What is a common limitation in observational research?

In observational research, a prevalent limitation is bias due to the researcher's subjectivity. This occurs because researchers observe and interpret data based on their perspectives, beliefs, or expectations, which can inadvertently influence the results of the study. For instance, a researcher's interpretation of behavior, events, or responses may be colored by their own biases, leading to conclusions that may not accurately reflect reality. This subjectivity can introduce various types of bias, such as confirmation bias, where researchers may favor observations that support their hypothesis while overlooking those that contradict it.

The other options illustrate elements less characteristic of observational research. High control over independent variables is more typical of experimental research, where researchers manipulate one or more variables to observe the effect. Reliance solely on experimental data does not apply here, as observational studies do not use experiments for data collection. Lastly, interaction with participants is generally limited in observational studies, but it's not a defining limitation like inherent bias, which can significantly impact the validity of the findings.