Inclusion and Exclusion Criteria in Research

It is a common practice in clinical studies to clearly identify the inclusion and exclusion criteria for the research participants. The researcher uses a criteria that defines what participants should participate in the clinical trial. The researcher also specify a criteria to explain why other participants cannot participate in the research.

Factors influencing inclusion and exclusion criteria

The inclusion of the respondents is dependent on the factors that help meet the goals of the study. Respondent whose demographic, geographic or medical characteristics meet the requirement of the study are included in the study. Exclusion criteria of the study is dependent on any external characteristics of the respondents that can impact the study and make it incorrect or biased.


For example the researcher is studying the prevalence of the major coronary diseases in adult males in the rural areas of the North Carolina.

Inclusion criteria:

The inclusion criteria for the above example would be adult male above 40 years of age, with major heart diseases (what is considered major in this case needs to be defined as well), their geographical location should be rural areas of North Carolina, and currently going through the disease.

Exclusion criteria:

The exclusion criteria include all the participants that meet all the requirements of the study but still the researcher cannot include them in the study. Why? because these respondents have other emotional, medical, or psychological conditions that can influence the results of the study; or these respondents have lake of willingness and interest that can make the study biased and incorrect.

It is very important that the researcher clearly define what are the inclusion criteria and what are the exclusion criteria. These criteria should be mutually exclusive so that the right respondents are selected. By clearly defining the criteria the researcher avoid any confusion as well as bias in the study. The external validity of the research is improved with the right selection and exclusion of the respondents.

Demographic characteristics

The demographic characteristics of the participants may effect the choice of the participant sin the study. Participants’ age, sex, race, ethnicity, marital status, and or number of children can influence the selection criteria. In clinical trials any one or more of the above mentioned characteristics can influence the study. For example in studying the prevalence of diabetes I in teenage boys in Virginia suburbs, the researcher has to use many of the above demographic characteristics as a selection criteria. The researcher will exclude other participants from the study because they cannot fit in the requirement of the study.

The exclusion of a respondent is determined by having other characteristics that can interfere with the main goals of the study. It is important to look deeply and identify those characteristics to improve the external validity of the research.

Geographic characteristics

Obviously geographic characteristics are as important as the demographic characteristics of the respondents. The research problem, objectives and hypothesis define what geographical characteristics define the selection of the participants. The exclusion of a respondent will be determined by other characteristics of the respondent that may influence the study although the respondent has the same geographic characteristics that are present in another respondent who is selected for the study.

Type of disease

The type of disease that needs to be studied is also a major factor to consider when selection is done for the participants. Not only the type of disease but the stage of the disease and the extent is important to consider before selecting the participants. For example, to study the stages of Type I Diabetes in elderly people, the researcher will select exclusive participants for each stage of diabetes I. It is important that the selection is done with clearly defined parameters so that the right participants are selected and there is no chance of overlap or incorrect sample selection.

Subject appropriateness

Overall, subject appropriateness is necessary to ensure right respondents have been selected for the study. This appropriateness means that the goals of the study can be reached with the participants selected. The respondents should provide justification for the study. The major criteria for the study should be the primary condition or intervention that needs to be studied.

Possible reasons for exclusion

There can be many reasons that influence the exclusion criteria of the participants.

  1. The intervention can be harmful for the respondent.
  2. The respondent does not provide consent for the participation in the study.
  3. The participants may lose interest and will not adhere to the study.
  4. The participant is not reliable.
  5. The participant has any other medical condition that can interfere with the study and can make it incorrect or biased.
  6. The participant is unwilling to provide personal information to the researcher.
  7. Any chronic disease other than the one that is being studied that will impact respondents’ availability for the study.




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