Monthly Archives: August 2011

Punk Rock OR Podcast #2: An interview with undergraduate student researchers

I decided to resume the Punk Rock Operations Research Podcast. This new podcast episode is an interview with two undergraduate student researchers, Amber and Richard, that I have been working with this summer.  Both Amber and Richard have been working on a research project that investigates the role of weather on emergency medical calls, mainly using statistical methodologies.  They both agreed to let me interview them about their summer research projects.

You can listen to the episode below or you can go to the podcast web page (where you can download to iTunes, etc.) and feed. I recommend subscribing to the feed or going directly to the Punk Rock OR Podcast iTunes page, but you can also find the podcast episodes on this blog by clicking on “Podcast” under “Categories” in the left column.

Podcast episodes will be a semi-regular thing (that’s all I can promise for now–being a professor is a full-time job).  I’ll post updates on the blog.  I have two more podcast episodes in the works that will be available within the next week.

Your comments and questions are always welcome! I would love to answer your questions on air.  Send your comments to (If you send me an email, you consent to letting me use and showcase it in the blog, podcast episode, etc.).


the nut butter taste-cost tradeoff

There are two kinds of people: people who eat peanut butter directly out of the jar at the people who do not. I am in the former group, and so are my kids (they ask for “peanut butter spoons”). I am not very discriminating–I’ll eat all kinds of nut butter directly from the jar. For the record, I generally eat nut butters on bread.

The quality and cost of nut butters vary. This past week, I tried sunflower seed butter for the first time. It inspired me to make a figure capturing the taste-cost tradeoff in various nut butters, which is displayed below.

My favorite nut butter is Trader Joe’s peanut butter made from unblanched peanuts.  I like my homemade peanut butter (see recipe below) and soy butter almost as much.  Natural peanut butter (made by various companies) are also pretty good and frugal. Cashew butter is fantastic but expensive. I like almond butter and sunflower seed butter, but I’m not in love with them.  I ended up with four types of nut butters that are tasty enough to justify buying them (see the figure below).

Recipe: When I make peanut butter, I follow the following recipe.  I put the peanuts from a 12 oz. can of peanuts and salt to taste in my KitchenAid food processor. I process the peanuts along with safflower oil as needed until I end up with peanut butter of the desired consistency. I also make cashew butter using this recipe, except that I replaced the peanuts with cashews (of course!).  Almond butter is not as easy to make at home.

What are your favorite nut butters?

The nut butter taste-cost tradeoff.

The nut butter taste-cost tradeoff. The dotted line separates the tasty, frugal nut butters (in orange) from the nut butters that are not tasty enough to warrant their cost (in brown).

buying a new washing machine part 2

Since posting my last blog entry on how I loosely used multi-objective decision analysis to guide my decision to purchase a new washing machine, I have been accused of giving “more thought to [my] washing machine purchase than Congress gave to [the] budget.” This blog post is certainly not going to disprove that claim.

My husband and I based our purchase on prices, quality, and functionality.  In this post, I will confess that our analysis was somewhat wrong.  I thought that I knew what a new washing machine would be like. This was a reasonable assumption, since after all, I’ve been using washing machines for years.

Once I started to use the new washing machine, it became clear that

  1. loads take longer to complete (sometimes much longer to get clothes clean).
  2. laundry is less wet when it comes out of the washing machine.

The combination of these two points means that my dryer is no longer the bottleneck, it’s the washer. It also takes away some of the benefits of drying laundry outside. Air drying used to be a huge time saver for me in the summer. Not so any more. This is a good thing, because with a baby at home and tenure looming, I have less energy and more laundry to do. I use my dryer more frequently this year.  I no longer schedule my laundry around the dryer time, which has the side benefit of giving me a little more flexibility. The longer wash cycles are a pain, but the “Tumble Fresh” option keeps the laundry smelling fresh if I let it sit in the washer for a long time.

My time spent doing laundry is determined by the washing machine and its capacity. The large capacity of our new washer helps me to avoid splitting some loads of laundry into two loads, which would be necessary at a smaller capacity. A larger capacity wouldn’t necessarily save me any loads, because all of my “full loads” fit into our new washer. This will certainly change when my kids get bigger and wear bigger clothes, and I may kick myself for not buying the biggest capacity available.

All of this suggests replacing my “capacity” criteria with a “throughput” criteria, where the throughput can be evaluated by considering the total time spent “doing” laundry per week based on the total number of loads:

Total time = (Number of loads) x max{Washing Time, Drying Time}

Then, the mid-level washer becomes the overwhelming favorite, even when performing a sensitivity analysis on the weight for throughput (see below). Although this improvement is a step in the right direction, I remain skeptical of its usefulness.  Would I have come up with a spreadsheet to justify buying a high-level washer had we bought the priciest washer? I’ll have to leave that one a mystery and get back to work.

MODA analysis of washing machine purchase (take 2)

Related posts:

buying a new washing machine, a quick multiobjective analysis

I have just about lost count of the things that have broke in my house since mid May. The biggest appliance failure was the washing machine. It’s hard to go without a washing machine with three youngsters in the house.

The bearings could have been replaced for about $500, but a ~12 year old washing machine has a limited lifespan. My husband and I decided to purchase a new washing machine. Luckily, we were shopping for the washing machine over the Memorial Day weekend, when just about every appliance store put their washing machines on sale.  I started by grilling the washing machine repair person about what machines he would recommend. This was extremely useful in narrowing down our choices. After spending a couple hours reviewing reviews and prices, we narrowed our choices down to four:

  1. repair our existing machine
  2. a low end washing machine
  3. a mid-level washing machine
  4. a high end washing machine

My husband and I listed our criteria:

  1. Washing machine capacity (three kids = lots of laundry)
  2. Price
  3. Features (both for doing laundry and making my life easier)

The capacity varied from 3.5 cubic feet to 4.3 cubic feet.

The price captures the purchase price and the chance of a $500 repair in the next five years.  The price of the existing machine captures the immediate $500 and the probability of having to replace the machine in the next five years (where it would be replaced b ya mid-level machine). Repairing the existing machine came out to be the most expensive option over the next five years. The costs varied from $451 -$1222. We didn’t consider operating cost, because the water and detergent costs were dwarfed by the purchase and repair costs.

The features is a constructed scale, which captures on a scale from 0 to 4 how useful I find the features. The low end washing machine didn’t offer anything about the bare minimum, whereas the high end washing machine just about does the laundry itself.  The mid-level and my existing washing machines offered nice features that I would take advantage of, and I scored them at 3 and 2, respectively.

After looking at the machines, I fell in love with the high end washer, despite its hefty price tag. My husband preferred the mid level washer. The high end washer has a larger capacity and features to keep laundry fresh when a wet load of laundry sits in the washer overnight. I eventually sided with my husband, since buying a high end washer would make him less inclined to buy me a fancy range/oven for my birthday. A fancy oven would help me bake the best possible Christmas cookies, so I don’t think I can live without it for much longer.

When researching the new washer, I did a quick multi-objective decision analysis on the washing machine decision with the three criteria mentioned earlier. I estimated our swing weights to be 0.25 for capacity, 0.60 for price, and 0.15 for features.

The values for the four options are:

  1. repair our existing machine   = 0.27
  2. a low end washing machine    = 0.60
  3. a mid-level washing machine = 0.61
  4. a high end washing machine   = 0.58

The highest value was for the washing machine my husband preferred, the washing machine that we ended up purchasing. Does that mean we made the right decision? Not so fast.  Three options have similar values.  The three machines have different capacities, and capacity is a proxy for my time (less capacity = more time doing laundry). A quick sensitivity analysis on the weight for capacity (illustrated below) suggests that if we weigh capacity slightly more heavily, we should have chosen the the high end washer, and if we weigh capacity slightly less heavily, we should have chosen the low end washer. This quick MODA analysis has only convinced me that any decision could have been OK, except keeping our washing machine.

MODA analysis of washing machine purchase

MODA analysis of washing machine purchase


land O links

Yikes! I meant to post this a month ago. Here are a few (dated) links:

a Darth Vader carrot

a Darth Vader carrot

are bloggers journalists?

Are bloggers journalists? Or more specifically, are blogging professors journalists?

I hadn’t given this question much thought until someone overheard me having a work conversation at Panera and thought I was an investigative journalist. (I wasn’t talking about journalism or even the news, I was explaining some mathematical modeling issues to a layperson).  My response to the journalist question was that I was a professor. Now I wonder if I should have described myself as a blogging professor.

I don’t think of myself as a journalist, even though a blog has the same ability to host new news stories as do newspapers. I realize that blogs mostly regurgitate news that has already been reported, but bloggers increasingly break new news stories. It’s great to be a part of that. I try to write about new news stories (e.g., posts about conferences) and stories that fall outside of regular journalism outlets (e.g., math models of zombies, vampire populations, and my morning cup of joe). Do bloggers deserve the same press protections as journalists? I suppose it depends on what kind of blogger you are. I hope I never need press protection.

A recent survey reports that 52% of bloggers consider themselves journalists. The number continues to grow because “it’s cool to be a journalist.” But it’s even cooler to be a professor of operations research. At least I think so. So I’ll continue to see myself as a professor who blogs, and I’ll consider blogging to be outreach and good nerdy fun rather than journalism.