The effects of selection bias have been considered for a long time, and not just in research. Also in business and everyday life we selectively select information and expose ourselves to distorted data . Cognitive biases contribute greatly to making mistakes in selection processes and, consequently, to obtaining erroneous results.
People are victims of selection bias all the time, which shows that we are not impartial , but that we must try very hard to at least aspire to a state of neutrality. The following examples reveal the profound implications of this bias.
Suppose we want to conduct a general brand awareness survey of a healthy dietary supplement. If we carry out the survey in gyms, health food stores or organic supermarkets, we will only ask the target audiences of said product. This can be useful, but the results should be evaluated with caution, because they will already be conditioned by the selection bias: in general, customers of gyms, health food stores or organic supermarkets are more receptive to the effectiveness and usefulness of healthy products. Therefore, it can be assumed that these groups will know the brand better than the rest of the people and that, consequently, the data will not have been evaluated in a neutral way.
Our second example of selection bias reveals the serious consequences of not choosing the sample subjects truly randomly. Let's suppose that a research team wants to carry out a survey on the economic situation of a country that represents as much as possible all the companies. However, to select the data, it uses the commercial register, so it only chooses the corporations and commercial companies that appear in that list. In this case, the selection bias is much greater than it may appear at first glance: due to its effect, the study not only excludes small businesses, but also the many freelancers, such as lawyers, doctors, architects or artists. , and to professionals who work part-time in all sectors.
This mistake is very obvious, and more experienced researchers probably won't make it. However, selection bias can appear in studies in a much more subtle way, distorting something as important as a country's economic forecast.