Randomized Block Design Rationale
The core challenge is to manage a variable that is strongly related (highly correlated) both to the independent variable (IV) and the dependent variable (DV). The goal is to ensure this correlated variable doesn't disproportionately influence the results across different levels of the IV.
Controlling Correlated Variables
The experimental design that best addresses this is the Randomized Block design. Here's why:
- Blocking Mechanism: Subjects are first grouped (or "blocked") based on the variable that is highly correlated with the dependent variable. For example, if age is highly correlated with the outcome, participants might be grouped into age blocks (e.g., 20-30, 31-40, etc.).
- Equal Representation: By forming these blocks, the experimenter ensures that each block (representing a specific level of the correlated variable) contains all the treatment conditions (levels of the independent variable).
- Reduced Error: Random assignment of treatments occurs *within* each block. This procedure isolates the variability due to the blocking variable, allowing for a clearer assessment of the IV's effect on the DV. It effectively controls for the influence of the extraneous correlated variable.
Evaluating Other Designs
Other designs are less suitable for this specific requirement:
- Repeated Measures: Involves using the same participants for multiple conditions, which doesn't inherently control for a pre-existing correlated variable between conditions.
- Randomized Groups: While random assignment helps distribute potential confounding variables, it doesn't specifically guarantee equal representation or control for a *known highly correlated* variable as effectively as blocking.
- Latin Square: Primarily used to control for two extraneous variables simultaneously (e.g., rows and columns), not typically the first choice for controlling a single, known correlated variable across IV levels.
Therefore, the Randomized Block design is the appropriate choice when an experimenter needs to ensure equal representation and control for a highly correlated variable.
Important Questions from Research Design
Design used in experimental research in which groups are randomly formed and that controls most sources of invalidity is known as
‘Which of the following are the complete experimental research designs?
(A) Factorial design
(B) One group after-only design
(C) Before-after design with one experiment and two control groups
(D) Latin square design
(E) One-group before-after design
Choose the correct answer from the options given below:
The 'Age' of a respondent is an example of
The internal validity factor in research is related to the issue of
The post-test only control group design avoids:
