Very simply, generalizability is a measure of how useful the results of a study are for a broader group of people or situations. Show
If the results of a study are broadly applicable to many different types of people or situations, the study is said to have good generalizability. If the results can only be applied to a very narrow population or in a very specific situation, the results have poor generalizability. This concept is especially important for individuals living with hydrocephalus because there are so many different causes of hydrocephalus, comorbidities, and secondary complications. In many studies, the study participants represent a very specific group of hydrocephalus patients. Examples are studies that include only X-linked hydrocephalus patients or patients with post-hemorrhagic hydrocephalus. These populations are unique in many ways and therefore, depending on the specifics of the study, the results may not apply to other patient groups. Likewise, a study looking at long-term cognitive outcomes in shunted patients may not be applicable to patients with an endoscopic third ventriculostomy (ETV). What limits the generalizability of a research project and how can you tell if the results of a study apply to you? Let’s work through a study to find out. What are we studying?We want to know if brisk walking lower blood sugar levels. What is the study design?It is easy to get male and female college students to participate in research studies. So, the researchers randomly assign students at the local college to Group A or Group B and take a baseline blood sugar measurement. Group A will briskly walk for 30 minutes every day for five weeks. Group B will be asked to continue their normal activities. At the end of the experiment, researchers will measure blood sugar levels again. This is a well-designed prospective, randomized control trial.  The ResultsAt the end of the five weeks, researchers conclude that brisk walking significantly lowers blood sugar levels. How Generalizable are these Results?The generalizability of this study is limited by the characteristics of the study participants. Remember our study population was made up of male and female college students. Most college students are between the ages of 18-22 years old, so it may be reasonable to generalize the results to other young adults assuming a large sample size and diversity among participants. Things get trickier, however, if one would like to generalize the results to senior citizens. There are a lot of factors that make college students different from seniors including differences in baseline activity, blood pressure, baseline blood sugar levels, and what each may consider a ‘brisk’ walking pace. These differences may limit the generalizability of the study to older populations, or, in other words, the results may not apply to older adults. The specific intervention being tested can also limit how generalizable a study is. In this example, study participants were asked to walk ‘briskly.’ Would the results have been different if the participants had been asked to run, or swim, or lift weights? The Take AwayWhen you read a research paper, pay close attention to:
Then decide if the characteristics of the group are similar to your specific experience. If your case is reflected in the study group characteristics, the study results are likely applicable to you. But remember, every case is unique and group averages may not mirror your experience. Generalizability is the degree to which you can apply the results of your study to a broader context. Research results are considered generalizable when the findings can be applied to most contexts, most people, most of the time. Example: GeneralizabilitySuppose you want to investigate the shopping habits of people in your city. You stand at the entrance to a high-end shopping street and randomly ask passersby whether they want to answer a few questions for your survey.Do the people who agree to help you with your survey accurately represent all the people in your city? Probably not. This means that your study can’t be considered generalizable. Generalizability is determined by how representative your sample is of the target population. This is known as external validity. Table of contentsWhat is generalizability?The goal of research is to produce knowledge that can be applied as widely as possible. However, since it usually isn’t possible to analyze every member of a population, researchers make do by analyzing a portion of it, making statements about that portion. To be able to apply these statements to larger groups, researchers must ensure that the sample accurately resembles the broader population. In other words, the sample and the population must share the characteristics relevant to the research being conducted. When this happens, the sample is considered representative, and by extension, the study’s results are considered generalizable. In general, a study has good generalizability when the results apply to many different types of people or different situations. In contrast, if the results can only be applied to a subgroup of the population or in a very specific situation, the study has poor generalizability. Why is generalizability important?Obtaining a representative sample is crucial for probability sampling. In contrast, studies using non-probability sampling designs are more concerned with investigating a few cases in depth, rather than generalizing their findings. As such, generalizability is the main difference between probability and non-probability samples. There are three factors that determine the generalizability of your study in a probability sampling design:
Increasing sample diversity can help researchers develop theories of human nature that reliably explain human behavior across countries and cultures instead of among only a thin slice of humanity. Generalizability is one of the three criteria (along with validity and reliability) that researchers use to assess the quality of both quantitative and qualitative research. However, depending on the type of research, generalizability is interpreted and evaluated differently.
Examples of generalizabilityGeneralizability is crucial for establishing the validity and reliability of your study. In most cases, a lack of generalizability significantly narrows down the scope of your research—i.e., to whom the results can be applied. Example: Narrowed scopeYou are researching the voting intentions of a small town of 3,000 residents. Due to limited time and resources, you plan to take a sample of 100 people.Luckily, you have access to an anonymized list of all residents. This allows you to establish a sampling frame and proceed with simple random sampling. With the help of an online random number generator, you draw a simple random sample. After obtaining your results (and prior to drawing any conclusions) you need to consider the generalizability of your results. Using an online sample calculator, you see that the ideal sample size is 341. With a sample of 341, you could be confident that your results are generalizable, but a sample of 100 is too small to be generalizable. This limitation of your research should be mentioned in your discussion section. However, research results that cannot be generalized can still have value. It all depends on your research objectives. Example: Non-generalizable researchSuppose you are conducting a study among visitors of the Getty Museum. You are particularly interested in how families with young children engage with a new interactive exhibit. Your goal is to advise the Getty Museum on future exhibitions geared towards families.You go to the museum for three consecutive Sundays to make observations. Your observations yield valuable insights for the Getty Museum, and perhaps even for other museums with similar educational offerings. However, you can’t claim that your findings represent all the families that visit museums in the country, or even in your city. As you collected a convenience sample, your study results are not generalizable. Nevertheless, in this case, that was not the goal of your research. Your results can still be considered valid for the context in which they were studied. Types of generalizabilityThere are two broad types of generalizability:
Statistical generalizability is critical for quantitative research. The goal of quantitative research is to develop general knowledge that applies to all the units of a population while studying only a subset of these units (sample). Statistical generalization is achieved when you study a sample that accurately mirrors characteristics of the population. The sample needs to be sufficiently large and unbiased. In qualitative research, statistical generalizability is not relevant. This is because qualitative research is primarily concerned with obtaining insights on some aspect of human experience, rather than data with solid statistical basis. By studying individual cases, researchers will try to get results that they can extend to similar cases. This is known as theoretical generalizability or transferability. How do you ensure generalizability in research?In order to apply your findings on a larger scale, you should take the following steps to ensure your research has sufficient generalizability.
After completing your research, take a moment to reflect on the generalizability of your findings. What didn’t go as planned and could impact your generalizability? For example, selection biases such as nonresponse bias can affect your results. Explain how generalizable your results are, as well as possible limitations, in the discussion section of your research paper. Frequently asked questions about generalizabilityWhy is generalizability important in research? Generalizability is important because it allows researchers to make inferences for a large group of people, i.e., the target population, by only studying a part of it (the sample). What is the difference between internal and external validity? Internal validity is the degree of confidence that the causal relationship you are testing is not influenced by other factors or variables. External validity is the extent to which your results can be generalized to other contexts. The validity of your experiment depends on your experimental design. What goes in the discussion chapter of a dissertation? In the discussion, you explore the meaning and relevance of your research results, explaining how they fit with existing research and theory. Discuss:
How do I determine scope of research? Scope of research is determined at the beginning of your research process, prior to the data collection stage. Sometimes called “scope of study,” your scope delineates what will and will not be covered in your project. It helps you focus your work and your time, ensuring that you’ll be able to achieve your goals and outcomes. Defining a scope can be very useful in any research project, from a research proposal to a thesis or dissertation. A scope is needed for all types of research: quantitative, qualitative, and mixed methods. To define your scope of research, consider the following:
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