True Experimental Design: A true experimental design is one in which the researcher manipulates the Independent Variable (or variables) to observe its effect on some behavior or cognitive process (the dependent variable) while using random assignment of participants to groups in order to control external factors from influencing the results. Without both manipulation of the IV and random assignment of participants, you do not have a true experimental design and, as a result, can’t establish cause and effect.
Quasi-experiment design The design of a quasi-experiment relates to the setting up a particular type of an experiment or other study in which one has little or no control over the allocation of the treatments or other factors being studied. The key difference in this empirical approach is the lack of random assignment. Another unique element often involved in this experimentation method is use of time series analysis: interrupted and non-interrupted. Experiments designed in this manner are referred to as having quasi-experimental design.
Conclusion: (quasi-experimental designs are often chosen for field studies where the random assignment of experimental subjects is impractical, unethical, or impossible). Also, the lack of random assignment in the quasi-experimental design method may allow studies to be more feasible, but this also poses many challenges for the investigator in terms of internal validity.
This deficiency in randomization makes it harder to rule out confounding variables and introduces new threats to internal validity because randomization is absent, some knowledge about the data can be approximated, but conclusions of causal relationships are difficult to determine due to a variety of extraneous and confounding variables that exist in a social environment.
So the True Experimental Design is better as I concluded.

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