Image by Maia Weinstock.

Why do you want to be a scientist?

Casey Greene
5 min readOct 19, 2014


What to write in a compelling personal statement for Ph.D. programs in the sciences.

Life as a scientist

One of the things I love most about my job as a scientist is that I spend my time expanding the bounds of human knowledge. This means that in my lab we’re looking at aspects of biology that haven’t been explored before. In biomedical research we try to better understand the world around us in the hope that this understanding will improve our ability keep people well or make them well again.

Because research is focused on the unknown, the process can be frustrating. We construct a model of what we think truth to be, but often we will perform an experiment that indicates that our model is incorrect. We then construct a new model and identify a way to test aspects of that model. It may take weeks to construct another model that explains existing data; more weeks to figure out how to test that model; and only hours to find out that that model is also inadequate.

During research in most graduate programs, you will have a primary mentor but part of earning your Ph.D. is that you are becoming the true worldwide expert on your project. This means that your advisor will provide guidance, but this advice is often more general than specific simply because at some point during your research, you will understand the specific project that you’re working on better than your advisor will.

What this means for your personal statement

Given that this is what a Ph.D. program entails, I like to see at least three main things in a personal statement. If you have research experience, it’s very helpful to work that in to these elements where it applies. The statement should be concise (1–2 pages), because the admissions committee will be reading a lot of these.

1) Your mission: Given the challenges of this process, the students that I see succeed have the ability to focus strongly on an overall personal mission. For example, an overall personal goal that a student could have would be to “develop a cure for the cancers that are currently the most difficult to treat.”
Students should state their personal mission clearly, and the mission essentially answers the question: “What will compel you to come into work excited to pursue the problem you're working on, when you have already spent the previous month reformulating a model and the previous day you discovered that that model also does not explain some new data?”
This mission can be very general or very specific. You may change your mission as you learn more. No matter the case, this must be something that drives you in the pursuit of knowledge, and the most interesting personal statements also address why you chose this goal.

2) Your curiosity: Students need the curiosity to identify interesting and unexpected results and to pursue these discoveries if they relate to the overall goal. If I did X and observed Y, I should next do Z, but it could also mean that this other somewhat related research question about A may indicate B. Should I look into B by also testing hypothesis C through procedure D? Often unexpected results can be particularly illuminating, but there is a balance between what provides fruitful ground for follow up. Your advisor can help you decide whether potential experiments are worth your time, but the research endeavor works best if students are curious enough to identify the opportunity in the first place.
To demonstrate this curiosity, it helps to provide an example of a specific research question that you would be excited pursue. How does it fit into your overall goal and why would you be driven pursue it? An important aspect that is often left out: “What is currently known about the topic, and what gaps in knowledge would you like to fill in?” This shows that not only has your curiosity led you to this question, but also that you’ve cared enough about it to build on your understanding from existing scientific literature.

3) Your grit: Finally students need grit to push through the process. Much of the work that we do on a daily basis is frustrating. If I judged my job per day, I have many more days where I work toward a goal without getting an answer than I do exhilarating days where I've learned something totally new. That said, the excitement that results from discovering the undiscovered is wonderful. Realizing that it may one day improve the lives of other people is even better. As a scientist there are really amazing days, but because there are a lot more low days than high days, this aspect can be the most challenging part of graduate school.
When you’re writing your personal statement, consider which experiences in your life have demonstrated your grit? When you got knocked down, what got you up again? Your statement should demonstrate that you understand that this process is going to be difficult. Some things will work, and many things won't. What about your experience has given you the ability to push through on the hardest days?

Because research is fundamentally about examining the unknown, sometimes you will be right more often, and things will proceed very quickly. Sometimes you will be wrong more often, and things will proceed very slowly. Because of this, it's impossible to say how long a Ph.D. program will last, but as students proceed they constantly develop better intuition for such things. A project that seems straightforward may not be, and one that seems convoluted may actually go quickly. I love my job as a scientist but it’s not for everyone.

If you think science is for you, best of luck on your applications!

Casey Greene is a professor of Systems Pharmacology in the Perelman School of Medicine at the University of Pennsylvania and a Moore Investigator in Data-Driven Discovery. He occasionally tweets as @GreeneScientist. His lab accepts Ph.D. students from the GCB and CAMB/GGR graduate programs at Penn. Additional information is available on the lab website.



Casey Greene

Assistant Professor of Systems Pharmacology at @PennMedicine.