How to Avoid Selection Bias

How to Avoid Selection Bias

Studies have shown that humans are simply incapable of making unbiased, random choices. For example, when people are asked to choose random numbers more will tend to select odd numbers than even. Whether we like it or not, we are all susceptible to our biases and predispositions and in many significant scenarios these tendencies are entirely unacceptable.

Customs controllers at our borders, for example, need to maintain throughput while ensuring minimal contraband enters the country. So they might endeavour to randomly select passengers, or goods-in-transit, for rigorous checks. It would be impractical to thoroughly search every passenger and every piece of cargo so they rely on randomised selection. But human bias is inevitably involved unless a truly randomised selection system is employed.

What is Unconscious Bias?

Bias can be defined as a prejudice either in favour of something or against it. Bias can be classified as either conscious bias, also known as explicit bias, or unconscious bias, also called implicit bias.

We are all susceptible to unconscious bias. The following quote neatly describes implicit or unconscious bias:

“Our implicit biases are the result of mental associations that have formed by the direct and indirect messaging we receive, often about different groups of people. When we are constantly exposed to certain identity groups being paired with certain characteristics, we can begin to automatically and unconsciously associate the identity with the characteristics, whether or not that association aligns with reality.”


It should be noted that biases, whether conscious or unconscious, are not restricted to ethnicity and race. Biases may exist toward any social group based on a multitude of factors including age, gender identity, physical abilities, religion and many other characteristics. Unconscious biases relate to social stereotypes that we all form outside of our conscious awareness. All of us hold unconscious beliefs about various groups which stem from our human tendency and inclination to categorise our social worlds. Unconscious biases are often at odds with our conscious values but can become manifest under certain conditions and in some situations.

What is Selection Bias?

The term ‘selection bias’ is most commonly used in research situations wherein research subjects are required to be chosen at random. Selection bias can be simply defined as a nonrandom selection.

Humans are simply incapable of making truly random selections which, in research, can have significant consequences. In many other scenarios selection bias can have potentially serious legal implications. For example, if a subject was to claim they had been victimised or selected due to prejudice. In these situations it`s essential that selection bias is entirely avoided.

Objective, Random Selection

There are many everyday, non-research situations in which people are required to make objective, truly random selections. They include:

Random selection of passengers and travellers for thorough searches.

Random selection of baggage for thorough inspection.

Random selection of college and school students for security.

Random selection of staff to prevent pilfering.

Random selection of vehicles for roadworthiness checks and stolen property.

Random selection of event attendees for security and drug screening.

Random selection of goods-in-transit and parcels for inspection.

There are many additional scenarios in which random selection is essential. Our natural human tendencies mean that, without assistance, non of us are capable of making truly random choices. That’s why we need help.

Random Search Selectors

We have previously highlighted the benefits provided by our range of Random Search Selectors.

Avoid Bias with Random Search Selectors

These simple yet highly effective devices have been extremely popular since being launched on our website way back in 2009. They are now widely used and relied upon in a huge range of situations, ensuring human bias doesn’t influence the choices made by people in positions of responsibility.

Our original mains powered Random Search Selector units continue to be extremely popular today. Accessories, including the Remote Activation Button and the Remote Indicator Unit, have increased the system’s versatility and the introduction of the battery powered handheld range has significantly expanded the number of happy users.

Battery powered Random Search Selector units use 3 x AA batteries that reliably provide up to around 50,000 button activations which, in most situations, typically takes over 12 months.

High Throughput with Zero Bias

Our Random Search Selectors effectively remove the unavoidable human tendency to make non-random selections. And importantly, they fulfil a primary objective to reduce the length of time it takes to rigorously check a group of people or assess a range of objects (bags, parcels, vehicles etc.), often in highly pressured, stressful situations.

Random Search Selector units are configured by means of internal DIP switches which set the required selection percentage, totally alleviating the operator of the selection responsibility. For example, a quality controller responsible for randomly selecting and inspecting products from a production line might use a 2% setting to select 1 item in every 50 for detailed quality control evaluation. If the selected 2% of items subjected to inspection are all found to meet requirements then the whole consignment gets a stamp of approval. But if an inspected item fails the inspection then a more extensive batch assessment might be triggered.

Our Random Search Selectors are particularly beneficial in situations where people need to be randomly selected without the possibility of bias influencing the selections made. Those responsible might be checking for weapons, drugs or contraband. There may be a need to randomly select members of staff to check for stolen goods as they leave work or the requirement to randomly select vehicles for inspection as they depart from a commercial site.

Random Search Selectors ensure human bias is completely removed from the selection process, alleviating operators of this onerous responsibility and avoiding potential legal headaches. They make the selection and inspection process more efficient, transparent and reliable and ensure throughput levels are maintained.

Ease of Use

A key attribute of our Random Search Selectors is that they are super-easy to use. Operators don’t need to attend training courses as the units are simple and entirely intuitive.

The percentage of searches required is set internally via secure DIP switches that allow settings from 0.5% to 100%. As each person, package, vehicle or item passes the check point the operator simply presses the big red activation button. The Random Search Selector immediately responds with a ‘Pass’ or ‘Search’ instruction. It couldn’t be simpler.

The beauty of the Random Search Selector is that, although over a period of time the percentage of Search or Pass results, as set via the DIP switches, will be achieved, each individual result is reliably unpredictable and random. So the operator cannot ever be accused of discrimination, favouritism or bias.

Having proven its worth over and again, the battery powered unit has become a firm favourite with users in a wide range of applications from speeding up the processing people at large sporting and music events, to fleet managers using the clipboard “Spot Checker” version to check vehicles entering or leaving a site.

Dual Check Random Search Selectors

Valuable feedback from Random Search Selector users highlighted how it would be really great if they could have a unit that could carry out multiple checks with a single activation, so the “Dual Check” Random Search Selector unit was born.

Dual Check Random Search Selector

The new Dual Check Random Search selector units feature a choice of three labelled advisory lights with a choice of wording:

The Alcohol Drugs check unit shows: Pass / Alcohol / Drugs

The Dual Search Unit shows: Pass / Search 1 / Search 2

The Dual Check Unit Shows: Pass / Check 1 / Check 2

Operational simplicity has been maintained. Internally the new units use 2 sets of DIP switches to configure the required percentages but these clever units have been designed to offer maximum versatility. They can easily be set to operate just one of the indicators or provide both indications simultaneously.

For example, a Dual Check Random Search Selector unit with the ”Pass”, “Check 1” and “Check 2” facility might be used to indicate the need for a Bag Search, a Body Search, or both.

If, after pressing the big red button, the operator is presented with a ‘Pass’ result, the subject is allowed to pass the check point with no further action. If they see a ‘Check 1’ result this would prompt for a bag search. And if they are presented with a ‘Check 2’ indicator this would tell the operator to carry out a body search. If both ‘Check1’ and ‘Check 2’ indicators randomly illuminate simultaneously then both bag and body check actions would be required.

Importantly, the operator isn’t burdened with the need to make these random selections. The Random Search Selector reliably does that for them.

If you would like to learn more about how our Random Search Selectors can help you please give us a call on 01273 475500. We are always happy to help.

For more information on  How to Avoid Selection Bias  talk to  Insight Security

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