A laboratory study, or a lab study for short, is a study that is conducted in a controlled environment. Unlike a field study that is conducted in the environment where the system is intended to be used, a usability lab study is conducted in a quiet office space or a usability lab. You prepare a set of equipment, invite study participants to the controlled environment, let them perform tasks to measure usability metrics, and analyze the data to inform the usability a software system.
An image of a usability lab. Source: Preece et al. Interaction Design: Beyond Human-Computer Interaction, p.476
The term "controlled" suggests that the study is more immune to the influence of confounds—factors that could unintentionally but systematically influence the usability measurements. Conducting a usability study in a lab setting allows you to control potential confounding factors such as device characteristics (e.g., mobile vs desktop computer, input device variability) and the physical environment (e.g., noise, lighting). Note that, in a controlled experiment, you should control not only devices and the environment, but you may also decide to control other things like age group, expertise in the given task, and disabilities.
A lab-based usability study can be categorized into two types: an observational study or an experiment. A designer performs an observational study when they collect data in a way that does not directly interfere with how the data arise. For a usability study conducted in the lab, you'd prepare (i) a single design of a system's user interface and (ii) a set of tasks that a participant can perform. Then, you simply observe how people use the system to perform the tasks and assess facets of usability (e.g., effectiveness, efficiency). In general, observational studies can provide evidence of a naturally occurring association between two variables (e.g., system's interface design and its effectiveness), but they cannot show a causal relationship.
Designers could conduct an experiment to quantitatively assess the causal relationship between the change in the design and usability of the system. There will be an independent variable (also known as a factor) which you can adjust. Usually, the independent variable is the design of the system in a usability study; you prepare design A and design B of a system's user interface. Participants are asked to perform a set of tasks using one of the designs, then the evaluator measures usability metrics like task completion time and error rate. These measured variables are called dependent variables or response variables. Finally, you assess if there is a difference in what you measured between design A and design B. We will talk more about an experiment in the future modules (16. Experiments and 17. Designing Experiments ).
Whether it is an observational study or an experiment, the high-level study procedure is similar. Performing a lab study involves:
Planning is the phase that requires most effort. In this phase, you should do the following: