Diving Deeper into Limitations and Delimitations

If you are working on a thesis, dissertation, or other formal research project, chances are your advisor or committee will ask you to address the delimitations of your study. When faced with this request, many students respond with a puzzled look and then go on to address what are actually the study’s limitations.

If you’re wondering what the difference between these two terms is, don’t worry—you’re not alone!

In a previous article , we covered what goes into the limitations, delimitations, and assumptions sections of your thesis or dissertation. Here, we will dive a bit deeper into the differences between limitations and delimitations and provide some helpful tips for addressing them in your research project—whether you are working on a quantitative or qualitative study.

Acknowledging Weaknesses vs. Defining Boundaries

These concepts are easy to get confused because both limitations and delimitations restrict (or limit) the questions you’ll be able to answer with your study, most notably in terms of generalizability.

However, the biggest difference between limitations and delimitations is the degree of control you have over them—that is, how much they are based in conscious, intentional choices you made in designing your study.

Limitations occur in all types of research and are, for the most part, outside the researcher’s control (given practical constraints, such as time, funding, and access to populations of interest). They are threats to the study’s internal or external validity.

Limitations may include things such as participant drop-out, a sample that isn’t entirely representative of the desired population, violations to the assumptions of parametric analysis (e.g., normality, homogeneity of variance), the limits of self-report, or the absence of reliability and validity data for some of your survey measures.

Some limitations are inherent to your research design itself. For example, you won’t be able to infer causality from a correlational study or generalize to an entire population from a case study. Likewise, while an experimental study allows you to draw causal conclusions, it may require a level of experimental control that looks very different from the real world (thus lowering external validity). Of course, your choice of research design is within your control; however, the limitations of the design refer to those aspects that may restrict your ability to answer the questions you might like to answer.

Limitations can get in the way of your being able to answer certain questions or draw certain types of inferences from your findings. Therefore, it’s important to acknowledge them upfront and make note of how they restrict the conclusions you’ll be able to draw from your study. Frequently, limitations can get in the way of our ability to generalize our findings to the larger populations or to draw causal conclusions, so be sure to consider these issues when you’re thinking about the potential limitations of your study.

Delimitations are also factors that can restrict the questions you can answer or the inferences you can draw from your findings. However, they are based on intentional choices you make a priori (i.e., as you’re designing the study) about where you’re going to draw the boundaries of your project. In other words, they define the project’s scope.

Like limitations, delimitations are a part of every research project, and this is not a bad thing. In fact, it’s very important! You can’t study everything at once. If you try to do so, your project is bound to get huge and unwieldy, and it will become a lot more difficult to interpret your results or come to meaningful conclusions with so many moving parts. You have to draw the line somewhere, and the delimitations are where you choose to draw these lines.

One of the clearest examples of a delimitation that applies to almost every research project is participant exclusion criteria. In conducting either a quantitative or a qualitative study, you will have to define your population of interest. Defining this population of interest means that you will need to articulate the boundaries of that population (i.e., who is not included). Those boundaries are delimitations.

For example, if you’re interested in understanding the experiences of elementary school teachers who have been implementing a new curriculum into their classrooms, you probably won’t be interviewing or sending a survey to any of the following people: non-teachers, high-school teachers, college professors, principals, parents of elementary school children, or the children themselves. Furthermore, you probably won’t be talking to elementary school teachers who have not yet had the experience of implementing the curriculum in question. You would probably only choose to gather data from elementary school teachers who have had this experience because that is who you’re interested in for the purposes of your study. Perhaps you’ll narrow your focus even more to elementary school teachers in a particular school district who have been teaching for a particular length of time. The possibilities can go on. These are choices you will need to make, both for practical reasons (i.e., the population you have access to) and for the questions you are trying to answer.

Of course, for this particular example, this does not mean that it wouldn’t be interesting to also know what principals think about the new curriculum. Or parents. Or elementary school children. It just means that, for the purposes of your project and your research questions, you’re interested in the experience of the teachers, so you’re excluding anyone who does not meet those criteria. Having delimitations to your population of interest also means that you won’t be able to answer any questions about the experiences of those other populations; this is ok because those populations are outside of the scope of your project. As interesting as their experiences might be, you can save these questions for another study. That is the part of the beauty of research: there will always be more studies to do, more questions to ask. You don’t have to (and can’t) do it all in one project.

Similarly, the focus of the research problem itself (and the associated research questions) is another common source of delimitations. By choosing to focus your research on a particular problem or question, you are necessarily choosing not to examine other problems or questions. Remember: You can’t answer all possible questions with one project. While this may seem obvious, it’s worth acknowledging. There may be other related problems or questions that are equally worthy of study, but you must choose which one(s) you are and which ones you are not looking into with your project.

Continuing with the previous example, for instance, let’s suppose that the problem you are most interested in addressing is the fact that we know relatively little about elementary school teachers’ experiences of implementing a new curriculum. Perhaps you believe that knowing more about teachers’ experiences could inform their training or help administrators know more about how to support their teachers. If the identified problem is our lack of knowledge about teachers’ experiences, and your research questions focus on better understanding these experiences, that means that you are choosing not to focus on other problems or questions, even those that may seem closely related. For instance, you are not asking how effective the new curriculum is in improving student test scores or graduation rates. You might think that would be a very interesting question, but it will have to wait for another study. In narrowing the focus of your research questions, you limit your ability to answer other questions, and again, that’s ok. These other questions may be interesting and important, but, again, they are beyond the scope of your project.

Common Examples of Limitations

While each study will have its own unique set of limitations, some limitations are more common in quantitative research, and others are more common in qualitative research.

In quantitative research, common limitations include the following:

- Participant dropout

- Small sample size, low power

- Non-representative sample

- Violations of statistical assumptions

- Non-experimental design, lack of manipulation of variables, lack of controls

- Potential confounding variables

- Measures with low (or unknown) reliability or validity

- Limits of an instrument to measure the construct of interest

- Data collection methods (e.g., self-report)

- Anything else that might limit the study’s internal or external validity

In qualitative research, common limitations include the following:

- Lack of generalizability of findings (not the goal of qualitative research, but still worth mentioning as a limitation)

- Inability to draw causal conclusions (again, not the goal of qualitative research, but still worth mentioning)

- Researcher bias/subjectivity (especially if there is only one coder)

- Limitations in participants’ ability/willingness to share or describe their experiences

- Any factors that might limit the rigor of data collection or analysis procedures

Common Examples of Delimitations

As noted above, the two most common sources of delimitations in both quantitative and qualitative research include the following:

- Inclusion/exclusion criteria (or how you define your population of interest)

- Research questions or problems you’ve chosen to examine

Several other common sources of delimitations include the following:

- Theoretical framework or perspective adopted

- Methodological framework or paradigm chosen (e.g., quantitative, qualitative, or mixed-methods)

- In quantitative research, the variables you’ve chosen to measure or manipulate (as opposed to others)

Whether you’re conducting a quantitative or qualitative study, you will (hopefully!) have chosen your research design because it is well suited to the questions you’re hoping to answer. Because these questions define the boundaries or scope of your project and thus point to its delimitations, your research design itself will also be related to these delimitations.

Questions to Ask Yourself

As you are considering the limitations and delimitations of your project, it can be helpful to ask yourself a few different questions.

Questions to help point out your study’s limitations:

1. If I had an unlimited budget, unlimited amounts of time, access to all possible populations, and the ability to manipulate as many variables as I wanted, how would I design my study differently to be better able to answer the questions I want to answer? (The ways in which your study falls short of this will point to its limitations.)

2. Are there design issues that get in the way of my being able to draw causal conclusions?

3. Are there sampling issues that get in the way of my being able to generalize my findings?

4. Are there issues related to the measures I’m using or the methods I’m using to collect data? Do I have concerns about participants telling the truth or being able to provide accurate responses to my questions?

5. Are there any other factors that might limit my study’s internal or external validity?

Questions that help point out your study’s delimitations:

1. What are my exclusion criteria? Who did I not include in my study, and why did I make this choice?

2. What questions did I choose not to address in my study? (Of course, the possibilities are endless here, but consider related questions that you chose not to address.)

3. In what ways did I narrow the scope of my study in order to hone in on a particular issue or question?

4. What other methodologies did I not use that might have allowed me to answer slightly different questions about the same topic?

How to Write About Limitations and Delimitations

Remember, having limitations and delimitations is not a bad thing. They’re present in even the most rigorous research. The important thing is to be aware of them and to acknowledge how they may impact your findings or the conclusions you can draw.

In fact, writing about them and acknowledging them gives you an opportunity to demonstrate that you can think critically about these aspects of your study and how they impact your findings, even if they were out of your control.

Keep in mind that your study’s limitations will likely point to important directions for future research. Therefore, when you’re getting ready to write about your recommendations for future research in your discussion, remember to refer back to your limitations section!

As you write about your delimitations in particular, remember that they are not weaknesses, and you don’t have to apologize for them. Good, strong research projects have clear boundaries. Also, keep in mind that you are the researcher and you can choose whatever delimitations you want for your study. You’re in control of the delimitations. You just have to be prepared—both in your discussion section and in your dissertation defense itself—to justify the choices you make and acknowledge how these choices impact your findings.

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