Which question is not an example involving marginal analysis?

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.        

the question deals with financial planning and the answer is that dan did not stay on budget due to the fact that this guy needs to start decreasing his discretionary spending. according to the financial plan, he needed to balance his expenses and resources.