High quality dissertations clearly distinguish between concepts, constructs and variables. They do this so that the reader knows the difference between the broad concept/construct that you are interested in (e.g., gender) and the variables that you use to measure these concepts/constructs (e.g., whether an individual is male or female; or more broadly, male, female, bisexual, homosexual, transsexual, etc.). Broadly speaking, we tend to look at concepts, constructs and variables in different ways depending on whether we are taking on a quantitative or qualitative dissertation. The reasons for this range from the research paradigms underpinning these broad types of research (i.e., quantitative and qualitative research) through to the way that we examine/measure what we are studying, analyse the information/data we have collected, and even the way that we present such findings/results on the page.
At this point, the Lærd Dissertation site focuses on the use of concepts, constructs and variables in quantitative research. Therefore, if you are unsure what constructs are, their purpose in dissertations, and how they should be used, you may want to start with the article: Constructs in quantitative dissertations. You can also learn more about variables in the section on Types of variables. If you would like to see us launch a similar section for qualitative research in the short-term, please leave feedback.