Complexity in decisions involving multiple factors and variability in interpretation of data motivate the development of computerized techniques to assist humans in decision-making.^{1–3} Predictive models are used in medical practice, for example, for automating the discovery of drug treatment patterns in an electronic health record,^{4} improving patient safety via automated laboratory-based adverse event grading,^{5} prioritizing the national liver transplant ‘queue’ given the severity of disease,^{6} predicting the outcome of renal transplantation,^{7} guiding the treatment of hypercholesterolemia,^{8} making prognoses for patients undergoing certain procedures,^{9}
^{10} and estimating the success of assisted reproduction techniques.^{11} Numerous risk assessment tools for medical decision support are available on the web^{12–14} and are increasingly available for smart phones.^{15–17}

While many predictive models have been developed and validated on data from cohort studies, little attention has been paid to ensure the reliability of a prediction for an individual, which is critical for point-of-care decisions. Because the goal of predictive models is to estimate outcomes in new patients (who may or may not be similar to the patients used to develop the model), a critical challenge in prognostic research is to determine what evidence beyond validation is needed before practitioners can confidently apply a model to their patients.^{18} This is important to determine a patient's individual risk.^{19–21} As each model is constructed using different features, parameters, and samples, specific models may work best for certain subgroups of individuals. For example, many calculators and charts use the Framingham model to estimate cardiovascular disease (CVD) risk.^{8}
^{22–24} These models work well, but may underestimate the CVD risk in patients with diabetes.^{25}
illustrates a case in which a patient can get significantly different CVD risk scores from different online risk estimation calculators. This type of inconsistency provides another motivation for selecting an appropriate model.^{29}

| **Table 1**The same patient can get different risk scores from different online tools |

In order to obtain a patient-specific recommendation at the point of care, it is necessary that physicians interpret the information in the context of that patient. These scenarios are related to personalized medicine, which emphasizes the customization of healthcare.^{30}
^{31} In this research, we address the problem of selecting the most appropriate model for assessing the risk for a particular patient. We developed an algorithm for online model selection based on the CI of predictions so that clinicians can choose the model at the point of care for their patients, as illustrated in .

Our approach is purely data driven because it adapts to any ‘appropriate’ model that is available for assessing the risk of a patient without the need for external knowledge. The ‘appropriateness’ refers to the ability of the model to generate a narrow CI for the individualized prediction. The article is organized as follows: the following paragraphs present related work, the Methods section introduces the details of the proposed method, the Results section presents results on simulated and clinically related datasets, and the Discussion section discusses advantages and limitations.

A possible approach to determining the best model for a patient is to compare the patient with individuals in the study population used to build the model. However, it is non-trivial to gather datasets from every published study. The barriers are partly related to the laws and regulations on privacy and confidentiality.^{32} Therefore, we aimed at developing a new method to determine the most reliable predictive model for an individual from a candidate pool of models without requiring the availability of training datasets. Note that our motivation for selecting the appropriate model in a distributed environment is somewhat different from the one that motivates adaptive model selection. Adaptive model selection operates in a centralized environment and searches for an optimal subset of patterns from the entire training set to minimize certain loss functions.^{33}

The idea of data-driven model selection for medical decision support is related to dynamic switching and mixture models,^{34} which emphasize capturing the structural changes over time to adapt a predictive model. Fox *et al*^{35} proposed a method for learning and switching between an unknown number of dynamic modes with possibly varying state dimensions. Huang *et al*^{36} presented a segmentation approach that divided deterministic dynamics in a higher-dimensional space into segments of patterns. Siddiqui and Medioni^{37} developed an efficient and robust method of tracking human forearms by leveraging a state transition diagram, which adaptively selected the appropriate model for the current observation. Other methods were used in the context of wireless sensor networks in which the goal was to provide an effective way to reduce the communication effort while guaranteeing that user-specified accuracy requirements were met. For example, Le Borgne *et al*^{38} suggested a lightweight, online algorithm that allowed sensor nodes to determine autonomously a statistically good performing model among a set of candidate models.

However, most of the aforementioned methods describing real-world physical systems are not directly applicable to medical decision support because they rely on physical laws that are not applicable to medical decision-making. We propose a novel data-driven method to estimate the probability of the binary outcome for each new patient. In particular, based on patient characteristics, our method chooses the model that is most appropriate (ie, the one with the narrowest CI) from a set of candidate models and uses its predicted probability.