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Share Flipboard Email. Todd Helmenstine. Todd Helmenstine is a science writer and illustrator who has taught physics and math at the college level. He holds bachelor's degrees in both physics and mathematics. Updated January 13, Key Takeaways: Control vs.
Experimental Group The control group and experimental group are compared against each other in an experiment. The only difference between the two groups is that the independent variable is changed in the experimental group.
The independent variable is "controlled" or held constant in the control group. A single experiment may include multiple experimental groups, which may all be compared against the control group. The purpose of having a control is to rule out other factors which may influence the results of an experiment. Not all experiments include a control group, but those that do are called "controlled experiments. A placebo isn't a substitute for a control group because subjects exposed to a placebo may experience effects from the belief they are being tested.
Featured Video. Cite this Article Format. Helmenstine, Todd. Independent Variable Definition and Examples. Understanding Simple vs Controlled Experiments. Dependent Variable Definition and Examples. What Is an Experiment? No problem. We are always here for you. Scribbr specializes in editing study-related documents. We proofread:.
You can find all the citation styles and locales used in the Scribbr Citation Generator in our publicly accessible repository on Github. Frequently asked questions See all. Home Frequently asked questions Do experiments always need a control group? Do experiments always need a control group? What is sampling? Reliability and validity are both about how well a method measures something: Reliability refers to the consistency of a measure whether the results can be reproduced under the same conditions.
Validity refers to the accuracy of a measure whether the results really do represent what they are supposed to measure.
What is the difference between internal and external validity? What is experimental design? To design a controlled experiment, you need: A testable hypothesis At least one independent variable that can be precisely manipulated At least one dependent variable that can be precisely measured When designing the experiment, you decide: How you will manipulate the variable s How you will control for any potential confounding variables How many subjects or samples will be included in the study How subjects will be assigned to treatment levels Experimental design is essential to the internal and external validity of your experiment.
What are independent and dependent variables? For example, in an experiment about the effect of nutrients on crop growth: The independent variable is the amount of nutrients added to the crop field.
The dependent variable is the biomass of the crops at harvest time. What is the difference between quantitative and categorical variables? What is the difference between discrete and continuous variables? Discrete and continuous variables are two types of quantitative variables : Discrete variables represent counts e.
Continuous variables represent measurable amounts e. What is a confounding variable? How do I decide which research methods to use? If you want to measure something or test a hypothesis , use quantitative methods. If you want to explore ideas, thoughts and meanings, use qualitative methods.
If you want to analyze a large amount of readily-available data, use secondary data. If you want data specific to your purposes with control over how it is generated, collect primary data. If you want to establish cause-and-effect relationships between variables , use experimental methods. If you want to understand the characteristics of a research subject, use descriptive methods.
What is mixed methods research? What is internal validity? What are threats to internal validity? What is the difference between a longitudinal study and a cross-sectional study? What are the pros and cons of a longitudinal study? What is an example of a longitudinal study?
How long is a longitudinal study? Why do a cross-sectional study? What are the disadvantages of a cross-sectional study? What is external validity?
What are the two types of external validity? What are threats to external validity? Why are samples used in research? When are populations used in research? What is sampling error? What is sampling bias? Why is sampling bias important? What are some types of sampling bias? How do you avoid sampling bias? What is probability sampling? What is non-probability sampling?
Why are independent and dependent variables important? What is an example of an independent and a dependent variable? The type of soda — diet or regular — is the independent variable. The level of blood sugar that you measure is the dependent variable — it changes depending on the type of soda. Can a variable be both independent and dependent? Can I include more than one independent or dependent variable in a study?
Why do confounding variables matter for my research? What is the difference between confounding variables, independent variables and dependent variables? How do I prevent confounding variables from interfering with my research?
What is data collection? What are the benefits of collecting data? When conducting research, collecting original data has significant advantages: You can tailor data collection to your specific research aims e. What is operationalization? What is hypothesis testing? What are the main qualitative research approaches? There are five common approaches to qualitative research : Grounded theory involves collecting data in order to develop new theories.
Ethnography involves immersing yourself in a group or organization to understand its culture. Narrative research involves interpreting stories to understand how people make sense of their experiences and perceptions. Action research links theory and practice in several cycles to drive innovative changes.
How do you analyze qualitative data? There are various approaches to qualitative data analysis , but they all share five steps in common: Prepare and organize your data. Review and explore your data.
Develop a data coding system. Assign codes to the data. Identify recurring themes. What is a Likert scale? Are Likert scales ordinal or interval scales? What is the difference between a control group and an experimental group? What is blinding? What is the difference between single-blind, double-blind and triple-blind studies?
In a single-blind study , only the participants are blinded. In a double-blind study , both participants and experimenters are blinded. In a triple-blind study , the assignment is hidden not only from participants and experimenters, but also from the researchers analyzing the data. Why is blinding important? What is a quasi-experiment? When should I use a quasi-experimental design? What is simple random sampling? What is an example of simple random sampling?
When should I use simple random sampling? However, it can sometimes be impractical and expensive to implement, depending on the size of the population to be studied, If you have a list of every member of the population and the ability to reach whichever members are selected, you can use simple random sampling.
What is cluster sampling? The clusters should ideally each be mini-representations of the population as a whole. What are the types of cluster sampling? In single-stage sampling , you collect data from every unit within the selected clusters. In double-stage sampling , you select a random sample of units from within the clusters. In multi-stage sampling , you repeat the procedure of randomly sampling elements from within the clusters until you have reached a manageable sample.
What are some advantages and disadvantages of cluster sampling? What is stratified sampling? When should I use stratified sampling? Can I stratify by multiple characteristics at once? What is systematic sampling? How do I perform systematic sampling? There are three key steps in systematic sampling : Define and list your population , ensuring that it is not ordered in a cyclical or periodic order. Decide on your sample size and calculate your interval, k , by dividing your population by your target sample size.
Choose every k th member of the population as your sample. How can you tell if something is a mediator? Why should you include mediators and moderators in a study?
What is a control variable? Why are control variables important? What is random assignment? How do you randomly assign participants to groups? When do you use random assignment? Can you use a between- and within-subjects design in the same study? What are the pros and cons of a between-subjects design?
Advantages: Prevents carryover effects of learning and fatigue. Shorter study duration. Disadvantages: Needs larger samples for high power. Uses more resources to recruit participants, administer sessions, cover costs, etc. Individual differences may be an alternative explanation for results. What are the pros and cons of a within-subjects design? Advantages: Only requires small samples, Statistically powerful, Removes the effects of individual differences on the outcomes.
Disadvantages: Internal validity threats reduce the likelihood of establishing a direct relationship between variables, Time-related effects, such as growth, can influence the outcomes, Carryover effects mean that the specific order of different treatments affect the outcomes. What is a factorial design? What are the types of extraneous variables?
Experimenter effects : unintentional actions by researchers that influence study outcomes. What are the requirements for a controlled experiment? Controlled experiments require: A control group that receives a standard treatment, a fake treatment, or no treatment. Random assignment of participants to ensure the groups are equivalent. What are explanatory and response variables? The difference between explanatory and response variables is simple: An explanatory variable is the expected cause, and it explains the results.
A response variable is the expected effect, and it responds to other variables. How do explanatory variables differ from independent variables? How do you plot explanatory and response variables on a graph?
If you have quantitative variables , use a scatterplot or a line graph. If your response variable is categorical, use a scatterplot or a line graph.
If your explanatory variable is categorical, use a bar graph. Is random error or systematic error worse? How do you avoid measurement errors? What is a correlation? In a controlled experiment, two identical experiments are carried out: in one of them, the treatment or tested factor experimental group is applied; whereas in the other group control , the tested factor is not applied.
A good example for us, orthodontists, is the assessment of the influence of medicine over orthodontic tooth movement. In these cases, it is important to examine if the supposed effects of the applied drug are produced only by the drug. In this situation, identical groups of patients or animals are compared, one of them receives the drug and the other receives a placebo or, in many cases, does not receive any drug control group.
In order to avoid bias, it is always important to prevent not only the researchers, but also the individuals who will receive the medicine from knowing which group receives the real drug.
In Orthodontics, as in any specialty in the Health field, it is difficult to establish a control group for clinical studies, given that many ethical implications are involved. A good example to demonstrate this situation is the proposal of a study focused on the assessment of a new method for skeletal Class II malocclusion treatment of patients in craniofacial growth.
The ideal control group, in this case, would comprise patients with the same characteristics of those in the experimental group, including age, race, maturation stage, same tendency for craniofacial growth. However, to be in the control group, patients should not be orthopedically treated, precisely in the ideal phase for treatment. In these situations, an ethical issue arises: How can we carry out an experiment without causing any damage to patients? In situations like these, it is acceptable that the patients in the control group be subjected to procedures already established in literature 3 - which, in this particular case, would consist of treatment performed with extraoral appliances considered as gold standard in the treatment of malocclusion.
Although not ideal, given that we would not have a control group without any involved factor, this approach meets the ethical requirements that currently surround us. A more delicate situation involves studies that use computed tomography as a method of diagnosis.
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