Hi Julia! I'm just starting my PhD, and my supervisor gives me a lot of freedom and independence. While I appreciate that, I'm not sure where to start tackling my project. I've done a lot of reading, but I'm having trouble designing good experiments. Do you have any suggestions?
I have a post here outlining one possible path to take when designing your thesis projectâhowever, it does involve communicating with the PI almost every step of the way. I do think that PI involvement is pretty crucial for the development of a PhD student, so if thereâs a way for you to have weekly one-on-one meetings with your PI, I think youâll find that would be really beneficial.Â
In the meantime, letâs talk about experimental design. Itâs a very important skill we learn during grad school, and one of those skills that separates someone with a PhD and someone without. Itâs part of the âPhâ part of the degree, after all! So if youâre not getting the mentoring necessary to learn how to properly design experiments, then thatâs a huge foundation of your PhD thatâs missing. If your program (or any related programs) has a class on experimental design, it would be worth taking (I took two different experimental design courses, on top of regular guidance from my PI, and years later Iâm still learning so much about the nuances of experimental design). Regardless, as a minimum requirement for a PhD mentor, your PI should be teaching you proper experimental design and results interpretation. Otherwise theyâre just a warm money-pumping-lab-having body for the next 4+ years and thatâs not what you, a PhD student, are here for, or deserve.
However, I do understand the reality that is busy PIs and large labs. If your PI is really hard to get a hold of, you can try finding other mentors to help guide you, such as: other senior members in the lab (like the lab manager, research specialists, post-docs, even other grad students), your committee members, the PI next door even. I get advice from as many people as I can, because sometimes even if my PI is available, she may not have the best expertise in certain situations.Â
As a supplement, I would also recommend finding online resources on experimental design. A quick google search of âexperimental design in biologyâ lead me to this awesome video from Khan Academy that covers experimental design at its simplest.Â
Now hereâs a quick and dirty 4-step crash-course on experimental design (from my experience in doing biology research):
1) Start with a testable and feasible research question:
This is based off a hypothesis/prediction you make, which in turn is based off the knowledge gaps in your research area
It can be as simple (one experiment) or as complex (aka the focus of your entire dissertation) as you want it to be
It should be testable: you actually have a way to figure out the answer
And also feasible: given your time, ethics, and resources (eg. equipment available, funding, people who can help you)
This is something that reading the literature, or talking to your PI, can help with.Â
(Divide up your research question into sub-questions if necessary)
âYesâ and âNoâ research questions are totally ok. Sometimes itâs as simple as âdoes my cell line constitutively express this receptor, yes or no?â or âdoes Treatment X induce my cell to secrete Protein Z, yes or no?â
2) Come up with a method to answer the question:
I like to first go into âfantasyâ mode. Like, what would the perfect assay be to answer this? I pretend itâs the year 3050 and whatever I think of we can do. For example: âah if only i had xray vision and the ability to tell apart a human tumor cell from mouse bone marrow and can see just how many of these tumor cells end up in the bone with my naked eye!â Thinking like this first lets you get to the bottom of âwhat do we need to solve this problem?âÂ
Ok, time to go back to the present. We canât see tumor cells through bone with the naked eye, but what do we have that allows us to do so indirectly? How can I tell the difference between a human cell and a mouse cell, and also quantify that?Â
Another part of the design process where reading the literature and/or talking to your PI and other researchers would help with, especially if you donât know what you donât know.Â
Like if I have no idea that something like intracellular fluorescent labeling and flow cytometry existed to solve my question at hand, I couldnât even use that in my experiment
Determining the method you will use is sometimes the most time-consuming part imo. If itâs something you or the lab havenât done before, youâll need to do a lot of research into the methods (whatâs the best reagent? concentration of reagent? do we have access to equipment necessary? do i need specific controls? whatâs the specificity and sensitivity of this assay? are there background issues i have to contend with (eg. autofluorescence))? It may take a few tries with optimization before getting the method down for your purposes. And as you can see, it can be super involved, so getting advice and help from your PI or another expert would be really helpful (and time saving!)
3) Design the experiment on paper with the proper variables, controls, and replicates:
I like to pretend Iâm solving a murder mystery and I have to convince the jury that Suspect A, with weapon C, is the one who dun it. How do I go about designing an experiment that will eliminate all possible suspects and murder weapons (and thus convince the jury)?Â
Sometimes it helps to draw a predicted results graph of your experiment; seeing it in its âfinalâ form may help you realize some controls or treatment combos may be missing.Â
Once youâve designed the experiment, go over it with your PI (or another expert), to make sure itâs sound.
The number of replicates (technical vs biological) you may need will depend on statistical analyses, like power analyses and what kind of statistical experimental design (eg. one-tailed vs two-tailed) youâve decided beforehand. If this all sounds new, then thatâs something youâll need expert advice on (like from your PI), or take a class in (like biostats), or do lots and lots of independent research (perhaps the most time-consuming and mistake-prone choice). At a minimum though, we always need at least 3 values to perform any stats (so if youâre just running something up the flagpole, n=3 is a quick and dirty thing to do first).Â
4) Predict the outcomes of each of your variables and controls and do some thought exercises
Ask yourself if these predicted results will answer your question
If it only answers part of your question, what else do you need?
If it doesnât really answer your question, what should be changed?Â
What if the opposite of what you predicted happens? What would that mean?Â
If all this seems super overwhelming, then I think itâs a sign to seek out specific help on experimental design, like your PI or a class. Again, itâs part of your PhD training, but itâs not something you need to, or should, learn all by your lonesome self.Â
Good luck with your training and research! I hope you find a good path forward.Â