Undercoverage biasis the predisposition that occurs when some members the a populace are inadequately represented in the sample.

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This form of bias often wake up in convenience sampling and voluntary response sampling, in which you collect a sample that is basic to obtain but is often prone to undercoverage of details members of a population.

Why is Undercoverage predisposition a Problem?

Undercoverage bias is a problem because itcauses the sample to be unrepresentative the the population.The point of collecting data because that a sample is to achieve data in a method that is quicker and easier than collecting data for whole population, and to have the ability to extrapolate the findings from the sample to the larger population.

In order come extrapolate the findings, though, the sample requirements to be representative the our populace as a whole. Ideally us would favor our sample to be a “mini” version of the population. Unfortunately, undercoverage bias can cause the world in ours sample come be substantially different 보다 the people in the larger population.

For example, expect researchers desire to know what citizens in a certain city think the a potential new law. To collection data, they go to a nearby library and ask civilization that walk in what they think that the potential new law. Back this is a convenient method to conference data, the researchers hazard undercoverage of several species of people, including:

People who are houseboundPeople who just don’t prefer visiting the libraryPeople that go to a different library in a different component of the city

Because this research excludes certain types of people, the outcomes of the study room unlikely to it is in representative of the population.

For example, suppose the world who go to this particular library space far much more likely to be donate of the potential brand-new law compared to the rest of the population. This method that when the results of the survey space in, that will appear that a big percentage of citizens in this city assistance the potential new law, as soon as in fact most that the citizens execute not.

The visual listed below illustrates this problem: expect the environment-friendly circles represent people who room in favor of the brand-new law if the red one represent human being who room opposed to the new law:

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Notice exactly how most the the civilization who room in favor of the brand-new law are included in the sample, however the sample is not representative of the bigger population. The outcomes of the inspection would display that most civilization are in favor of the brand-new law, once in truth this is not true.

Examples the Undercoverage Bias

The following examples illustrate several instances in i m sorry undercoverage prejudice can occur.

Example 1

Researchers desire to find out what citizens in a specific city think of having a new park built. In order to collect data, researchers attend a local town meeting and ask civilization there about their thoughts. Unfortunately, this kind of convenience sampling is most likely to endure from undercoverage the the adhering to groups:

People who have actually no accessibility to transport to walk to the city meetingsPeople that aren’t even mindful of that reality that town meetings take placePeople who occupational in the evenings and also are simply unable to attend city meetings

Thus, the opinions that these world will not be consisted of in the results of the study. Thus undercoverage that these certain groups, the sample is unlikely to it is in representative the the bigger population.

Example 2

Researchers desire to understand how many hours every day world watch TV in a details county. To collect data for the study, lock randomly choose names from a local phonebook and call human being to asking them about their TV consumption. This is a kind of convenience sampling and also it is most likely to suffer from undercoverage the the complying with groups:

Very wealthy human being who perform not perform their phone number in local phonebooksYoung world who just use cellphones and also do not have their numbers detailed in local phonebooks

Thus, the amount of TV that really wealthy people and also young human being watch will certainly be undercovered in this study. Therefore undercoverage that these particular groups, the sample is i can not qualify to it is in representative of the larger population.

Example 3

Researchers want to recognize what citizens in a particular city think of a brand-new traffic legislation so they offer out a questionnaire to civilization that to walk by at a neighborhood mall. This is a kind of convenience sampling and also it’s most likely to suffer from undercoverage of the complying with groups:

People who have actually no accessibility to transport to walk to the shopping center (and therefore are largely unaffected by website traffic laws)People that don’t choose going come the shopping center (and for this reason may select not to drive in liven areas)People that go come a different mall in a various city

Thus, the opinions of these human being will not be contained in the results of the study. As such undercoverage the these specific groups, the sample is i can not qualify to be representative that the larger population.

How to protect against Undercoverage Bias

Undercoverage predisposition often occurs together a an outcome of convenience sampling. To remove (or at least minimize) the effects of undercoverage bias, a much better form that sampling is making use of a basic random sample.

In this form of sample, every member that a populace has one equal possibility of gift selected to it is in in the sample.

The advantage of this approach is that simple random samples are usually representative the the populace we’re interested in because every member has actually an equal opportunity of being had in the sample.

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When we usage this strategy instead that convenience sampling, we deserve to be an ext confident in our capability to extrapolate the result from the sample to the larger population since it’s likely that members native every (or almost every) group in the populace are consisted of in the sample.

Additional Resources

What is Self-Selection Bias?What is Referral Bias?What is Nonresponse Bias?