Final answer:
Quasi-experimental research always involves the manipulation of independent variables, but it does not require random assignment of participants, which differentiates it from true experiments.
Step-by-step explanation:
Which is always a feature of quasi-experimental research? The answer is c) Manipulation of independent variables. Quasi-experimental research designs do not use random assignment of participants, unlike true experiments. However, they involve the manipulation of independent variables to observe their effect on dependent variables, even if the assignment to different conditions or treatments is not randomized. Quasi-experiments often use control groups and may employ pretests and posttests to measure the effects of the treatment.
Random assignment is a cornerstone of experimental design, ensuring that groups are comparable at the start of the study. This is essential for determining whether the observed effects are due to the manipulation of the independent variable rather than preexisting differences between groups. Quasi-experimental research cannot fully eliminate the problem of lurking variables like a true experimental design can, which is why it's considered less rigorous.
A placebo is sometimes employed in experimental research to address participant expectations influencing outcomes. However, this is not a feature specific to quasi-experiments, but rather to well-controlled experiments. Thus, the key feature of quasi-experimental research is the intentional alteration or manipulation of independent variables, despite not being able to randomly assign participants to groups.