What is the dependent variable and what is independent variable?

Question

Is d dimer assay more accurate at ruling out deep vein thrombosis compared to ultrasound? and experiment is ultrasound currently used-control group and d dimer test experimental group testing ability to rule out deep vein thrombosis accurately. What is the dependent variable and what is independent variable?

Answer 1

Variables only apply to experimental investigations and are separated into two parts: the independent variable (cause) and the dependent variable (effect). In an experiment, the researcher is looking for the possible effect on the dependent variable that might be caused by changing the independent variable. Basically what you are trying to measure is considered your variables (DD vs UTZ).

Hypothesis: Appropriate use of D-dimer testing can minimize over-utilization of venous duplex ultrasound in a contemporary high-volume hospital. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4511119/  

Independent: Represents the quantity being manipulated in an experiment (what you can control or what you are researching). In this case, how often one is being used vs the other. For whatever reason, the provider orders the tests as a preference or because they believe one is better over the other, or maybe because one can detect the exact location of the DVT and the other just detects the presence of it. Therefore, your dependent variable is the use of the lab or radiologic exam.

Dependent: Represents the quantity whose value depends on how the independent variable is manipulated (what you cannot control, but results can depend on other factors). In this case, reasons a D-dimer is being done vs an ultrasound (to detect DVT). This variable cannot be changed but can be controlled. A hospital or doctor may choose one over the other because they both produce 95% accuracy in detecting DVT. Therefore, your independent variable is the detection of DVT. This is the variable being tested or measured and is usually held constant.

Example: A scientist wants to see if the brightness of light has any effect on a moth being attracted by the light. The brightness of the light that is controlled by the scientist is the independent variable. How the moth reacts to the different light levels is the dependent variable. How to tell the variables can be viewed as cause and effect: If the independent variable is changed, then the effect is seen in the dependent variable.