Completely Randomized Design in Experiments

Completely Randomized Design (CRD)

• CRD: A type of experimental design where experimental units are randomly assigned to different treatments or conditions.
• This approach minimizes bias, enabling generalization of results.
• Experimental units, like plants, animals, or subjects, are randomly assigned to different treatments or conditions.

Definition of Terms

Randomization

• Definition: The process of assigning experimental units to different treatments or conditions randomly.
• This practice minimizes the influence of confounding variables, ensuring results are due to the treatment effect, not other systematic biases.

Randomized Control Trial (RCT)

• Definition: A type of experimental design assigning participants randomly to either a treatment or control group.
• RCTs are considered the gold standard in experimental research because random assignment controls for confounding factors.

Experimental Unit

• Definition: The smallest unit of observation in an experiment.
• This receives the treatment or intervention (e.g., single plant in agriculture).

Treatment

• Definition: A specific intervention, condition, or procedure applied to experimental units.
• Can include a drug, educational program, or different manufacturing process.

Control Group

• Definition: A group of experimental units not receiving the treatment being tested, but rather a placebo, no treatment, or standard treatment.
• Used for comparison, determining the effect of the experimental treatment.

Random Effects

• Definition: Factors in a model assumed random, drawn from a probability distribution.
• These factors represent sources of variability not of primary interest but contribute to the overall variability in data (e.g., individual differences).

Block Design

• Definition: An experimental design grouping experimental units into similar blocks.
• Treatments are randomly assigned within each block. This helps control variability between blocks, making the experiment more precise.

Replication

• Definition: Repeating an experimental condition or treatment within an experiment.
• Replication increases the reliability of results and allows for better estimation of variability.

Bias

• Definition: Systematic errors in design, data collection, or analysis leading to inaccurate or skewed results.
• Randomization helps reduce bias by ensuring treatments are assigned without bias.

Confounding Variables

• Definition: Variables related to both the treatment and the outcome, potentially distorting the observed relationship between them.
• Randomization helps minimize confounding by evenly distributing confounding variables across treatment groups.

Statistical Significance

• Definition: A statistical measure determining if observed effects in an experiment are due to chance or reflect a true relationship.
• Randomization increases the likelihood that statistical tests assess the significance of treatment effects correctly.

Stratified Random Sampling

• Definition: A sampling method dividing a population into subgroups (strata) based on characteristics.
• Random samples are drawn from each stratum. This ensures relevant subgroups are represented in the sample.

Control of Variables

• Definition: Keeping all variables constant except the independent variable being tested.
• Randomization helps control potentially confounding variables.

Random Assignment

• Definition: Assigning subjects or experimental units to different treatments randomly (using a random number generator).
• Ensures each subject or unit has an equal chance of being assigned to any group.

Sample Size

• Definition: The number of experimental units or subjects in an experiment.
• A larger sample size improves the precision of estimates and statistical tests' power.

Sampling Error

• Definition: The difference between a sample estimate and the true population value.
• Random sampling reduces sampling error by ensuring the sample represents the population.

Double-Blind Experiment

• Definition: An experimental design where neither participants nor experimenters know which treatment participants are receiving.
• This prevents bias in treatment administration and outcome measurement.

Placebo Effect

• Definition: A psychological phenomenon in which participants experience improvements simply because they believe they're receiving treatment.
• A placebo group measures this effect.

Factorial Design

• Definition: An experimental design testing multiple factors (independent variables) simultaneously to examine their individual and interactive effects on an outcome.
• Random assignment is often used to reduce bias.

True Experimental Design

• Definition: An experimental design using random assignment to treatment groups and controlled conditions to determine cause-and-effect relationships.
• Contrasts with quasi-experimental designs, lacking randomization.