When the AAMC revamped the MCAT in April 2015, there was a lot of discussion and hype surrounding new subjects on the exam: biochemistry, sociology and psychology. While those new topics are important, the AAMC actually added another new topic to the exam that most students are unaware of: the design and implications of scientific experiments.
Questions that require students to identify pieces of an experiment or explain abnormal results have been a part of the MCAT for decades, but never before has this aspect of the sciences been so overtly tested and so important to a student’s score. The two new “scientific inquiry and reasoning skills” on the exam – “reasoning about the design and execution of research” and “data-based and statistical reasoning” – comprise between 35 and 40 questions on the new exam. How important does this make these new skills? There will be more points hinging on these skills on your exam than organic chemistry, sociology or physics.
New Skills Tested
These new skills will test your scientific analytical ability by determining if you can “do” scientific research. This includes demonstrating your understanding of important components of experimental procedure. This is a trait medical schools want in their students because modern medicine combines disciplines from across the natural, physical and social sciences to research and extend medical knowledge.
These questions could ask you to identify how scientists control complex biological variables to test their theories. They could ask you to think about the ways medical researchers take their measurements. These questions could ask you to spot flawed research logic or point out the limitations of the research methods employed by the scientists. You may also be asked to recognize factors that might confound the conclusions drawn from the experimental results. These are all skills you will use in abundance during your third and fourth year clinical rotations in medical school.
Example of an Experimental Design Question
Let’s look at an example so we can see what the AAMC actually means when they talk about testing experimental design:
Question: Researchers performed a series of experiments to test the transport rate of the Na+/K+ ATPase pump in nerve cells. Which of the following results would be least helpful to draw conclusions about pump activity?
A. A plot of intracellular [Na+] over the course of the experiment
B. A plot of ATP hydrolysis over the course of the experiment
C. A plot of ΔG of [Na+] transport over the course of the experiment
D. A plot of membrane potential over the course of the experiment
This question requires us to identify the least appropriate measurement/result to draw reliable conclusions about the goal of the experiment. The experiment was designed to test the activity of the Na+/K+ ATPase pump, which we should know for test day is an ion pump that hydrolyzes 1 ATP molecule in order to have the energy needed to export 3 Na+ ions from the cell and import 2 K+ ions into the cell. The most direct way to measure pump activity is to measure the changes in Na+/K+ ion concentration inside the cell (eliminate choice A). The movement of ions into/out of the cell will also directly affect the membrane potential of the cell (eliminate choice D). The pump activity is also tied directly to the rate of ATP consumption (eliminate choice B). This leaves us with choice C, which mentions measuring the free energy (ΔG) of the system during the experiment. The free energy of a system may be used to study its thermodynamic properties (e.g. stability, equilibrium concentrations, spontaneity) but it will not tell the researchers anything about the dynamic activity (i.e. transport rates) of the pump. Thus, choice C is the least useful measurement to use, and is the correct answer.
Understanding Analysis & Controls
These research questions will require a good mix of content and experimental analysis. In addition to proper measurements, research design involves looking for proper controls. Every experiment has to have proper controls if researchers want to detect if a treatment had any effect. A common control test in scientific research is the baseline measurement, against which future measurements can be compared. While this experimental consideration is not new for the MCAT, the degree to which it is being tested is.
We also need to be aware of the difference between positive and negative controls. A negative control is how we typically think of a “control group.” That is, a group that gets no treatment at all. Researchers need to see what happens when we don’t use the treatment or experimental effect. By contrast, a “positive” control is a group that does get a treatment, but not an experimental one. The positive control group gets a treatment that we already know works.
For example, researchers testing a new analgesic drug could use the effects of Tylenol as a positive control. Researchers need to do both positive and negative controls when doing biomedical research, especially when the research has a psychosocial component.
On the MCAT, test takers would be expected to look for some sort of discussion of these control groups in the passage. If the discussion is missing, then there’s a pretty serious flaw in the study.
How Do I Practice these Skills?
The only way to develop the comfort and expertise you need for test day is to practice, practice, practice!
You should start by going to the AAMC website and picking up a copy of the official exam practice that the AAMC offers. That includes the Official Guide the Sample Test, and the recently released Scored Practice Exam (released November 2015).
Most students find, however, that the limited resources offered by the AAMC are not enough. They want the opportunity to practice multiple full exams and full sections under timed conditions. To that end, students often find success with the packages of full length exams available at Next Step Test Prep.
Dr. Anthony Lafond is the National MCAT Content Director at Next Step Test Preparation, a company that specializes in 1-on-1 tutoring for the MCAT. Anthony has taught or tutored students for the MCAT for ten years and has scored a 42 on the test himself.