant drivers of GP prescribing. However, sociodemographic factors and some individual risk factors (triglycerides and CVD history) only become relevant for patients with a particular profile of other risk factors. The ROC area under the curve was 0.63 (95 % confidence interval [CI] 0.60–0.64).


There is little evidence that AR guidelines recommended by the National Heart Foundation and National Vascular Disease Prevention Alliance, or conditional individual risk eligibility guidelines from the Pharmaceutical Benefits Scheme, are adopted in prescribing practice. The hierarchy of conditional relationships between risk factors and socioeconomic factors identified by CART provides new insights into prescribing decisions. Overall, CART is a useful addition to the analyst’s toolkit when investigating healthcare decisions.


Absolute Risk Individual Risk Factor Pharmaceutical Benefit Scheme High Total Cholesterol National Heart Foundation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This work was supported by Monash University, the George Institute for Global Health, and the University of Melbourne.

Chris Schilling, Duncan Mortimer, Kim Dalziel, Emma Heeley, John Chalmers and Philip Clarke declare that they have no conflicts of interest.

Author contributions

CS, DM and KD conceptualized this report. All authors had input in developing the approach. CS produced multiple drafts. All authors provided input on the draft report and all read and approved the final report.


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Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  • Chris Schilling
    • 1
    Email author
  • Duncan Mortimer
    • 2
  • Kim Dalziel
    • 1
  • Emma Heeley
    • 3
  • John Chalmers
    • 3
  • Philip Clarke
    • 1
  1. 1.Centre for Health Policy, School of Population and Global HealthUniversity of MelbourneMelbourneAustralia
  2. 2.Centre for Health Economics, Monash Business SchoolMonash UniversityMelbourneAustralia
  3. 3.The George Institute for Global HealthThe University of Sydney and the Royal Prince Alfred HospitalSydneyAustralia

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