Final answer:
An example of a study with no confounded variable is a randomized controlled trial (RCT) where participants are randomly assigned to either a control group or an experimental group. An example of a study with a confounded variable is an observational study where the researcher does not have control over the assignment of participants to groups.
Step-by-step explanation:
An example of a study with no confounded variable for internal validity is a randomized controlled trial (RCT) where participants are randomly assigned to either a control group or an experimental group.
For example, in a study testing the effectiveness of a new drug, participants may be randomly assigned to receive either the drug or a placebo.
This way, the only difference between the groups is the presence or absence of the drug, eliminating confounding variables.
An example of a study with a confounded variable for internal validity is an observational study where the researcher does not have control over the assignment of participants to groups.
For example, a study examining the relationship between coffee consumption and heart disease may find a correlation between the two, but it is confounded by other variables such as smoking or diet.
The researcher cannot conclusively determine if it is the coffee itself or these other variables that are causing the observed relationship.