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Published by at April 28th, 2023 , Revised On December 8, 2023

Research Bias – Definition, Types & Examples

“Bias in research refers to systematic errors in a study’s design, conduct, or analysis that can affect the results’ accuracy, validity, and reliability. It occurs when researchers introduce their personal opinions, beliefs, or preferences or fail to account for all relevant variables that could influence the outcomes.”

Bias can arise in different forms, such as selection bias, measurement bias, publication bias, and confirmation bias. Bias in research can compromise the validity and generalisability of the findings and lead to incorrect conclusions, unjustified claims, or flawed recommendations.

To tackle the issue of bias, researchers should employ rigorous data collection, analysis, and interpretation methods, adhere to ethical standards and principles, disclose potential conflicts of interest, and consider multiple perspectives and sources of evidence.

Definition of Research Bias

In research, bias refers to any systematic error or deviation from the truth during a study’s design, conduct, or analysis. Bias in research can arise when researchers have personal beliefs, preferences, or expectations that influence their study design or interpretation of results or when there are flaws in the methodology or data collection that compromise the validity and reliability of the findings.

Quick Example of Bias in Research 

An example of bias in research is bias in a clinical trial. Let’s say that a new drug is being tested to treat a particular condition, and the researchers only recruit participants from a single hospital or medical centre. Suppose the patients in that hospital have different characteristics or demographics than the broader population of people with the condition. In that case, the study results may not be generalisable to the wider population.

Types of Bias in Research

Several types of research bias can occur during a study’s design, conduct, analysis, or reporting. Here are some common types of research bias:

Information bias: is seen when there are errors or limitations in measuring exposure or outcome variables in a study. This can lead to incorrect estimates of the association between variables and arise due to measurement error, misclassification, or incomplete or inaccurate data.

Interviewer bias: refers to the systematic error that can arise when an interviewer’s personal beliefs, expectations, or behaviour influence the responses given by the interviewee.

Selection bias: occurs when the sample or participants are not representative of the target population or when certain groups are systematically excluded or overrepresented.

Measurement bias: This type of research bias takes place when the measurement instruments or methods used to collect data are not valid or reliable or when the assessors are not blinded to the study group or intervention.

Reporting bias: generally occurs when the study results are selectively reported or misrepresented or when the data analysis is biased toward a particular outcome or conclusion.

Publication bias: occurs when studies with positive or significant results are more likely to be published than those with negative or non-significant results, leading to a distorted view of the evidence.

Confounding bias: occurs when a third variable influences the relationship between the exposure and the outcome, leading to a spurious association or false conclusion.

Recall bias: occurs when the participant’s ability to recall or report their past experiences or behaviours is compromised, leading to inaccurate data.

Observer bias: observer bias is reported when the observers or data collectors are aware of the study group or intervention, leading to biased measurement or interpretation of the data.

Regression to the mean: this is a statistical phenomenon that occurs when a variable measured at an extreme value on one occasion is likely to be measured closer to the mean on a subsequent occasion. This phenomenon occurs due to the presence of random fluctuations in the measurement of the variable.

Sampling bias: occurs when the sampling method or technique used to select the participants is not random or representative of the target population, leading to biased estimates or conclusions.

Performance bias: a type of bias in research that can occur when there are differences in how participants are treated or managed during a study, which can affect the outcomes being measured. This bias can arise due to issues such as lack of blinding or unequal provision of care or treatment.

Response bias: Response bias occurs when participants provide incorrect or misleading responses to survey or interview questions. This can be due to social desirability bias, acquiescence bias, or interviewer bias, resulting in biased data and incorrect conclusions.

Cognitive bias: refers to systematic errors in thinking or judgment that can lead to deviations from rational or objective decision-making. These biases can arise due to mental shortcuts or heuristics, such as overconfidence, confirmation bias, or the availability heuristic, and can affect our perceptions, beliefs, and behaviours.

Researcher bias: Researcher bias refers to the systematic errors or distortions that can arise due to the personal beliefs, preferences, or expectations of the researcher conducting a study. This can result in biased selection of participants, measurement of variables, or interpretation of results. Researcher bias can occur consciously or unconsciously, affecting the validity and reliability of research findings. Measures to control researcher bias can include blinding, randomisation, and standardisation of procedures.

Researchers need to be aware of these types of biases and take steps to control them during the research process to ensure the validity and reliability of the study findings.

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Examples of Research Bias

Example: Selection Bias

Selection bias in research is a study that examines the effects of a new medication on a particular disease but only includes patients willing and able to participate in the study. This may result in a biased sample not representative of the broader population of patients with the disease, and the study findings may not be generalisable to the larger population.

For instance, let’s say that the study only includes patients with mild or moderate symptoms of the disease but excludes those with severe symptoms or co-morbid conditions that would make them ineligible or unwilling to participate. This could lead to overestimating the medication’s effectiveness, as the study only includes patients more likely to respond positively to the treatment.

Alternatively, let’s say that the study only includes patients from a single geographic area or medical centre and does not include patients from other regions or medical centres. This could lead to a biased sample not representative of the diversity of patients with the disease, and the study findings may not be generalisable to other populations.

To control selection bias, researchers should use appropriate sampling methods that ensure a representative sample of the population and should strive to recruit a diverse range of participants who reflect the diversity of the population under study.

Example: Measurement Bias

Measurement bias in research is a study that measures the effectiveness of a new treatment for depression using self-reported measures of mood and symptoms but does not use any objective measures or clinical assessments.

For example, if the study relies solely on self-reported questionnaires completed by the participants, there may be a risk of bias due to social desirability or recall bias. Participants may be inclined to provide responses they think the researchers want to hear or may have difficulty recalling their symptoms accurately.

Alternatively, suppose the study uses observer-rated measures of mood and symptoms. In that case, there may be a risk of bias if the observers are not blinded to the treatment group or if their ratings are influenced by their expectations or preconceptions.

To tackle measurement bias, researchers should use validated and reliable measures of the outcome variables and ensure that the assessors are blinded to the treatment group or intervention. They should also consider using multiple measures or assessments to triangulate the results and increase the validity and reliability of the study findings.

Example: Reporting Bias

An example of reporting bias in research is a study that finds no significant difference between two treatments for a particular condition. Still, the authors only report the positive findings and do not mention the non-significant results.

For example, a study compares two different surgical techniques for a particular condition and finds no significant difference in outcomes between the two groups. However, the authors only report the positive findings, such as the fact that both techniques effectively reduced pain and improved function, and do not mention that there was no statistically significant difference between the two groups.

This reporting bias can lead to a distorted view of the study findings. It can create the impression that one treatment is superior to the other, even though the evidence does not support this conclusion.

To deal with reporting bias, researchers should report all of the study results, including both positive and negative findings. They should avoid selectively reporting only the findings that support their preconceptions or hypotheses. They should also follow established reporting guidelines, such as the Consolidated Standards of Reporting Trials (CONSORT) statement, to ensure that their study is reported transparently and completely.

Example: Publication Bias

Publication bias in research is when studies that report positive or statistically significant results are more likely to be published than those that report negative or non-significant results.

Let’s consider that a pharmaceutical company conducts multiple clinical trials of a new drug for a particular condition. Suppose some trials find positive results and some negative or non-significant results. In that case, the company may only choose to publish the positive results, not the negative or non-significant ones.

This publication bias can lead to a distorted view of the overall evidence, as it creates a situation where the published studies only represent a subset of the total studies that have been conducted. This can lead to an overestimation of the drug’s effectiveness and can lead to inappropriate or unsafe clinical decisions.

You can control publication bias by striving to publish all of their study results, regardless of whether they are positive, negative, or non-significant. Journals and publishers can also reduce publication bias by adopting policies and practices that encourage the publication of all types of studies and discourage selective reporting or publication.

Example: Confounding Bias

An example would be a study examining the relationship between coffee consumption and the risk of heart disease while ignoring other factors influencing the results, such as age, smoking status, or physical activity level.

Let’s say the study finds that people who drink more coffee have a higher risk of heart disease; this could be due to a confounding variable such as age, as older people may be more likely to drink more coffee and also more likely to have heart disease. The study findings could be biased and misleading if the researchers did not control for age in their analysis.

Researchers should identify potential confounding variables in advance and control for them in their study design and analysis. This can be done through stratification, regression analysis, or matching techniques. Researchers should also use appropriate statistical methods to assess the potential impact of confounding variables on the study results and report any limitations or caveats related to the study findings.

Example: Recall Bias

One example of recall bias in research is a study that asks participants to recall their past behaviours or experiences, such as their diet or physical activity level, but the participants may not accurately remember or report their behaviours due to memory bias.

Let’s consider an example of a study that asks participants to recall their dietary habits over the past year, including how often they ate certain foods. If some participants have difficulty remembering their past behaviours or overestimating or underestimating their consumption, this could introduce recall bias into the study results.

This recall bias can lead to an inaccurate or incomplete picture of the true relationship between diet and health outcomes and can compromise the validity of the study findings.

To minimise recall bias, researchers can use different strategies such as conducting a validation study to assess the accuracy of participants’ recall, using objective measures or biomarkers to corroborate the self-reported data, and reducing the recall period to a shorter time frame that participants are more likely to remember accurately.

Example: Observer Bias

An example of observer bias in research is a study that uses a subjective measure, such as a rating scale or a questionnaire. The observer’s expectations or preconceptions influence their interpretation of the data.

For example, let’s say that a study examines the effectiveness of a new therapy for children with autism. The study involves an observer who rates the children’s behaviour using a rating scale before and after the therapy. However, the observer may have preconceptions about the therapy, and their expectations could influence their interpretation of the children’s behaviour, leading to observer bias.

This observer bias can lead to an overestimation or underestimation of the true effect of the therapy and can compromise the validity of the study findings.

To overcome observer bias, researchers can use different strategies such as blinding the observer to the treatment group (i.e., not revealing which children received the therapy), using objective measures whenever possible, and using multiple observers to ensure inter-rater reliability.

Example: Sampling Bias

An example of a sampling bias would be a study evaluating the prevalence of a certain disease in a particular region, but the study only recruits participants from hospitals or clinics and does not include people who may have the disease but have not sought medical care. This sampling bias can lead to an overestimation or underestimation of the true prevalence of the disease in the population, and the study findings may not be generalisable to the broader population.

Another example of sampling bias could be a political survey conducted only on social media, which excludes people who are not active on social media, leading to a biased sample.

Researchers should use appropriate sampling methods to ensure that the sample is representative of the target population and that all eligible individuals have an equal chance of being included in the study in order to minimise sampling bias. This can be done through random, stratified, or other probability-based sampling methods. Researchers should also report any limitations or potential biases related to the study sample in their study findings.

Example: Performance Bias

Let’s talk about performance bias in a study that compares the effectiveness of two treatments, where the participants or researchers are not blinded to the treatment assignment, leading to biased or ungeneralisable results.

For example, let’s say that a study compares the effectiveness of a new medication versus a placebo for treating depression. However, the participants or researchers may know which treatment the participant receives, which can lead to performance bias. The participants who receive the new medication may expect to feel better and therefore report feeling better, regardless of the actual effectiveness of the medication.

This performance bias can lead to an overestimation of the true effect of the treatment and can compromise the validity of the study findings.

Researchers can control performance bias by using different strategies ,such as blinding the participants and researchers to the treatment assignment, using placebo treatments, or using objective measures to assess the outcomes. Blinding can be single-blind (where the participants are unaware of their treatment assignment) or double-blind (where the participants and researchers are unaware of the treatment assignment).

Example: Researcher Bias

An example of researcher bias in research is when the researcher’s expectations, beliefs, or opinions influence the study design, data collection, analysis, or interpretation of the study findings, leading to biased or ungeneralisable results.

A researcher may strongly believe that a certain treatment is effective, leading them to overemphasise the positive results and downplay the study’s negative results. Alternatively, a researcher may have a personal or financial interest in particular findings of the study, which may influence their interpretation of the data.

Researchers can control the bias by employing strategies such as blinding themselves to the treatment assignment, using objective measures, using standardised protocols, and involving multiple researchers to ensure inter-rater reliability. Additionally, researchers can disclose any potential conflicts of interest or biases in their study findings to ensure transparency and accountability.

Example: Response Bias

For example, if participants in a study about drug use are afraid of being judged or punished for their behaviour, they may under-report or deny drug use altogether. Alternatively, participants may over-report or exaggerate their drug use to appear more socially desirable. This response bias can lead to inaccurate estimates of drug use prevalence or patterns in the study population.

Another example of response bias could be a study on voting behaviour where participants may want to keep their true political affiliation private or may overstate their voting intention to please the researcher.

Researchers can control response bias by applying techniques such as anonymous surveys, using validated questionnaires, framing questions objectively and non-judgmental way, and emphasising the importance of honest and accurate responses. Additionally, researchers can collect data on non-response and attempt to adjust for it in their analysis to ensure that their results represent the target population.

Example: Information Bias

In a study on alcohol consumption and heart disease, information bias could occur if participants do not accurately report their alcohol intake or if the study relies on self-reported alcohol consumption rather than objective measures such as biomarkers. This could lead to inaccurate estimates of the relationship between alcohol consumption and heart disease.

Another example could be a study on the effectiveness of a medical intervention that relies on medical records to determine outcomes. If the medical records are incomplete or inaccurate, the study results could be biased or misleading.

You can deal with information bias by using validated measures, minimising missing data, training data collectors, conducting pilot studies to refine measurement protocols, and using objective measures when possible. Researchers can also conduct sensitivity analyses to assess the impact of measurement error on their study results.

Example: Cognitive Bias

Cognitive bias refers to systematic errors or deviations from rational thinking and judgment due to research limitations in human cognition. A specific example of cognitive bias is confirmation bias, which is the tendency to search for, interpret, or remember information to confirm pre-existing beliefs or hypotheses while ignoring or rejecting information that contradicts them.

For example, if a researcher believes that a certain treatment is effective, they may unconsciously seek evidence that supports their belief while dismissing or ignoring evidence that contradicts it. This can lead to biased interpretations of the data and confirmation of pre-existing beliefs rather than objectively evaluating the evidence.

Similarly, confirmation bias can occur in everyday life when individuals seek information supporting their beliefs or opinions while rejecting information that challenges them. For instance, in a political debate, a person may selectively interpret or remember evidence supporting their political views while ignoring or dismissing evidence contradicting them.

Individuals can seek out diverse sources of information, actively consider alternative perspectives, and engage in critical thinking and self-reflection to overcome the problem of cognitive bias. In research, researchers can use strategies such as blinding themselves to the treatment assignment and using objective measures to assess outcomes to the impact of confirmation bias.

Example: Regression to the Mean (RTM)

Let’s consider a study that measures the academic performance of a group of students. The students are selected based on their low scores in a preliminary exam. In the subsequent exam, even if the students do not receive any intervention, some will improve their scores, and some will perform worse. However, the students who performed extremely poorly on the preliminary exam are likelier to have had measurement errors or other random factors that lowered their scores. On the subsequent exam, these same factors may not be present, and thus their scores are likely to improve, moving closer to the mean.

This phenomenon can also occur in natural weather patterns or biological processes. For example, a plant that has experienced extreme growth in a particular season may experience a decline in the subsequent season due to the influence of random fluctuations in environmental factors.

Regression to the mean can be a confounding factor in research studies, especially those that use extreme values as selection criteria. To minimise the impact of regression on the mean, researchers can use a control group, random assignment, or repeated measurements of the same variable to identify the true effects of the intervention or variable of interest.

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Tips to Avoid Bias in Research

Avoiding bias in research is important for ensuring the accuracy and reliability of study results. Here are some strategies that can help prevent bias in research:

  • Develop a study protocol: Before starting the study, develop a detailed study protocol that outlines the research question, study design, data collection methods, and data analysis plan. This will help ensure that the study is conducted in a standardised and objective manner.
  • Use a representative sample: Ensure that the study sample represents the population being studied to avoid selection bias. Random sampling or stratified sampling can help achieve a representative sample.
  • Use blinding: Use blinding methods such as double or single-blinding for the observer and performance bias. Blinding involves concealing the identity of the treatment group or study participants from the researchers or study participants.
  • Use objective measures: Use objective measures to assess outcomes and measurement bias. For example, using laboratory tests or clinical assessments rather than relying on self-reported measures.
  •  Confounding variables: Account for potential confounding variables in the study design and data analysis to confounding bias. This can be achieved through stratification, matching, or statistical adjustment.
  • Use validated measures: Use validated measures or instruments to ensure that the collected data is reliable and accurate.
  • Monitor data collection: Regularly monitor data collection to ensure that the study protocol is followed correctly and that there are no deviations or errors.
  • Be aware of cognitive biases: Be aware of common cognitive biases such as confirmation, recall, and response biases and take steps to minimise their impact on the study results.
  • Use peer review: Have the study reviewed by other researchers or experts to ensure that the study design, methods, and analysis are sound and unbiased.

By following these strategies, researchers can help reduce bias and ensure their study results are accurate and reliable.

By following these strategies, researchers can help reduce bias and ensure their study results are accurate and reliable.

Frequently Asked Questions

Bias in research can be a problem because it can lead to inaccurate or unreliable study results. When bias is present in a study, it can distort the findings, leading to incorrect conclusions or recommendations.

This can have significant consequences, particularly regarding decision-making in healthcare, public policy, and scientific research. Bias can arise at various stages of the research process, such as during the study design, data collection, analysis, or interpretation. Some common types of bias in research include selection bias, measurement bias, reporting bias, publication bias, and confounding bias.

Bias can also result from various factors, such as the researcher’s personal biases, unconscious biases, financial interests, pressure to produce positive results or lack of awareness of potential sources of bias. The presence of bias in research can undermine the credibility and validity of study results, reducing the confidence that can be placed in the findings. This can significantly affect public health, policy decisions, and clinical practice. For example, a biased study that recommends an ineffective or harmful treatment could put patients at risk, waste resources, and have long-term consequences.

Therefore, researchers need to be aware of the potential sources of bias, take steps to minimise them, and report on any limitations or potential biases in their study results. This can help ensure that the research findings are reliable and accurate and can inform decision-making in a meaningful and impactful way.

Response bias is when participants answer inaccurately or dishonestly. No-response bias is when participants skip questions, leading to missing data.

About Owen Ingram

Avatar for Owen IngramIngram is a dissertation specialist. He has a master's degree in data sciences. His research work aims to compare the various types of research methods used among academicians and researchers.