Dissertations can suffer from a wide range of potential threats to internal validity , which have been discussed extensively in the literature e. Independent and dependent variables A variable is not only something that we measure , but also something that we can manipulate and something we can control for. Employed, Unemployed Dichotomous variables are nominal variables that have just two categories. How often do British university students use Facebook each week? What proportion of British male and female university students use the top 5 social networks? They have a number of characteristics:. Nominal variables have two or more categories.
The examples above highlight a desire to capture what we mean about something through the use of just a few words often only one or two words. The appropriate structure for each of these quantitative research questions is set out below:. This would help you to avoid a potentially more time consuming and expensive piece of research looking into a potential problem or issue that actually doesn’t exist. Opinion about watching television Level: For example, we cannot say that the response, They are OK , is twice as positive as the response, Not very much. The dependent variable is simply that; a variable that is dependent on an independent variable s. Even whether this is desired, there are additional problems of bias and transferability or validity [see the section on Research Quality for more information on research strategies, sampling techniques, and bias ].
These dichotomous variables could address questions like:.
Internal validity | Lærd Dissertation
Constructs can be represented by a wide range of variables. For example, you may choose to select only those units to be included in your sample that you feel will exhibit the problem or issue you are interested in finding.
Weekly photo uploads on Facebook 2. However, variablles a descriptive research question is not simply interested in measuring the dependent variable in its entirety, but a particular component of the dependent variable.
Before we explain the relationship between extraneous variables and confounding variableslet’s look at some examples of extraneous variables:.
The purpose of this article is to introduce you to the three different types of quantitative research question i. These nominal variables could address questions like: Take the following examples: When it comes to Likert scales, as highlighted in the previous example, there can be some disagreement over whether these should be considered ordinal variables or continuous variables [see the section: What percentage of American men and women exceed their daily calorific allowance?
The example descriptive research questions discussed above are written out in full below: Salary and benefits 3.
After all, the purpose of the dissertation is duplicationwhere you are, in effect, re-testing the study in the main journal article to see if the same or similar findings are found. The examples illustrate the difference between the use of a single group e. In such cases, it may be better to refer to the variable gender as sex.
If this problem or issue does not exist even in your biased sampleit is unlikely to be present if diswertation selected a relatively unbiased sample whether using another non-probability sampling technique; or even a probability sampling technique. When a Likert scale has five values e. Euthanasia “The painless killing of a patient suffering from an incurable and painful disease or in an irreversible coma” Oxford Dictionaries, Ultimately, you choose which categories or levels to include and how many categories or levels there should be.
Job satisfaction Independent variable: To provide a brief explanation; a variable is not only something that you measurebut also something that you can manipulate and control for.
Moderator Analysis with a Dichotomous Moderator using SPSS Statistics
What do I have to think aboutas well as an overview article on types of variableswhich will help to familiarise you with terms such as dependent and independent variableas well as categorical and continuous variables [see the article: Whilst constructs are sometimes mistaken for variablesthey are not variables.
In the second example, the dependent variable diesertation Facebook usage per week. As mentioned, for researchers following a quantitative research design, non-probability sampling techniques can often be viewed as an inferior alternative to probability sampling techniques.
Therefore, the tutor decides to investigate the effect of revision time and intelligence on the test performance of the students. Take the following examples:. Since a conceptual definition only provides the platform for the operational definition that is used to empirically measure constructs, we discuss about translating constructs into operational definitions in the next section. We discuss the two groups of variable, as well as these potential ambiguities, in the sections that follow:.
Some examples of ratio variables are: Yes I do or No I don’t Dichotomous variable: When following a qualitative research designnon-probability sampling techniques, such as purposive samplingcan provide researchers with strong theoretical reasons for their choice of units or cases to be included in their sample.
Second, we explain what dependent and independent variables are. If you varkables taking on Route A: This is because they view gender as having a number of categories, including male, female, bisexual and transsexual.