Name: random assignment in experiments
Uploaded: 2023-04-30T12:27:36.000Z
Duration: 1 min 12 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Chemistry

CH.1

CH.1.c

What is an Experiment?

An experiment is a systematic approach to prove or disprove a hypothesis and uncover new knowledge. Statistics is often used to interpret the results of an experiment.
Consider an experiment to determine the relationship between mobile phone usage and sleep quality among college students.
These students, referred to as subjects, are divided into two groups. One is experimental, while the other is a control group. Only the experimental group is allowed to use mobile phones thirty minutes before bedtime, while the control group acts as the standard of comparison.
Researchers then record the number of hours of sleep and sleep latency or variables - the characteristics of subjects that are examined, measured, and interpreted.
Variables are of two types: dependent and independent.
Mobile phone usage is an independent variable controlled by researchers, and sleep hours and sleep latency are dependent variables that are measured and recorded.
Finally, hypothesis testing is used to infer whether the observed changes in sleep quality in the experimental group over the control group are statistically significant.

wat is een experiment?

Een experiment is een vooraf geplande onderzoeksactiviteit die wordt uitgevoerd onder gecontroleerde omstandigheden. Het doel van een experiment is om de relatie tussen twee variabelen te analyseren. Wanneer een variabele een verandering in een andere veroorzaakt, noemen we de eerste variabele de verklarende variabele of onafhankelijke variabele. De variabele die hierdoor beïnvloed wordt, noemen we de responsvariabele of afhankelijke variabele.

In een gerandomiseerd experiment manipuleert de onderzoeker de waarden van de verklarende variabele en meet vervolgens de resulterende veranderingen in de responsvariabele. De verschillende waarden van de verklarende variabele worden behandelingen genoemd. Een experimentele eenheid is een individueel object of subject waarop metingen worden uitgevoerd.

Stel dat je de effectiviteit van vitamine E bij het voorkomen van ziekten wilt onderzoeken. Je selecteert een groep proefpersonen en vraagt hen of ze regelmatig vitamine E innemen. Je constateert dat de proefpersonen die vitamine E gebruiken gemiddeld een betere gezondheid hebben dan degenen die dit niet doen. Bewijst dit dat vitamine E effectief is bij ziektepreventie? Nee. Er zijn veel andere verschillen tussen de twee vergeleken groepen naast de consumptie van vitamine E. Mensen die regelmatig vitamine E innemen, nemen vaak ook andere maatregelen om hun gezondheid te verbeteren, zoals regelmatige lichaamsbeweging, een gebalanceerd dieet, andere voedingssupplementen en het vermijden van roken. Elk van deze factoren kan invloed hebben op de gezondheid. Zoals beschreven, bewijst dit onderzoek niet dat vitamine E de sleutel is tot ziektepreventie.

Bijkomende variabelen die een onderzoek kunnen verstoren, worden verstorende variabelen of lurking variabelen genoemd. Om te kunnen aantonen dat de verklarende variabele daadwerkelijk een verandering in de responsvariabele veroorzaakt, moet de verklarende variabele worden geïsoleerd. De onderzoeker moet het experiment zo ontwerpen dat er slechts één systematisch verschil bestaat tussen de vergeleken groepen: de geplande behandelingen. Dit wordt bereikt door willekeurige toewijzing van experimentele eenheden aan behandelingsgroepen.

Wanneer proefpersonen willekeurig aan een behandeling worden toegewezen, worden alle mogelijke verstorende variabelen evenredig over de groepen verdeeld. Op dat moment is het enige systematische verschil tussen de groepen de interventie die door de onderzoeker wordt opgelegd. Daarom moeten de verschillende gemeten uitkomsten in de responsvariabele een direct gevolg zijn van de toegepaste behandelingen. Op deze manier kan een experiment een causaal verband aantonen tussen de verklarende en de responsvariabele.

Deze tekst is een bewerking van <a href="https://openstax.org/books/introductory-statistics/pages/1-4-experimental-design-and-ethics">Openstax, Inleidende statistieken, sectie 1.4 Experimenteel ontwerp en ethiek</a>

Wat is een experiment?

An experiment is a planned activity carried out under controlled conditions. The purpose of an experiment is to investigate the relationship between two ...

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random assignment in experiments

Random assignment in experiments helps researchers test cause and effect between two variables. An experiment is a planned activity carried out under controlled conditions. It is used to study how one variable affects another. The variable that causes change is the explanatory or independent variable. The variable that changes in response is the response or dependent variable.

In a randomized experiment, the researcher changes the explanatory variable and measures the response variable. The different values of the explanatory variable are called treatments. An experimental unit is the single object or individual that is measured. This structure lets the researcher compare treatment groups under the same planned conditions.

A simple health example shows why random assignment matters. Suppose a researcher wants to test whether vitamin E helps prevent disease. If people are only asked whether they already take vitamin E, the group that takes vitamin E may look healthier on average. But that result does not prove vitamin E is the reason.

Other differences can affect the outcome. People who take vitamin E regularly may also exercise more, eat better, take other vitamin supplements, or choose not to smoke. These extra influences are called lurking variables. They can cloud a study and make it hard to tell which factor is really causing the change.

To isolate the explanatory variable, the researcher must design the experiment so that the treatment is the only planned difference between the groups. This is done by random assignment of experimental units to treatment groups. Random assignment spreads potential lurking variables more equally among the groups. Then differences in the response variable can be linked to the treatments themselves.

Random Assignment in Experiments

what is an experiment?

Random assignment in experiments helps researchers test cause and effect between two variables. An experiment is a planned activity carried out under controlled conditions. It is used to study how one variable affects another. The variable that causes change is the explanatory or independent variable. The variable that changes in response is the response or dependent variable. In a randomized experiment, the researcher changes the explanatory variable and measures the response variable. The...

study design in statistics

Experimental and Observational Study Types

Study design in statistics helps researchers collect and analyze data from variables in a specific research problem. It supports stronger experiments and more reliable data. Questions about aspirin and heart attacks, fertilizer and rose growth, or fatigue and alcohol-related driving risk all depend on careful study design. Study designs are usually grouped into two main types: descriptive and analytical studies. Descriptive studies describe the variables and answer what is happening, rather...

observational studies

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Observational research methods let scientists study events without changing them. The researcher does not intervene, so the response variable and the outcome are left alone. These studies are used to look for patterns and relationships in real-world settings. There are three main types of observational studies: prospective, retrospective, and cross-sectional. Each type collects information in a different way. Together, they help researchers answer questions about health, behavior, and risk. <br...

experimental designs

Types of Experimental Design

Experimental design is a systematic way to study how an independent variable affects a dependent variable. Researchers use it to compare results and judge whether a treatment or intervention changes the outcome. Three common experimental designs are pre-experimental design, true experimental design, and quasi-experimental design. Each one supports research in a different way, depending on how groups are formed and how the data are collected. In pre-experimental design, the researcher compares...

randomized experiments

How Random Assignment Reduces Bias

Random assignment helps researchers place participants into experimental and control groups. It gives each person an equal chance of being assigned to either group. This process is used to reduce selection bias and to balance known and unknown confounding factors, so the control group is as similar to the treatment group as possible. A computer program or a random number generator can make the assignment process less biased. Simple randomization is the most direct method. It uses a single...

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Crossover experiments are a repeated-measurements study design used in science and medicine. In this design, the same experimental units receive all treatments during different time periods. That setup helps compare how each treatment performs within the same group. These studies are used in psychology, the pharmaceutical industry, agriculture, and medicine. They can work with smaller sample sizes because the samples act as their own controls. That makes crossover designs useful when...

controls in experiments

Why Control Groups Improve Experiment Results

Control groups help experiments produce more reliable results. They reduce bias and make it easier to measure the dependent variable. In an experiment, controls have the same features as the treatment groups but are not affected by the independent variable. Researchers sort data into control and experimental conditions to see the relationship between the independent and dependent variables. A randomized experiment includes a control group that receives an inactive treatment. The control group...

bias

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Bias is any tendency that keeps a question from being unprejudiced. In research, bias appears when one outcome or answer is favored over others during sampling or testing. It can happen at many stages, including study design, data collection, analysis, and publication. A common form is sampling bias. This happens when a sample is taken from a population and some members are less likely to be chosen than others. In a fair sample, each member of the population should have an equally likely...

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Placebos and Bias in Randomized Trials

Placebos and blinding are key tools in randomized control trials, or RCTs. They help researchers reduce bias, which can affect study results. In a blinded study, participants do not know which treatment they are receiving. A placebo is a dummy treatment that does not contain the active treatment. Researchers use a placebo in the control group to compare against the treatment group. This helps balance the effects of being in an experiment with the effects of the active treatment itself. A...

clinical trials

How Clinical Trials Test New Treatments

Clinical trials test new treatments in people to check safety and effectiveness. These experimental studies can look at drugs, diet methods, and medical devices. Researchers use statistics to turn collected data into reasonable and accurate conclusions, so they can make sound decisions when results are uncertain. Statistics also help medical researchers reduce error and bias. That matters because clinical trial data can be influenced by chance or by uneven study design. Careful analysis...

key terms and concepts

Learn how randomized experiments use treatments, experimental units, and random assignment to test cause and effect while reducing lurking variables.

Random Assignment in Experiments | JoVE K12

statistics

JoVE Core Statistics introduces the concepts and application of the collection, analysis, presentation, and interpretation of data to students. These animated lessons provide an understanding of statistics beneficial to students from a wide range of disciplines. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide

Random Assignment in Experiments

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