Links for Students

To anyone else who will eventually be doing a PhD defense, here are a few useful links I've come across recently.

10 Ways to Successfully Defend Your PhD: This focuses on the presentation itself. There appear to be other useful articles on the website if you want to look around.

Hints from CS at Columbia: This is the link that helped me understand the point of the defense. Specifically, getting everyone on the same page in case some of your committee did not read every section so that if one person asks a specific question, everyone will understand the context when you answer.

Preparation tips for Rochester University: This link talked about the basic logistics. If you are a PhD student and haven't attended a defense yet, make it a priority long before your turn. There are also always snacks.

Prepare your PhD Defense Presentation: This one did a nice job of demonstrating what a research question is.

Good luck!

Edit: Just found a super helpful Defense Outline.

Don't ask "which one is right?"

The above quote came from this blog post discussing the PACE trial which was a large-scale randomized controlled study comparing different treatment approaches for Chronic Fatigue Syndrome. I would not necessarily recommend reading the post since it can be hard to follow, and the comments suggest that in fact the study actually only provided evidence that the placebo effect holds...

But separate from all that, people tend to be uncomfortable with uncertainty. The setup of the study was supposedly to demonstrate which of different treatment options were effective. However, different people are likely to have varying responses to the same treatment. For something like CFS, it then makes sense to start your study with a question like "how can we identify the right treatment for each person" rather than "which treatment is right for everyone."

These questions come up a lot in the relatively new field of personalized medicine. While doctors have always used patient-specific information to make healthcare decisions, policy makers typically have not. Sometimes that makes sense: Eating more plants and getting more exercise are good for pretty much everyone. But we should not let our desire to have one right answer get in the way of understanding complex systems.

The Greenfield Bridge in Pittsburgh

A speaker in my department reminded us about the bridge-under-the-bridge in Pittsburgh, which involved building a bridge to catch falling debris from traffic-carrying bridge above. The speaker posited that perhaps the resources that went into building the second bridge would have been better spent fixing the broken bridge.

The bridge is finally being replaced (link here). The article actually provides numbers we can use to decide if, in hindsight, the secondary bridge was a good idea.

The bridge is projected to cost 19 million dollars in today's dollars to build, while the secondary bridge cost $625,000 in 2003 dollars. Based on the CPI, $1 in 2003 would be $1.29 today, and therefore the bridge would cost about $800,000 in 2015 dollars. But it turns out that is pretty irrelevant since $800,000 / $19 million = 4.2%. Assuming building new bridges wasn't wildly cheaper back in 2003, this was an obviously good investment since the bridge lasted 12 years, not one.

I will add one caveat: I don't know a lot about how these kinds of capital projects are funded. The replacement bridge project page mentions that 5% of the funding is coming from the city, 15% from the state, and 80% from the federal government. The above analysis in some ways assumes that the breakdown is the same for the secondary bridge. However, it appears likely that the city of Pittsburgh covered the full cost of the under-bridge. That puts their investment in 2003 for the past 12 years of bridge as about the same as for an entirely new bridge which will hopefully last 100 years. From that perspective, the city's best decision is a little less clear.

Salt, plow, or do nothing?

Last week we had a reminder of what an inch of snow can do at the wrong time. But how should a city decide when and how to act to avoid unsafe roads?

Modeling what will happen is tricky. The Washington Post link mentions that they get information from the "High-Resolution Rapid Refresh" weather model, which they say typically does well for short-term storms. They also cited a concern by city officials that low temperatures would result in the brine application freezing instead of keeping the roads ice-free. This means that the physics-side of the problem is tricky to figure out.

In addition to predicting what different snow-removal solutions would do, cost plays a role. Salting in some ways is preferable since it can be done ahead of the storm, but it depends on an accurate estimate of not-too-much snow falling. Plowing on the other hand requires you to wait until snow has actually built up, but then you know with certainty how much snow there is (taken to the extreme, the city of Ann Arbor does nothing until it stops snowing).

There do not seem to be comprehensive models which do the optimal tradeoff between the cost of accidents and lost productivity and the cost of snow removal. One could argue that a policy like Ann Arbor's makes the most sense since discouraging drivers in bad weather limits the number of accidents. But that only works if people are able to stay home, which is only sometimes true. If snow falls after people have already driven to work (which is frequently the case for these public failures), doing something so they can get home safely becomes much more important.

Are you a change agent?

Last fall I attended a Lean Green Belt certification course put on by IIE. One of the things that it included was this partitioning of people:

• 20% of people who are change agents.
• 60% of people who get on board once they see results.
• 20% of people who don't want to change.

While the exact percentages are obviously made up, the strategy they mentioned based on this partitioning is still useful. You start by getting a group of people together who are excited for positive change. By your combined forces you get some initial results which you can use to convince the middle people. Finally, simply outrun the people who are unwilling to change.

I was talking this idea over with a friend, and we joked about making a survey which asked people to classify themselves. It was a fun idea, but highlights one way new projects get derailed. In a study, 82% of adults say they have done something in the past six months to contribute to positive social change. In an optimistic world where the number is accurate, that matches up nicely with the made-up percentages above if you assume the middle people find something with evidence behind it to pursue. But it still makes it harder to figure out who to include in your initial concept-motivated group, and who to bring on board after you have some success.

Think about the incentives.

When you start applying game theory to business, the first question to ask is "what are everyone's incentives?" For example, when you buy insurance, you are trying to limit your risk in the event of a low-probability but very high cost event. An insurance provider on the other hand is interested in making as much profit as possible. They accomplish their goal by increasing total premium payments (rate * customers) while limiting how much they pay back out.

When incentives are misaligned, things that "don't make sense" from your point of view happen more frequently. If you have a car accident, from your perspective this is exactly why you bought insurance. From the insurance companies perspective, they would like to keep you as a customer in the future if the cost of fixing this accident is low enough¹. If the cost is higher though... they'd rather make it as difficult as possible for you to get a pay out.

My recent experience with this was that I rented a car from a company I won't name here. Most of the experience went well, which seems to be hard to come by for rental car companies. Except, I forgot my GPS in the car. Since it is clear that the GPS would have been found on cleaning the car, I reported a lost item, and the value of a GPS is pretty low by comparison to any future rentals, you might expect that it would have been returned. However, their are four players in this situation. Me, the car rental company, the specific rental location, and the person actually cleaning the car. It clearly benefits me to get my GPS back. It benefits the car company if I choose to use them again. It benefits the specific rental location considerably less than HQ in expectation. And it benefits the person cleaning the car to have a bonus GPS unless there are negative repercussions to them.

In short, a new GPS is purchased and on the way to me. I don't plan on using this rental company again, but I much more strongly don't plan to forget things in the car next time.

---

1 The benefit of you staying a customer also includes any word-of-mouth generated by how the incident is handled.^↩

Dutch Flower Auctions

If you have ever learned about auctions in a class, you will have heard about both "English" and "Dutch" auctions. The idea of an English auction is that you start at a low price and the bids keep increasing until the highest bid wins. The Dutch auction on the other hand starts at a high price which keeps dropping until one of the bidders says they are willing to pay the current price.

When you first hear about this auction, it is not clear why anyone would prefer the "Dutch" descending price auction, even if it officially gets the same expected revenue to the seller. But after finally seeing a video of how these auctions are run, it makes a lot more sense to me. My intuitive understanding now is that if you want to run a lot of auctions quickly, this is somehow simpler than it would be to run the auctions in an ascending-price way. (Something this video misses is that after the buyer wins, they submit how many flowers they want and the remainder get re-clocked. So that's why the clock keeps re-starting around 20 cents)

One closing thought: This NYT story suggests that the days of the clock auction may be numbered as buyers get larger and more of the time work directly with the sellers. I wonder what textbook authors will use to talk about the revenue-equivalence theorem then...