Patrick Oladimeji

Number entry interfaces and their effects on error detection

A significant amount of interaction involves number entry. The purpose of any number entry interface is to accurately select or set a numeric value. There are two main styles of number entry interfaces found on medical devices: serial interfaces like the ubiquitous 12-key numeric keypad, and incremental interfaces that use a knob or a pair of keys to increase or decrease numbers. We report an experiment that investigates the effect of interface design on error detection in number entry. The initial findings show that the incremental interface produces more accurate inputs than the serial interface, and the magnitude of errors suggests that the incremental interface could reduce the death rate relative to the numeric keypad.

The benefits of formalising design guidelines: a case study on the predictability of drug infusion pumps

A demonstration is presented of how automated reasoning tools can be used to check the predictability of a user interface. Predictability concerns the ability of a user to determine the outcomes of their actions reliably. It is especially important in situations such as a hospital ward where medical devices are assumed to be reliable devices by their expert users (clinicians) who are frequently interrupted and need to quickly and accurately continue a task. There are several forms of predictability. A definition is considered where information is only inferred from the current perceptible output of the system. In this definition, the user is not required to remember the history of actions that led to the current state. Higher-order logic is used to specify predictability, and the Symbolic Analysis Laboratory is used to automatically verify predictability on real interactive number entry systems of two commercial drug infusion pumps—devices used in the healthcare domain to deliver fluids (e.g., medications, nutrients) into a patient’s body in controlled amounts. Areas of unpredictability are precisely identified with the analysis. Verified solutions that make an unpredictable system predictable are presented through design modifications and verified user strategies that mitigate against the identified issues.

A Performance Review of Number Entry Interfaces

Number entry is ubiquitous and there are several ways a number entry interface can be designed. Until recently, research has been focused mainly on one type of number entry interface: the numeric keypad. Various factors such as the range of values, and the space available for the design allows for several alternative interfaces to be used for number entry. In the design of medical devices such as those used for controlled drug delivery, accurate and timely entry of numbers are required in order to reduce any risk of harm to patients. This paper reviews five number entry interface styles and reports the result of an experiment conducted to evaluate the performance differences of the interfaces based on numbers used in infusion therapy in a hospital. The result shows a significant effect of interface style on speed and accuracy.

PVSio-web 2.0: Joining PVS to HCI

PVSio-web is a graphical environment for facilitating the design and evaluation of interactive (human-computer) systems. Using PVSio-web, one can generate and evaluate realistic interactive prototypes from formal models. PVSio-web has been successfully used over the last two years for analyzing commercial, safety-critical medical devices. It has been used to create training material for device developers and device users. It has also been used for medical device design, by both formal methods experts and non-technical end users.

Social network analysis and interactive device design analysis

What methods can we use to help understand why users adopt certain use strategies, and how can we evaluate designs to anticipate and perhaps positively modify how users are likely to behave? This paper proposes taking advantage of social network analysis (SNA) to identify features of interaction. There are plausible reasons why SNA should be relevant to interaction programming and design, but we also show that SNA has promise, identifies and explains interesting use phenomena, and can be used effectively on conventionally-programmed interactive devices. Social network analysis is a very rich field, practically and theoretically, and many further forms of application and analysis beyond the promising examples explored in this paper are possible.

Using Medical Device Logs for Improving Medical Device Design

User interfaces that employ the same display and buttons may look the same but can work very differently depending on exactly how they are implemented. In healthcare, it is critical that interfaces that look the same are the same. Hospitals typically have many types of visually similar infusion pumps, but with different software versions and variation between pump behavior, and this may lead to unexpected adverse events. For example, when entering drug doses into infusion pumps different results may arise when pushing identical sequences of buttons. These differences arise as a result of subtle implementation differences and may lead to large errors users do not notice. Previous work has explored different implementations of a 5-key interface for entering numbers using a new analysis technique, Differential Formal Analysis, where predictions relating to the distribution of errors in terms of the size of the error (out by 10, out by 100 and so on) can be made. The analysis described in the paper extends this work with models of use based on many hours of actual clinical use data. Specifically, we draw on 1,362 days of use of number entry systems, from 19 infusion pumps over a 3 year period in a UK hospital. The paper also suggests some improvements to medical device logs, which will help further evidence-based improvement to medical device safety.

Combining PVSio with Stateflow

An approach to integrating PVS executable specifications and Stateflow models is presented that uses web services to enable a seamless exchange of simulation events and data between PVS and Stateflow. Thus, it allows the wide range of applications developed in Stateflow to benefit from the rigor of PVS verification. The effectiveness of the approach is demonstrated on a medical device prototype, which consists of a user interface developed in PVS and a software controller implemented in Stateflow. Simulation on the prototype shows that simulation data produced is exchanged smoothly between in PVSio and Stateflow.

Triangulating empirical and analytic techniques for improving number entry user interfaces

Empirical methods and analytic methods have been used independently to analyse and improve number entry system designs. This paper identifies key differences in exploring number entry errors combining laboratory studies and analytic methods and discusses the implications of triangulating methods to more thoroughly analyse safety critical design. Additionally, a previously presented analytic method used to analyse number entry interfaces is generalised to analyse more types of number entry systems. This paper takes number entry to mean interactively entering a numeric value, as opposed to entering a numeric identifier such as a phone number or ISBN. Many applications of number entry are safety critical, and this paper is particularly motivated by user interfaces in healthcare, for instance for specifying drug~dosage.

Towards safer number entry in interactive medical systems

Number entry is prevalent in the use of many interactive medical systems and number entry interfaces vary in complexity. Currently, research on number entry is focused on the numeric keypad and its different layouts. There are alternatives to the numeric keypad in use in safety critical contexts such as hospitals. I have surveyed several number entry systems and propose properties that would help compare them. My research on this topic aims to understand the characteristics of the styles of these interfaces, focusing on their effects on number entry error, the severity of such errors and exploring possible design choices that can reduce or manage the errors. This research will uncover number entry interface design trade-offs that will help designers make informed decisions about the safety and dependability of number entry systems.

Unreliable numbers: error and harm induced by bad design can be reduced by better design

Number entry is a ubiquitous activity and is often performed in safety- and mission-critical procedures, such as healthcare, science, finance, aviation and in many other areas. We show that Monte Carlo methods can quickly and easily compare the reliability of different number entry systems. A surprising finding is that many common, widely used systems are defective, and induce unnecessary human error. We show that Monte Carlo methods enable designers to explore the implications of normal and unexpected operator behaviour, and to design systems to be more resilient to use error. We demonstrate novel designs with improved resilience, implying that the common problems identified and the errors they induce are avoidable.