Biases

Biases or cognitive biases are irrational judgments or subconscious inferences made from the data available to us. 

In testing, biases have the effect of causing you to miss or focus too much on specific behavior, processes, or data. We use our knowledge of biases in testing to improve our strategies by using biases to our advantage. 

Biases can be used as a heuristic, for example, in learning about our team's desires and expectations. Ignoring biases can affect your perception of the product you're testing and the quality of your testing. 

It may lead to gaps in your testing, and bugs could slip through. You need to be aware when you're using a bias deliberately that there is potential information you're missing out on, and you need to carry out additional activities to balance it out. Being conscious of biases allows us to attempt to prevent them from negatively impacting our testing. 

We could also use biases to focus or zone in on specific testing activities. Example biases: Inattentional blindness, when you miss something in one area of the application because you're focused on another point. 

Confirmation bias, when you promote data that proves your point of view and ignore data that challenges it. Observational bias. So the expectancy what that what we see, what we want to see, or in testing, create tests to return what we want to see. 
It's normal for us to have biases - a tendency to lean one way or another, which we may or (more commonly) may not be aware of.  This can affect the judgements and decisions we make in an unreasonable or unfair way.

Say, for example, you prefer the colour blue over red.  When given the choice to accept one of two people into your team, you may choose the person who is wearing blue over the person who is wearing red, because you like blue better and subconsciously take that to mean the person wearing blue is the better choice.  In reality, the two things have no relation, so it would be unreasonable to make your decision based on this.

The difficulty is that if you're not aware of this bias, it's very difficult to counteract.  That's why biases can be dangerous, and it's important that we make a conscious effort to try and identify them, and remain open to other, more logical factors to base our judgements and decisions on.

In software production, biases can cause us to miss potential issues or risks, or make decisions which do not support the quality of the product.  If you have a particular stance on something but you don't know why, or notice a pattern in your behaviour that can't be reasonably explained, there may be biases at play.  Take it as an opportunity to check in with yourself and review which facts are and are not relevant.
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