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Encyclopedia > Experiment

In the scientific method, an experiment (Latin: ex- periri, "of (or from) trying") is a set of observations performed in the context of solving a particular problem or question, to retain or falsify a hypothesis or research concerning phenomena. The experiment is a cornerstone in the empirical approach to acquiring deeper knowledge about the physical world. Scientific method is a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. ... For other uses, see Latin (disambiguation). ... For other uses, see Observation (disambiguation). ... Look up Problem in Wiktionary, the free dictionary. ... Wikipedia does not yet have an article with this exact name. ... Look up Hypothesis in Wiktionary, the free dictionary. ... This article is about the concept. ... For other uses, see Phenomena (disambiguation). ... In philosophy generally, empiricism is a theory of knowledge emphasizing the role of experience, especially sensory perception, in the formation of ideas, while discounting the notion of innate ideas. ... This article needs additional references or sources for verification. ...

Contents

Design of experiments

Main article: Design of experiments
  1. That the independent variable is the only factor that varies systematically in the experiment; in other words, that the experiment is appropriately controlled - that confounding variables are eliminated; and
  2. That the dependent variable truly reflects the phenomenon under study (a question of validity) and that the variable can be measured accurately (i.e., that various types of experimental error, such as measurement error can be eliminated).

In a pure application of the scientific method, hypotheses are tested by critical experiments: ones that can falsify the hypothesis in the case of a non-result (i.e., an experiment showing that the independent variable did not affect the dependent variable as predicted). Such pure applications are rare, however, in part because a result can sometimes be challenged on the basis that an experiment was not sufficiently controlled, that the dependent variable was not valid, or that various forms of error compromised the experiment. The scientific method, as a result, builds in the need for reproducibility (usually termed replication) and convergent evidence (see also: external validity).I want to kiss your butt but its to late The first statistician to consider a methodology for the design of experiments was Sir Ronald A. Fisher. ... It has been suggested that this article or section be merged with scientific control. ... In statistics, a spurious relationship (or, sometimes, spurious correlation) is a mathematical relationship in which two occurrences have no logical connection, yet it may be implied that they do, due to a certain third, unseen factor (referred to as a confounding factor or lurking variable). The spurious relationship gives an... In psychology, validity has two distinct fields of application. ... Measurement is the determination of the size or magnitude of something. ... Scientific method is a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. ... In the sciences, an experimentum crucis, or critical experiment, is an experiment capable of decisively determining whether or not a particular hypothesis or theory is correct. ... Falsifiability (or refutability or testability) is the logical possibility that an assertion can be shown false by an observation or a physical experiment. ... This article is in need of attention from an expert on the subject. ... In convergent validity, we examine the degree to which the operationalization is similar to (converges on) other operationalizations that it theoretically should be similar to. ... External validity is a term used in scientific research. ...


The design of experiments attempts to balance the requirements and limitations of the field of science in which one works so that the experiment can provide the best conclusion about the hypothesis being tested. In some sciences, such as physics and chemistry, it is relatively easy to meet the requirements that all measurements be made objectively, and that all conditions can be kept controlled across experimental trials. On the other hand, in other cases such as biology, and medicine, it is often hard to ensure that the conditions of an experiment are performed consistently; and in the social sciences, it may even be difficult to determine a method for measuring the outcomes of an experiment in an objective manner. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... For other uses, see Chemistry (disambiguation). ... For the song by Girls Aloud see Biology (song) Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: βίος, bio, life; and λόγος, logos, speech lit. ... For the chemical substances known as medicines, see medication. ... The social sciences are a group of academic disciplines that study human aspects of the world. ...


For this reason, sciences such as physics and several other fields of natural science are sometimes informally referred to as "hard sciences", while social sciences are sometimes informally referred to as "soft sciences"; in an attempt to capture the idea that objective measurements are often far easier in the former, and far more difficult in the latter. The Michelson–Morley experiment was used to disprove that light propagated through a luminiferous aether. ... The social sciences are a group of academic disciplines that study human aspects of the world. ...


In addition, in the social sciences, the requirement for a "controlled situation" may actually work against the utility of the hypothesis in a more general situation. When the desire is to test a hypothesis that works "in general", an experiment may have a great deal of internal validity, in the sense that it is valid in a highly controlled situation, while at the same time lack external validity when the results of the experiment are applied to a real world situation. One of the reasons why this may happen is the Hawthorne effect; another is that partial equilibrium effects may not persist in general equilibrium. The Hawthorne effect refers to a phenomenon of observing workers behavior or their performance and changing it temporarily. ... Definition A partial equilibrium is a special case of the general economic equilibrium, where the clearance on the market of some specific goods is obtained independently from prices and quantities demanded and supplied on other goods markets. ... General Equilibrium (linear) supply and demand curves. ...


As a result of these considerations, experimental design in the "hard" sciences tends to focus on the elimination of extraneous effects, while experimental design in the "soft" sciences focuses more on the problems of external validity, often through the use of statistical methods. Occasionally events occur naturally from which scientific evidence can be drawn, which is the basis for natural experiments. In such cases the problem of the scientist is to evaluate the natural "design". This article is about the field of statistics. ... A natural experiment is a naturally occurring instance of observable phenomena which approach or duplicate a scientific experiment. ...


Controlled (Laboratory) experiments

Main article: Experimental control

Many hypotheses in sciences such as physics can establish causality by noting that, until some phenomenon occurs, nothing happens; then when the phenomenon occurs, a second phenomenon is observed. But often in science, this situation is difficult to obtain. It has been suggested that this article or section be merged with scientific control. ...


For example, in the old joke, someone claims that they are snapping their fingers "to keep the tigers away"; and justifies this behavior by saying "see - its working!" While this "experiment" does not falsify the hypothesis "snapping fingers keeps the tigers away", it does not really support the hypothesis - not snapping your fingers keeps the tigers away as well.


To demonstrate a cause and effect hypothesis, an experiment must often show that, for example, a phenomenon occurs after a certain treatment is given to a subject, and that the phenomenon does not occur in the absence of the treatment. (See Baconian method.) The Baconian method is the investigative method developed by Francis Bacon. ...

Standard curve
Standard curve

A controlled experiment generally compares the results obtained from an experimental sample against a control sample, which is practically identical to the experimental sample except for the one aspect whose effect is being tested. A good example would be a drug trial. The sample or group receiving the drug would be the experimental one; and the one receiving the placebo 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 that is very similar to the actual experimental test but which 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. The negative control demonstrates the base-line result obtained when a test does not produce a measurable positive result; often the value of the negative control is treated as a "background" value to be subtracted from the test sample results. Sometimes the positive control takes the form of a standard curve. Illustration for positive control, negative control, and replicate samples in an experiment. ... Illustration for positive control, negative control, and replicate samples in an experiment. ... Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... A scientific control augments integrity in experiments by isolating variables as dictated by the scientific method in order to make a conclusion about such variables. ... A standard curve is a quantitative research tool, a method of plotting assay data that is used to determine the concentration of a substance, particularly proteins and DNA. The assay is first performed with various known concentrations of a substance similar to that being measured. ...


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 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) in order to determine an estimate of the amount of protein in the unknown sample. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... An assay is a procedure where the concentration of a component part of a mixture is determined. ... In physics, spectrophotometry is the quantitative study of spectra. ...


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 chemistry, where 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. This article is about the field of statistics. ... For other uses, see Number (disambiguation). ... An agar plate streaked with microorganisms Microbiology is the study of microorganisms, which are unicellular or cell-cluster microscopic organisms. ... For other uses, see Chemistry (disambiguation). ... Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ...


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 blind, meaning 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 has 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. Human experimentation involves medical experiments performed on human beings. ...


In human experiments, a subject (person) may be given a stimulus to which he or she should respond. The goal of the experiment is to measure the response to a given stimulus. In biostatistics or psychological statistics, a research subject is any organism (animal or plant) that is observed for purposes of research. ... Stimulation is the irritating action of various agents (stimuli) on muscles, nerves, or a sensory end organ, by which activity is evoked; especially, the nervous impulse produced by various agents on nerves, or a sensory end organ, by which the part connected with the nerve is thrown into a state... Measurement is the estimation of the magnitude of some attribute of an object, such as its length or weight, relative to a unit of measurement. ...


Natural experiments

Main article: Natural experiment

The term "experiment" usually implies a controlled experiment, but sometimes controlled experiments are prohibitively difficult or impossible. In this case researchers resort to natural experiments, also called quasi-experiments. Natural experiments rely solely on observations of the variables of the system under study, rather than manipulation of just one or a few variables as occurs in controlled experiments. To the degree possible, they attempt to collect data for the system in such a way that contribution from all variables can be determined, and where the effects of variation in certain variables remain approximately constant so that the effects of other variables can be discerned. The degree to which this is possible depends on the observed correlation between explanatory variables in the observed data. When these variables are not well correlated, natural experiments can approach the power of controlled experiments. Usually, however, there is some correlation between these variables, which reduces the reliability of natural experiments relative to what could be concluded if a controlled experiment were performed. Also, because natural experiments usually take place in uncontrolled environments, variables from undetected sources are neither measured nor held constant, and these may produce illusory correlations in variables under study. A natural experiment is a naturally occurring instance of observable phenomena which approach or duplicate a scientific experiment. ... In computer science and mathematics, a variable is a symbol denoting a quantity or symbolic representation. ... For other uses, see System (disambiguation). ... Positive linear correlations between 1000 pairs of numbers. ... In mathematics, an independent variable is any of the arguments, i. ...


Much research in several important science disciplines, including economics, political science, geology, paleontology, ecology, meteorology, and astronomy, relies on quasi-experiments. For example, in astronomy it is clearly impossible, when testing the hypothesis "suns are collapsed clouds of hydrogen", to start out with a giant cloud of hydrogen, and then perform the experiment of waiting a few billion years for it to form a sun. However, by observing various clouds of hydrogen in various states of collapse, and other implications of the hypothesis (for example, the presence of various spectral emissions from the light of stars), we can collect data we require to support the hypothesis. An early example of this type of experiment was the first verification in the 1600s that light does not travel from place to place instantaneously, but instead has a measurable speed. Observation of the appearance of the moons of Jupiter were slightly delayed when Jupiter was farther from Earth, as opposed to when Jupiter was closer to Earth; and this phenomenon was used to demonstrate that the difference in the time of appearance of the moons was consistent with a measurable speed of light. A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Face-to-face trading interactions on the New York Stock Exchange trading floor. ... The Politics series Politics Portal This box:      Political Science is the field concerning the theory and practice of politics and the description and analysis of political systems and political behaviour. ... This article includes a list of works cited but its sources remain unclear because it lacks in-text citations. ... Paleontology, palaeontology or palæontology (from Greek: paleo, ancient; ontos, being; and λόγος, logos, knowledge) is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. ... For the journal, see Ecology (journal). ... // Meteorology (from Greek: μετέωρον, meteoron, high in the sky; and λόγος, logos, knowledge) is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. ... For other uses, see Astronomy (disambiguation). ...


Observational studies

Main article: Observational study

Observational studies are very much like controlled experiments except that they lack probabilistic equivalency between groups. These types of experiments often arise in the area of medicine where, for ethical reasons, it is not possible to create a truly controlled group. For example, one would not want to deny all forms of treatment for a life-threatening disease from one group of patients to evaluate the effectiveness of another treatment on a different group of patients. The results of observational studies are considered much less convincing than those of designed experiments, as they are much more prone to selection bias. Researchers attempt to compensate for this with complicated statistical methods such as propensity score matching methods (see hierarchy of evidence). See also quasi-empirical methods In statistics, the goal of an observational study is to draw inferences about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator. ... Selection bias is the error of distorting a statistical analysis by pre- or post-selecting the samples. ... The hierarchy of evidence reflects the relative weight given various types of scientific evidence. ... Quasi-empirical methods are applied in science and in mathematics. ...


Field experiments

Main article: Field experiment

Field experiments are so named in order to draw a contrast with laboratory experiments. Often used in the social sciences, and especially in economic analyses of education and health interventions, field experiments have the advantage that outcomes are observed in a natural setting rather than in a contrived laboratory environment. However, like natural experiments, field experiments suffer from the possibility of contamination: experimental conditions can be controlled with more precision and certainty in the lab. A field experiment applies the scientific method to experimentally examine an intervention in the real world (or as many experimental economists like to say, naturally-occurring environments) rather than in the laboratory. ...


Examples

MTT assay is a laboratory test and a standard colorimetric assay (an assay which measures changes in colour) for measuring cellular proliferation (cell growth). ...

Quotes

"We have to learn again that science without contact with experiments is an enterprise which is likely to go completely astray into imaginary conjecture." — Hannes Alfven
"Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality." — Nikola Tesla

A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... Hannes Olof Gösta Alfvén (May 30, 1908; Norrköping, Sweden - April 2, 1995; Djursholm, Sweden) was a Swedish electrical power engineer. ... This article is about the profession. ... For other meanings of mathematics or uses of math and maths, see Mathematics (disambiguation) and Math (disambiguation). ... An equation is a mathematical statement, in symbols, that two things are the same (or equivalent). ... This article does not cite any references or sources. ... In mathematics, an n-ary relation (or often simply relation) is a generalization of binary relations such as = and < which occur in statements such as 5 < 6 or 2 + 2 = 4. It is the fundamental notion in the relational model for databases. ... For other uses, see Reality (disambiguation). ... Nikola Tesla (1856-1943)[1] was a world-renowned Serbian inventor, physicist, mechanical engineer and electrical engineer. ...

External links

  • Lessons In Electric Circuits - Volume VI - Experiments
  • [1] Trochim, William M. Experimental Design. The Research Methods Knowledge Base, 2nd Edition. (version current as of July 11, 2006).
  • Description of weird experiments (with film clips)


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