text: What Variables Can Change in an Experiment? - BartlesVilleSchools
  A variable is any factor, attribute, or circumstance that can exist in varying quantities or forms. Variables in an experiment are typically of three types: independent, dependent, and controlled. The independent variable is the one that the scientist alters. In an experiment to find out how much ice melts when water is put in a glass, the amount of ice used as starting material is an independent variable because it can vary from trial to trial. The amount of time that the water is left in the glass is the dependent variable because it can only take on certain values. Whether or not the water freezes depends on both the amount of ice and the temperature outside the glass. The control variable is a term used by statisticians and researchers who study human behavior to refer to a factor that remains constant during an experiment but that can be altered to see how it affects the outcome.
  Independent variables can be changed in two ways: directly through additional experiments (such as adding more water) or indirectly, such as changing the length of time that water is frozen before being added to the glass. Dependent variables cannot be changed after the experiment has been conducted so they must be recorded before the start of the study.
  Controlled variables are important tools for scientists. They allow us to examine what causes what effects.
  What is the factor that a scientist changes during an experiment?
  What are the parts of an experiment that can be changed?
  Why are the factors in an experiment called variables?
  In an experiment, a variable is a factor that changes. The independent variable is the variable that the scientist tests and changes. As a result of the independent variable being changed, the dependent variable will also change.
  During an experiment, scientists change one or more factors to see how they affect the outcome. For example, if they want to know how high something can be lifted, they would lift it until it cannot be lifted any further. This is an experimental method called "lifting trials." In this case, the thing being lifted is called the "load." The amount of weight used in lifting trials should be as close to the expected load as possible so that there is no question about how much weight was actually used. For example, if the expected load is 100 pounds, then 20 pounds would be a reasonable test weight.
  Scientists usually change only one variable at a time so that they can determine what role it plays in the outcome of their experiments. If they try changing two variables at once, they would not be able to tell which variable had the most influence on the outcome.
  For example, an experiment might test how quickly plants grow under different conditions (such as different amounts of water or fertilizer).
  Variables are the factors that change in an experiment. Independent variables are factors that are controllable by the experimenter and that may affect the outcome of the experiment.
  Dependent variables are responses that are affected by the intervention under study. For example, if a researcher wanted to know how much water is needed to fill a swimming pool, the response would be the size of the pool after filling it with water. The amount of water added is the treatment, and the size of the pool is the outcome. Note that both the treatment and the outcome must be measured to determine whether the result is significant.
  Controlled variables are factors that act as controls for other variables. In the previous example, if the researcher was also counting the number of strokes it takes to fill the pool, this would be a controlled variable because it allows them to control for things such as human ability. Without a control group, it's impossible to know what percentage increase or decrease in performance is due to the treatment rather than other factors such as fatigue from using up too much energy during the first trial.
  Changes may also be made to materials used in an experiment.
  In other words, scientists perform experiments to observe or quantify whether changes to one thing influence something else to fluctuate in a predictable fashion. For example, if you were to conduct an experiment to see how much water is needed to grow peas, the variable for your experiment would be the amount of water given to the plants. The quantity of water available to the plant will vary depending on many factors such as the type of soil they are grown in and how often they are watered, among others.
  Variables can be divided up into two categories: constant and non-constant variables. Constant variables do not change during the course of an experiment. Examples of constant variables include age, gender, and body weight. Non-constant variables change over time. An example of a non-constant variable is stress levels. Stress levels increase as the experiment progresses because the animals become more stressed by being held in confinement longer.
  The goal of an experiment is to identify relationships between different variables. Scientists use statistical methods to analyze their data. One such method is regression analysis. In this case study, we will examine why farmers use horses to plow fields. First, we need to understand what conditions must be met for this method to be effective. Horses must be available and willing to work for pay.
  Variables in research are any attributes that can have many values, such as height, age, species, or exam score. In scientific research, we frequently seek to investigate the impact of one variable on another. The effect is the dependent variable. Its value fluctuates in response to changes in the independent variable. For example, if we were looking at how exercise affects blood glucose levels, the amount of glucose in the blood would be the dependent variable and exercise time would be the independent variable.
  Independent and dependent variables are important concepts to understand when doing research. Independent variables are factors that can be changed to see what effect it has on the dependent variable. Dependent variables are those things that change due to some other factor(s). For example, if I were to increase the amount of exercise I do, my blood glucose level would go up. This is because increased activity causes me to burn more calories per day than I eat, so there's less glucose in my bloodstream. This is why dependent variables need to be controlled when investigating effects of independent variables on them.
  There are two ways that researchers test theories about relationships between variables: experimentally and observationally. In experimental studies, scientists try out different conditions (values of the independent variable) to see which results they get (the dependent variable). For example, researchers might give some participants an exercise program and see how their blood glucose levels compare with participants who don't receive an exercise program.