Evidence-Based Design: Enhancing Your Decision-Making with the Power of Psychology and Heuristics

Raluca Angelescu
May 22, 2023
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Navigating the world of stakeholder engagement and decision-making can often feel like a daunting task. We, designers, are sometimes enticed to comfortably remain within our creativity sphere, cherishing our innovative solutions before layering in the supporting evidence for our decisions.

The complexity grows when we find ourselves engaged in smaller projects with scarce resources, when analytics tools seem out of reach, or when the number of survey responses leaves us wanting more. And then, there are those projects that don't quite take off, remain incomplete, or have to be shelved altogether. How you might ask, do we provide evidence for our design decisions in such scenarios? I have a few insights in this article.

But let's start with the happy path, shall we? That almost utopian project where we have access to users, gain valuable insights, and have plenty of analytic tools. In such an optimal situation, the evidence supporting our design decisions might appear in several forms:

  1. User quotes and data gathered from interviews or field studies offer rich, qualitative insights.
  2. Information derived from quantitative studies provides measurable and statistically significant data.
  3. Data extracted from analytics equips us with real-time and historical user behavior patterns.

But what if the scenario is not that favorable? How do we find evidence, then? Let me walk you through some of the ways.

Mental Models

Let's talk about mental models, a significant part of design strategy that we often overlook. The truth is, we don't always need to reinvent the wheel. In fact, there's substantial value in constructing and making design decisions based on existing, successful models.

Imagine if every door Designer insisted on making each door utterly unique. You'd find yourself struggling every time you faced a door, because it would operate differently. Now, apply this thought to product design. As a user, you don't want to learn how to navigate a new app from scratch every time; you'd rather rely on your previous experiences.

Take Instagram, TikTok, and Twitter for instance. If you compare their profile pages, you'll find striking similarities - about 95% similarity to be exact. The reason behind this is clear: these apps don't want users spending the majority of their time relearning how to navigate, say, a profile section. They want you to jump right in and enjoy the app.

Utilizing familiar mental models in design can be incredibly powerful and efficient. Unless there's a compelling reason to innovate, building upon what already exists and what users are familiar with is often the wisest approach.

assorted-color lockers


Given their training, designers often adopt a 'user-first' approach, which can sometimes skew towards being 'user-only'. However, it's equally important to keep the business perspective in mind and the competitive landscape.

Incorporating competitive insights into design decisions doesn't imply imitation or replication. Instead, it involves a thoughtful analysis of why a competitor made certain decisions, followed by a conscious decision on your part to tread a similar path or innovate. This could be because the competitor's approach aligns with well-established design principles, user expectations, or business needs.

By looking into and understanding the competitive landscape, you can get valuable insights into what works and what doesn't within the industry or the specific market segment. This holistic approach to decision-making ensures that the end product not only serves the user well but also aligns with the broader business strategy and industry standards.

person in green and black shorts riding on black and red bicycle

Psychology Rules

As we become more seasoned in the design process, it's not uncommon to rely on our instincts or make decisions based on what "feels" right. However, it's important to remember that these seemingly intuitive choices are often deeply rooted in the scientific understanding of design and psychology.

Design principles such as the Law of Proximity, Fitts's Law, and the Gestalt principles aren't just abstract theories; they provide a reliable framework for predicting user behavior and tailoring our designs to match. These principles are the result of extensive research and observation, underpinning what we might perceive as an intuitive understanding or "common sense."

When we use these principles as the rationale behind our design decisions, it not only strengthens our case but also demonstrates our expertise and commitment to the craft. By showing that our design decisions are grounded in such principles, we also show our dedication to creating user-friendly and impactful designs. This awareness and understanding of design psychology can become a valuable asset, enhancing the credibility of our decisions and our overall design approach.

a neon display of a man's head and brain

Heuristics Principles

Another effective and professional approach to substantiating your design decisions lies in adhering to heuristic principles. These 'rules of thumb' form the bedrock of good design, guiding us in crafting user interfaces that are not only intuitive and user-friendly but also impactful.

These principles were popularized by Jakob Nielsen, a renowned usability consultant, and continue to be a mainstay in the designers' toolbox even today. The strength of heuristic principles is in their broad applicability across different design contexts. Validated through extensive user interactions across diverse digital platforms, they have certainly stood the test of time.

The term was popularized by Jakob Nielsen, a renowned usability consultant, and Designers refer to it today. The power of heuristic principles lies in their universal applicability. These guidelines have also stood the test of time and have been validated through countless user interactions across various digital platforms. They consider the inherent ways in which users interact with and understand interfaces, thereby increasing the likelihood of a product's success.

Take, for example, the principle of Consistency and Standards. This heuristic principle talks about the importance of maintaining uniformity in design to meet users' expectations based on their previous experiences. For instance, hyperlinks are traditionally underlined and blue in color. By maintaining this standard in a web design, we eliminate potential confusion for the user, making navigation more seamless. And this is just one example.

low angle photo of escalator

Navigating the labyrinth of decision-making is undeniably a challenging task, but armed with the right tools and mindset, it becomes more manageable and meaningful. As designers, we are not just creators but also problem-solvers. We have the unique opportunity to harmonize user needs, business objectives, and industry standards into a cohesive, effective design.

Understanding and utilizing mental models, competition analysis, principles rooted in psychology, and heuristic principles provide a solid foundation for our design decisions. They offer the evidence needed to substantiate our choices and advocate for our design, regardless of the project size, resources, or the stages of its lifecycle.
With these principles in mind, we can navigate any challenge that comes our way, ensuring that our design decisions are always informed, justified, and poised for success.

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