# Xplain the relationship between variables and controls in an experiment

### Experiment - Wikipedia

Cause and effect relationships explain why things happen and allow you to An experiment usually has three kinds of variables: independent, dependent, and Controlled variables are quantities that a scientist wants to remain constant, and . Examples of Independent and Dependent Variables in Experiments the relationship between the dependent and independent variables. This lesson explores the terminology of experimental design. What are Linear & Nonlinear Relationships in Data Graphs. Researcher.

• Variables in Your Science Fair Project
• Controlled experiments

Discrete variables are ones that have a few, distinct values. Something can be either on or off, present or absent, or have only several countable possibilities. A kitchen light can be on or off or a person may have blue, brown, green or hazel eyes. Independent Variable An independent variable is a variable that you can control. One way to explain it to a child is that it is the variable that the child can change during the experiment.

For example, in an experiment on the effect of light on plant growth, the child can control how much light a plant receives. He can put one plant near a window and another plant in a dark closet. Sciencing Video Vault Dependent Variable A dependent variable is the variable that you observe and measure. You have no control over the dependent variable; you want to observe what happens to the dependent variable when you change the independent variable.

### What Are Independent & Dependent Variables in Science for Kids? | Sciencing

For example, if the child is testing the effects of light on plant growth, how much the plant grows after some period of time would be the dependent variable. The child can measure how much the plant in the closet grows relative to how much the plant near the window grows.

Random assignment is uncommon. In medicine and the social sciencesthe prevalence of experimental research varies widely across disciplines. When used, however, experiments typically follow the form of the clinical trialwhere experimental units usually individual human beings are randomly assigned to a treatment or control condition where one or more outcomes are assessed.

There are various differences in experimental practice in each of the branches of science. For example, agricultural research frequently uses randomized experiments e. History of experiments One of the first methodical approaches to experiments in the modern sense is visible in the works of the Arab mathematician and scholar Ibn al-Haytham.

## Experiment

He conducted his experiments in the field of optics - going back to optical and mathematical problems in the works of Ptolemy - by controlling his experiments due to factors such as self-criticality, reliance on visible results of the experiments as well as a criticality in terms of earlier results. He counts as one of the first scholars using an inductive-experimental method for achieving results. We should distinguish the properties of particulars, and gather by induction what pertains to the eye when vision takes place and what is found in the manner of sensation to be uniform, unchanging, manifest and not subject to doubt.

After which we should ascend in our inquiry and reasonings, gradually and orderly, criticizing premisses and exercising caution in regard to conclusions — our aim in all that we make subject to inspection and review being to employ justice, not to follow prejudice, and to take care in all that we judge and criticize that we seek the truth and not to be swayed by opinion.

We may in this way eventually come to the truth that gratifies the heart and gradually and carefully reach the end at which certainty appears; while through criticism and caution we may seize the truth that dispels disagreement and resolves doubtful matters.

For all that, we are not free from that human turbidity which is in the nature of man; but we must do our best with what we possess of human power. From God we derive support in all things. Furthermore, a critical view on the results and outcomes of earlier scholars is necessary: He should also suspect himself as he performs his critical examination of it, so that he may avoid falling into either prejudice or leniency.

In this process of critical consideration, the man himself should not forget that he tends to subjective opinions - through "prejudices" and "leniency" - and thus has to be critical about his own way of building hypotheses. He disagreed with the method of answering scientific questions by deduction - similar to Ibn al-Haytham - and described it as follows: Notably, he first ordered the scientific method as we understand it today.

There remains simple experience; which, if taken as it comes, is called accident, if sought for, experiment. The true method of experience first lights the candle [hypothesis], and then by means of the candle shows the way [arranges and delimits the experiment]; commencing as it does with experience duly ordered and digested, not bungling or erratic, and from it deducing axioms [theories], and from established axioms again new experiments.

For example, Galileo Galilei accurately measured time and experimented to make accurate measurements and conclusions about the speed of a falling body. Antoine Lavoisiera French chemist, used experiment to describe new areas, such as combustion and biochemistry and to develop the theory of conservation of mass matter.

A considerable amount of progress on the design and analysis of experiments occurred in the early 20th century, with contributions from statisticians such as Ronald FisherJerzy NeymanOscar KempthorneGertrude Mary Coxand William Gemmell Cochranamong others. Types of experiment[ edit ] Experiments might be categorized according to a number of dimensions, depending upon professional norms and standards in different fields of study.

In some disciplines e. The independent variable is manipulated by the experimenter, and the dependent variable is measured. The signifying characteristic of a true experiment is that it randomly allocates the subjects to neutralize experimenter bias, and ensures, over a large number of iterations of the experiment, that it controls for all confounding factors.

### Controlled experiments (article) | Khan Academy

Scientific control and Design of experiments A controlled experiment often compares the results obtained from experimental samples against control samples, which are practically identical to the experimental sample except for the one aspect whose effect is being tested the independent variable. A good example would be a drug trial. The sample or group receiving the drug would be the experimental group treatment group ; and the one receiving the placebo or regular treatment would be the control one.

In many laboratory experiments it is good practice to have several replicate samples for the test being performed and have both a positive control and a negative control. The results from replicate samples can often be averaged, or if one of the replicates is obviously inconsistent with the results from the other samples, it can be discarded as being the result of an experimental error some step of the test procedure may have been mistakenly omitted for that sample.

Most often, tests are done in duplicate or triplicate. A positive control is a procedure similar to the actual experimental test but is known from previous experience to give a positive result. A negative control is known to give a negative result. The positive control confirms that the basic conditions of the experiment were able to produce a positive result, even if none of the actual experimental samples produce a positive result.

Experimental Design: Variables, Groups, and Controls

The negative control demonstrates the base-line result obtained when a test does not produce a measurable positive result. Most often the value of the negative control is treated as a "background" value to subtract from the test sample results. Sometimes the positive control takes the quadrant of a standard curve. An example that is often used in teaching laboratories is a controlled protein assay.

Students might be given a fluid sample containing an unknown to the student amount of protein. It is their job to correctly perform a controlled experiment in which they determine the concentration of protein in the fluid sample usually called the "unknown sample". The teaching lab would be equipped with a protein standard solution with a known protein concentration. Students could make several positive control samples containing various dilutions of the protein standard. Negative control samples would contain all of the reagents for the protein assay but no protein.

In this example, all samples are performed in duplicate.

The assay is a colorimetric assay in which a spectrophotometer can measure the amount of protein in samples by detecting a colored complex formed by the interaction of protein molecules and molecules of an added dye.

In the illustration, the results for the diluted test samples can be compared to the results of the standard curve the blue line in the illustration to estimate the amount of protein in the unknown sample. Controlled experiments can be performed when it is difficult to exactly control all the conditions in an experiment.

In this case, the experiment begins by creating two or more sample groups that are probabilistically equivalent, which means that measurements of traits should be similar among the groups and that the groups should respond in the same manner if given the same treatment. This equivalency is determined by statistical methods that take into account the amount of variation between individuals and the number of individuals in each group.

In fields such as microbiology and chemistrywhere there is very little variation between individuals and the group size is easily in the millions, these statistical methods are often bypassed and simply splitting a solution into equal parts is assumed to produce identical sample groups. Once equivalent groups have been formed, the experimenter tries to treat them identically except for the one variable that he or she wishes to isolate. Human experimentation requires special safeguards against outside variables such as the placebo effect.

Such experiments are generally double blindmeaning that neither the volunteer nor the researcher knows which individuals are in the control group or the experimental group until after all of the data have been collected.

This ensures that any effects on the volunteer are due to the treatment itself and are not a response to the knowledge that he is being treated. In human experiments, researchers may give a subject person a stimulus that the subject responds to. The goal of the experiment is to measure the response to the stimulus by a test method. Original map by John Snow showing the clusters of cholera cases in the London epidemic of In the design of experimentstwo or more "treatments" are applied to estimate the difference between the mean responses for the treatments.

For example, an experiment on baking bread could estimate the difference in the responses associated with quantitative variables, such as the ratio of water to flour, and with qualitative variables, such as strains of yeast.