Problem: In experimental research design, one or more independent variables are manipulated by the researcher, subjects are randomly assigned to different treatment levels), and the results of the treatments on outcomes are observed. The unique strength of experimental research is its internal validity (causality) due to its ability to link cause and effect through treatment manipulation while controlling for the false effect of extraneous variables (Pelz, 2018). The example you have provided is great that in experimental research experimental group will be used to see the effect of the experiment. Quasi-experimental resembles experimental research but is not true experimental research. The difference is there is no control group and samples are not assigned randomly although the independent variables are manipulated. In your example of quasi-experimental research, participants will be observed for the effect of wearing tracker before and after and can be used for comparison but no control group is used.