Experimental design is true experiment, where we try to know
the effect and causal relationship in the study. In this design we
assign our sample using random methods. There are atleast one
experimental group and one control group.
Quasi experimental design, is based on observational studies,
in this design we can manipulate the independent variable, but we
select our sample through non- randamized method. In this design we
don't eliminate the problem of confounding variables. This design
is more likely to conduct in field setting.
Example (experimental design)- study on the effect of any
vaccination on particular disease.
Example (quasi- experimental design)- study on the effect of
any psychotherapy on any particular disorder.