Factors that influence the results of a study that the researcher did not, or could not, account for are known as

The answer to this question is Confounding variables
Confounding variables often created to the failure in control by the researchers that will eventually damage the validity of the research.
For example, if researchers are finding the correlation between tofu consumption and breast cancer, the gene that improve the chance of causing cancer could be considered as confounding variables.

Hamlet's fourth soliloquy is probably his most famous one - "to be or not to be."it is rather different from his previous soliloquies because now he is contemplating something that didn't come up before - suicide. he is thinking whether it is worth it to fight to find his father's murderer when in the end all of them are going to die, so why not die sooner than later. he is contemplating if he should go on fighting or just kill himself and end it all, which is why this soliloquy in particular is rather depressing, hesitant, and gives a deeper insight into hamlet's madness.