Payback time-frame for research in software engineering

What are the major questions in software engineering that researchers should be trying to answer?

A high level question whose answer is likely to involve life, the universe, and everything is: What is the most cost-effective way to build software systems?

Viewing software engineering research as an attempt to find the answer to a big question mirrors physicists quest for a Grand Unified Theory of how the Universe works.

Physicists have the luxury of studying the Universe at their own convenience, the Universe does not need their input to do a better job.

Software engineering is not like physics. Once a software system has been built, the resources have been invested, and there is no reason to recreate it using a more cost-effective approach (the zero cost of software duplication means that manufacturing cost is the cost of the first version).

Designing and researching new ways of building software systems may be great fun, but the time and money needed to run the realistic experiments needed to evaluate their effectiveness is such that they are unlikely to be run. Searching for more cost-effective software development techniques by paying to run the realistic experiments needed to evaluate them, and waiting for the results to become available, is going to be expensive and time-consuming. A theory is proposed, experiments are run, results are analysed; rinse and repeat until a good-enough cost-effective technique is found. One iteration will take many years, and this iterative process is likely to take many decades.

Very many software systems are being built and maintained, and each of these is an experiment. Data from these ‘experiments’ provides a cost-effective approach to improving existing software engineering practices by studying the existing practices to figure out how they work (or don’t work).

Given the volume of ongoing software development, most of the payback from any research investment is likely to occur in the near future, not decades from now; the evidence shows that source code has a short and lonely existence. Investing for a payback that might occur 30-years from now makes no sense; researchers I talk to often use this time-frame when I ask them about the benefits of their research, i.e., just before they are about to retire. Investing in software engineering research only makes economic sense when it is focused on questions that are expected to start providing payback in, say, 3-5 years.

Who is going to base their research on existing industry practices?

Researching existing practices often involves dealing with people issues, and many researchers in computing departments are not that interested in the people side of software engineering, or rather they are more interested in the computer side.

Algorithm oriented is how I would describe researchers who claim to be studying software engineering. I am frequently told about the potential for huge benefits from the discovery of more efficient algorithms. For many applications, algorithms are now commodities, i.e., they are good enough. Those with a career commitment to studying algorithms have a blinkered view of the likely benefits of their work (most of those I have seen are doing studying incremental improvements, and are very unlikely to make a major break through).

The number of researchers studying what professional developers do, with an aim to improving it, is very small (I am excluding the growing number of fake researchers doing surveys). While I hope there will be a significant growth in numbers, I’m not holding my breadth (at least in the short term; as for the long term, Planck’s experience with quantum mechanics was: “Science advances one funeral at a time”).

How much is a 1-hour investment today worth a year from now?

Today, I am thinking of investing 1-hour of effort adding more comments to my code; how much time must this investment save me X-months from now, for today’s 1-hour investment to be worthwhile?

Obviously, I must save at least 1-hour. But, the purpose of making an investment is to receive a greater amount at a later time; ‘paying’ 1-hour to get back 1-hour is a poor investment (unless I have nothing else to do today, and I’m likely to be busy in the coming months).

The usual economic’s based answer is based on compound interest, the technique your bank uses to calculate how much you owe them (or perhaps they owe you), i.e., the expected future value grows exponentially at some interest rate.

Psychologists were surprised to find that people don’t estimate future value the way economists do. Hyperbolic discounting provides a good match to the data from experiments that asked subjects to value future payoffs. The form of the equation used by economists is: e^{-kD}, while hyperbolic discounting has the form 1/{1+kD}, where: k is a constant, and D the period of time.

The simple economic approach does not explicitly include the risk that one of the parties involved may cease to exist. Including risk is non-trivial, banks handle the risk that you might disappear by asking for collateral, or adding something to the interest rate charged.

The fact that humans, and some other animals, have been found to use hyperbolic discounting suggests that evolution has found this approach, to discounting time, increases the likelihood of genes being passed on to the next generation. A bird in the hand is worth two in the bush.

How do software developers discount investment in software engineering projects?

The paper Temporal Discounting in Technical Debt: How do Software Practitioners Discount the Future? describes a study that specifies a decision that has to be made and two options, as follows:

“You are managing an N-years project. You are ahead of schedule in the current iteration. You have to decide between two options on how to spend our upcoming week. Fill in the blank to indicate the least amount of time that would make you prefer Option 2 over Option 1.

  • Option 1: Implement a feature that is in the project backlog, scheduled for the next iteration. (five person days of effort).
  • Option 2: Integrate a new library (five person days effort) that adds no new functionality but has a 60% chance of saving you person days of effort over the duration of the project (with a 40% chance that the library will not result in those savings).

Subjects are then asked six questions, each having the following form (for various time frames):

“For a project time frame of 1 year, what is the smallest number of days that would make you prefer Option 2? ___”

The experiment is run twice, using professional developers from two companies, C1 and C2 (23 and 10 subjects, respectively), and the data is available for download :-)

The following plot shows normalised values given by some of the subjects from company C1, for the various time periods used (y-axis shows PresentValue/FutureValue). On a log scale, values estimated using the economists exponential approach would form a straight line (e.g., close to the first five points of subject M, bottom right), and values estimated using the hyperbolic approach would have the concave form seen for subject C (top middle) (code+data).

Normalised returned required for various elapsed years.

Subject B is asking for less, not more, over a longer time period (several other subjects have the same pattern of response). Why did Subject E (and most of subject G’s responses) not vary with time? Perhaps they were tired and were not willing to think hard about the problem, or perhaps they did not think the answer made much difference. The subjects from company C2 showed a greater amount of variety. Company C1 had some involvement with financial applications, while company C2 was involved in simulations. Did this domain knowledge spill over into company C1’s developers being more likely to give roughly consistent answers?

The experiment was run online, rather than an experimenter being in the room with subjects. It is possible that subjects would have invested more effort if a more formal setting, with an experimenter who had made the effort to be present. Also, if an experimenter had been present, it would have been possible to ask question to clarify any issues.

Both exponential and hyperbolic equations can be fitted to the data, but given the diversity of answers, it is difficult to put any weight in either regression model. Some subjects clearly gave responses fitting a hyperbolic equation, while others gave responses fitted approximately well by either approach, and other subjects used. It was possible to fit the combined data from all of company C1 subjects to a single hyperbolic equation model (the most significant between subject variation was the value of the intercept); no such luck with the data from company C2.

I’m very please to see there has been a replication of this study, but the current version of the paper is a jumble of ideas, and is thin on experimental procedure. I’m sure it will improve.

What do we learn from this study? Perhaps that developers need to learn something about calculating expected future payoffs.