Software metrics lecture 4 Usability metrics

USABILITY METRICS
FAIZ UL HAQUE ZEYA

• Creating user-friendly interfaces is no longer optional,
it's essential. But how do we measure and define that
user-friendliness? Through usability metrics, the
quantifiable measures that help us understand how
effectively, efficiently, and satisfyingly users interact with
our products.

• Before choosing the right usability metrics for your
business, you first need to understand the different
measurable elements of usability. They include:
Effectiveness: Evaluate if users can achieve their goals
using your product.
Efficiency: Considers the resources that are expended by
your users in order to reach their goals.
Satisfaction: Measures how happy or satisfied your users
are after their interaction with your product.

Effectiveness Metrics
•Task Completion Rate: Measures the percentage of users who
successfully complete a given task.
•Error Rate: Measures the number of errors users make while
completing tasks.
•Time on Task: Measures the average time it takes users to
complete tasks.
Effectiveness Metrics

Task Success Rate or Task Completion Rate
• Task Success Rate or Task Completion Rate is a metric that measures the
percentage of users who successfully complete a specific task or set of tasks on a
website or application. It is commonly used to measure the effectiveness and
usability of a website or application, as well as user engagement and satisfaction. A
high task success rate generally indicates that a website or application is easy to
use and navigate, while a low task success rate may indicate that users are
struggling to complete certain tasks and may need to be redesigned or improved.
The formula for calculating task success rate is:
• Task success rate = (Number of successful task completions / Total number of
task attempts) x 100
• “Number of successful task completions” is the number of times users successfully
completed the task or set of tasks.
• “Total number of task attempts” is the total number of times users attempted to
complete the task or set of tasks.

Efficiency Metrics
 Time on Task: As mentioned in Effectiveness metrics.
 Number of Steps: Measures the average number of steps users take to complete tasks.
• System Response Time: Measures the time it takes for the system to respond to user actions

Satisfaction metrics
 System Usability Scale (SUS): A standardized questionnaire that measures overall user
satisfaction.
 Post-Task Surveys: Surveys given to users after completing tasks to gather feedback on specific
aspects of the experience.
• Heatmaps and Session Recordings: Visualizations of user interactions that reveal areas of
confusion or frustration

Fail rate
• Fail rate = (Number of failed tasks / total number of
assigned tasks) x 100
• If a task requires users to enter information that is
impossible to provide, this would be considered a ‘fail’ in
your usability metrics. You’ll recognize this one if you’ve ever
been asked to fill in a digital form with a required field that
doesn't permit the correct input, e.g. being asked to provide
a phone number in a text-only box.

Time on screen
• Time on screen measures how long a user spends on a particular
screen. Users spending a long time on a screen is an indicator they
can't find what they’re looking for (except for blog posts or pages with
readable content where the user might naturally spend more time). If
you review the time on screen along with metrics like misclick rate,
you can spot issues with the interface, labels, or layout of the page.
• How to measure time on screen
• Time on screen is usually calculated by your testing platform. It
records the amount of time your user spends on the same screen
before moving to a different one. However, if you’re doing this in
person, you can calculate it using a stopwatch or clock.

• The term “misclick” refers to an unintended or erroneous
click of a computer mouse or other input device, usually
resulting in a wrong action or result12
. For example, in a
game, if a player accidentally clicks on the wrong target, it’s
referred to as a "misclick"3
. Similarly, if you accidentally
select the wrong option on a menu on a computer, that’s
also considered a "misclick". It’s a common term used in
computing and gaming contexts

• Misclicks can occur due to a variety of reasons:
1.Unsteady Hand: An unsteady hand can cause the mouse to move
slightly, leading to a misclick.
2.Small Screen Size: On devices with small screens, the close proximity
of buttons and links can increase the likelihood of misclicks.
3.Lack of Attention: Not paying full attention to the task at hand can
result in misclicks.
4.Hardware Issues: Problems with the mouse or touchpad hardware,
such as a faulty button, can cause misclicks.
5.Speed of Action: Moving the mouse quickly or performing actions
rapidly can sometimes lead to misclicks.

Misclick rate
• The misclick rate is the average number of misclicks outside the hotspots or clickable
areas of your product. This usually happens when your user finds your platform
unintuitive or is expecting it to act similarly to other websites.
• According to Jakob's Law, “users spend most of their time on other websites”, so they
expect yours to function like the ones they already know. If it doesn’t, this can cause
usability issues. Review the misclick rate along with a detailed click heatmap to see
exactly where your users are clicking, and adjust your design accordingly to clarify.
• How to measure misclick rate
• To calculate your product’s misclick rate, you need to divide the number of misclicks
by the total number of clicks and multiply it by 100.
• Misclick rate = (Number of user misclicks / total number of user clicks) x 100
• For example, if a user made 15 clicks during the test and three were misclicks, your
misclick rate will be 20%.

1.I think that I would like to use this system frequently.
2.I found the system unnecessarily complex.
3.I thought the system was easy to use.
4.I think that I would need the support of a technical person to be able to use this
system.
5.I found the various functions in this system were well integrated.
6.I thought there was too much inconsistency in this system.
7.I would imagine that most people would learn to use this system very quickly.
8.I found the system very cumbersome to use.
9.I felt very confident using the system.
10.
I needed to learn a lot of special things before I could get going with this system.

Net Promoter Score (NPS)
• NPS stands for Net Promoter Score, which is a common
metric used in customer experience programs. An NPS score
measures customer loyalty by looking at their likelihood of
recommending a given business.
• Your NPS score is measured with a single-question survey
and reported with a number ranging from -100 to +100,
where a higher score is desirable.

• NPS measures customer perception based on one simple
question:
• “How likely is it that you would recommend
[Organization X/Product Y/Service Z] to a friend or
colleague?”

• Respondents give a rating between 0 (not at all likely) and
10 (extremely likely) and, depending on their response,
customers fall into one of 3 categories to establish an NPS
score:
• Promoters respond with a score of 9 or 10 and are typically
loyal and enthusiastic customers.
• Passives respond with a score of 7 or 8. They are satisfied
with your service but not happy enough to be considered
promoters.
• Detractors respond with a score of 0 to 6. These are
unhappy customers who are unlikely to buy from you again,
and may even discourage others from buying from you.

Click-through Rate (CTR)
• Click-through rate (CTR) is a metric used in online advertising to
measure the effectiveness of an ad campaign. It’s the percentage of
individuals viewing a web page who view and then click on a specific
advertisement that appears on that page1
.
• The formula to calculate CTR is:
• For example, if an online advertisement has been clicked on 200 times
after being served 50,000 times, the click-through rate would be 0.4%
= [(200 / 50,000) x 100]

Bounce Rate
• Bounce Rate is a term used in web traffic analysis. It represents the
percentage of visitors who enter the site and then leave (“bounce”) rather
than continuing to view other pages within the same site12
.
• Bounce Rate is calculated as follows:
• Bounce Rate=Total One-page Visits/Total Entrance Visits
×100
• A high Bounce Rate generally indicates that site entrance pages aren’t
relevant to your visitors. The more compelling your landing pages, the more
visitors will stay on your site and convert2
.
• The “average” Bounce Rate can vary based on industry and the source of
traffic. For example, ecommerce sites might have a Bounce Rate between 20-
45%, while blogs could have a Bounce Rate as high as 90%1
.

Eye tracking metrics.
Eye-tracking metrics are measurements that provide insights into how a user visually interacts with a
system or environment. Here are some of the most common eye-tracking metrics:
1.Fixations and Gaze Points: Fixations are periods where the eyes are locked towards an object,
indicating visual attention. Gaze points show what the eyes are looking at1
.
2.Heatmaps: Heatmaps are visualizations that show the general distribution of gaze points, typically
displayed as a color gradient overlay on the presented image or stimulus1
.
3.Areas of Interest (AOI): AOIs are predefined regions in the visual field that are of particular interest
in the analysis1
.
4.Time to First Fixation: This is the time it takes for the first fixation to occur on a specific AOI1
.
5.Dwell Time: Also known as Time Spent, this is the total time spent fixating or gazing at a particular area1
.
6.Fixation Sequences: This refers to the order in which different AOIs are fixated1
.
7.Revisits: This metric counts the number of times a user returns to an AOI after initially leaving it1
.
8.First Fixation Duration: This is the duration of the first fixation on an AOI1
.
9.Average Fixation Duration: This is the average duration of all fixations1
.
These metrics can provide valuable insights into user behavior, attention, and engagement, and are widely
used in fields like usability testing, market research, and psychology123
.

Scroll depth
Scroll Depth is a measurement of how far a user scrolls on a page. It’s typically measured as a
percentage of the total page content. For example, if a user were to scroll halfway down a page
and then leave, that user’s page session would have a scroll depth of 50%1
.
Scroll Depth is important because it gives us an idea of how far a user got into a page or a piece
of content before leaving. That’s information we can use to analyze the effectiveness of our pages1
.
There are tools like Google Analytics plugin that let you measure how far users are scrolling.
It monitors the 25%, 50%, 75%, and 100% scroll points, sending a Google Analytics Event for
each one. You can also track when specific elements on the page are scrolled into view2
.
What qualifies as a good scroll depth is dependent on the content you have on the page. There is no
universal scroll depth benchmark1
. For instance, on a company homepage with a large CTA above the
fold, a low scroll depth such as 25% is a good thing, as long as it’s paired with a low bounce rate. It indicates
that users are landing on the site and clicking on the CTA more or less immediately. On the other hand,
in a piece of long-form content, an average scroll depth of 25% would be very disappointing — that would
mean that very few visitors are actually reaching the end of the content1
.

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