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96 Disadvantages of Quasi-Experimental Designs One of the disadvantages of the quasi-experimental designs is that they lack random assignment of research participants to the two groups. That is, participants are not randomly assigned to the groups. In this regard, quasi-experimental designs are weaker than experimental designs in establishing causality since they use non-equivalent groups (comparisons groups) rather than control (equivalent) groups (Kettner, et al ., 2016; Marlow, 2011; Morra-Imas & Rist, 2009; Rubin & Babbie, 2013). Random assignment of participants takes into consideration different characteristics of the population, and thus it is representative of the population. So without randomisation, quasi-experimental designs have more threats to internal validity than pure experimental designs as it is not easy to account or control for extraneous and confounding variables. This may make it difficult for the researcher to establish causal relationships. For example, academic performance of children in a test score may be influenced by factors such as self- concept, socio-economic status, age, gender, and extra study hours, rather than intelligence which the experimenter may want to measure. Types of Quasi Experimental designs 1. Time Series Evaluation Designs Time series evaluation designs allow evaluators to make multiple observations of the group before and after an intervention is introduced. These designs permit researchers to observe changes in a group several times before and after the intervention and analyse trends before and after. Thus, time series designs use many pre-tests and post-tests as they measure changes in the group several times before the intervention and multiple times after the intervention. For example, girls may be tested on their knowledge of contraceptives several times prior to the training programme (Traeen, 2003). Focus Box 8: Quasi Experimental Design Evaluation An evaluation was done by Koeber (2005) on the use of multimedia presentations, particularly, ‘Power point’ and a course website named Blackboard. The two were being used in the teaching of introductory Sociology at a US university. The students were divided into two groups, the experimental and the comparison group without randomisation. Those in the experimental group were exposed to the two aforementioned forms of presenting learning material concurrently, while the comparison group were not. The findings revealed that there was no significant difference in performance (after observing their final grades) between those in the experimental and those in the comparison group. Nevertheless, students who were taught using the two aforementioned methods perceived the course in a more positive way than those in the comparison group. They also tended to view the workload as being light, than their counterparts