Why few women in engineering?

The Washington Post recently published an opinion piece by Catherine Rampell with a somewhat unusual, but plausible explanation why some fields end up with more men than women (as most of the engineering fields do). The theory is that women are more discouraged by a B in an entry-level course than men are (she cites some data from econ courses that support that theory, though it is only correlation, not necessarily causation).

Plenty has been written about whether hostility toward female students or a lack of female faculty members might be pushing women out of male-dominated majors such as computer science. Arcidiacono’s research, while preliminary, suggests that women might also value high grades more than men do and sort themselves into fields where grading curves are more lenient.

As parents and teachers we encourage children to pursue fields that they enjoy, that they are good at, and that can support them later in life. It may be that girls are getting the “that they are good at” message more strongly than boys are, or that enjoyment is more related to grades for girls. These habits of thought can become firmly set by the time students become men and women in college, so minor setbacks (like getting a B in an intro CS course) may have a larger effect on women than on men.

I’m a little wary of putting too much faith in this theory, though, as the author exhibits some naiveté:

But I fear that women are dropping out of fields such as math and computer science not because they’ve discovered passions elsewhere but because they fear delivering imperfection in the “hard” fields that they (and potential employers) genuinely love. Remember, on net, many more women enter college intending to major in STEM or economics than exit with a degree in those fields. If women were changing their majors because they discovered new intellectual appetites, you’d expect to see greater flows into STEM fields, too.

It is very difficult for students, male or female, to transfer into STEM majors late—the number of required courses and prerequisite chains are too long.  As long as the humanities majors have few, unchained requirements and STEM majors have many, chained requirements, the transfer out of STEM will be far larger than the transfer into STEM. Expecting equal flow in both directions is naive.

But there is, I believe, a greater proportional loss of women from STEM fields in college than men, and most of the interventions trying to reduce that loss have not been very effective.  (Harvey Mudd has had some success, attributed to various causes.) If the theory put forth by Rampell is valid, what interventions might be useful? Here are a few I thought of:

• Higher grades in beginning classes. Engineering courses generally average 0.4 or 0.5 grade points lower than the massively inflated grades in humanities courses. I doubt, somehow, that many engineering faculty will be comfortable with the humanities approach of giving anyone who shows up an A, no matter how bad their work. So I don’t think that this idea has any merit.
• Lower entry points. One of the things that Harvey Mudd did was to require every freshman to take CS and to introduce a lower-level CS course for those who did not have previous programming. By having some lower-level courses, students could get high grades in their first course without teachers having to water down existing classes or engage in grade inflation. By requiring the course of all students, students who avoided the subject for fear of not being able to compete are given a chance to discover an interest in the field (and, apparently, many women at Harvey Mudd do discover an interest in CS as a result of the required course).
• Extra tutoring help for B students in entry-level courses. Almost all the “help” resources at the University seem to be aimed at getting students from failing to passing—but the students who are barely passing after massive help do not make good engineering majors, and are likely to fail out of the major later on. It would be far more productive to try to turn the Bs into As, retaining more women (and minorities) in the field. Of course, this means that the assistance has to be at a higher level than it often is now—the tutors need to know the material extremely well and be able to assist others to achieve that expertise.  Basic study skills and generic group help may be good for getting from failing to passing, but may not be enough to get from B to A.
• More information to students about the feasibility and desirability of continuing with a B. This sort of encouragement probably has to happen one-on-one from highly trusted people (more likely peers than adults).

These ideas are definitely half-baked—I’m not even fully convinced that the theory behind them is valid, much less that they would have the desired effect. I welcome comments and suggestions from my readers.

Three Days of Rain

We just saw a very good production of Three Days of Rain, by the Jewel Theatre in Santa Cruz. It runs for another week (Wed through Sun), and I don’t think that all the performances are sold out, so tickets may be available (though probably not for all performances).

We’ve also purchased our tickets for Jewel Theatre’s production of What the Butler Saw in May—for once we ordered the tickets early enough to get our choice of seats.  We picked a day that has apparently just been added to the run, since we were the first to buy tickets for it—the first day we looked at would have required us to sit in the back row, where we usually end up. Those are not bad seats in a tiny theater like Center Stage, but it’ll be a nice change to sit in the third row, in what are arguably the best seats in the house.  (The second row is clearly the worst, since it is on the same level as the first row, so sight lines are somewhat blocked.)

Next year, my wife and I will probably get season tickets for Jewel Theater, as long as most of the plays look like ones we want to see. My son will be away at college (I hope—we haven’t heard back yet from any of the colleges he applied to), so it will just be the two of us. That means we’ll stop skewing the age distribution so much—we’re guessing that my son was the youngest person in the audience by a factor of 2, and my wife and I were probably still below median age and will probably continue to be until we retire.

I think it is a shame that Jewel Theatre is not attracting a younger audience—the ticket prices are fairly affordable ($31 for adults, $26 for students) and the quality is high. Maybe Friday nights get a younger crowd than Sunday nights, and we’re getting a distorted view of the audience age distribution. There is certainly plenty of youth interest in live theater, but maybe it is being met by all the children’s and teen theater that is available in Santa Cruz (schools, West Performing Arts, and the musical companies: All About Theater, Kids on Broadway, Hooked on Theater, Little People’s Repertory Theatre, Christian Youth Theater, …). Perhaps Jewel Theatre needs to team up with West Performing Arts to have a special teen day or family day with discount group tickets.

Poetry Aloud

Sometimes on half-hour bike ride into work, I think up new courses that the university “needs”.  Once in a while I get an opportunity to create such a course—sometimes as part of my regular teaching load, sometimes by taking it on as overload.  I have created many new courses over the years.

Sometimes, the course ideas I come up with are ones that I’ve not really qualified to teach. In some cases, I teach myself the necessary material and create the course anyway: the Bicycle Transportation Engineering course I taught once; “The Art of the Book in the Computer Age” on digital typesetting, when it first became cheap and easy enough for people to do their own; algorithms for digital synthesis of music (OK,  I did know enough to teach that one without more study); technical writing for computer engineers; resource-efficient programming; applied circuits for bioengineers; banana slug genomics; …

Sometimes when I create a course students see no need for it, and it dies for lack of sufficient audience (I have done several of those over the decades). Others end up becoming a standard part of the curriculum (the tech writing course I created with a co-instructor about 26 years ago is now taught every quarter—luckily I only taught it for a little over a decade).

But sometimes the course idea is one that doesn’t rise high enough on my priority list and isn’t a good fit with my department.  It is not worth my time to learn how to teach such classes, but what should I do with the ideas for them?

Here’s an example: Wednesday morning, on my ride up the hill, I came up with a course title: Poetry Aloud.  The idea is a simple one—an interdisciplinary course combining 3 topics:

• Poetics: the study of the structure and technical aspects of poetry, that is, rhythm and meter; assonance, alliteration, and onomatopoeia; formal forms; …
• Poetic content: metaphor, simile, imagery, emotion, word play, allusion, …
• Performance: voice projection, gesture, use of microphone, conveying emotion in the voice, timing, stage presence, performing for video, props, …
• (One could add a fourth component—typesetting poetry—but I think that would dilute rather than enhance the course.)

I’m not thinking of single-genre performance classes (like poetry slams or Shakespearean acting), but of something that spans the gamut from early modern English to the latest song lyrics.

The first two topics comprise a fairly conventional poetry class, and I’m sure that there are courses that include them on campus already.  But I don’t know of any that combine the literary analysis with professional acting skills, to make performance of poetry a central part of the course, along with reading, analyzing, and writing poetry.  I don’t even know how such a course would get created on campus, with the acting teachers and the literature teachers in departments under different deans, located miles apart on campus. Perhaps it would take one of the literature faculty who works as a dramaturge to bring the faculty with the necessary skills together.

This particular course idea is a throwaway one—I’ll never follow up on the idea and will forget it in a week or two. After all, I’ve not written poetry for 30 or 40 years and have never performed poetry.  I don’t plan to start either.

But what should I do with ideas like this that I think (at least for a while) are worth considering, but that I don’t have the skill, energy, time, or resources to pursue?

 

Guessing correction is not guessing penalty

It bothers me that even the New York Times, in an otherwise excellent article repeats a common misperception:

Students were docked one-quarter point for every multiple-choice question they got wrong, requiring a time-consuming risk analysis to determine which questions to answer and which to leave blank.

via The Story Behind the SAT Overhaul – NYTimes.com.

The guessing correction on the SAT meant that you did not have to do any “time-consuming risk analysis”—if you knew nothing about a question, it did not matter whether you guessed or left the question blank—your expected value was zero either way.

Under the no-guessing-correction system, students are forced to guess, or give up 1/5th of a point for each question left blank. Thus the new system rewards gamblers and punishes people who are cautious—rewarding a character trait that should have no influence on test scores.

Under the old system, you could guess randomly on everything you didn’t know if you wanted to—it wouldn’t hurt on average.  Under the new system, you are forced to.  Forced guessing will also penalize those who aren’t aware of time running out, and are forced to “put down their pencils” before getting a chance to randomly bubble the remaining questions. It will also penalize students who would formerly skip difficult questions, then come back to the blank ones later if they had time—leaving a question blank will come with a penalty that wasn’t there before.

I suppose it is too much for me to expected innumerate reporters (even for the NY Times) to know enough probability to understand expected values, but it saddens me that the College Board, in search of higher market share, is giving up on one of the things that they previously were doing correctly.

Sixteenth day: Arduino demo

Today’s class in the freshman design seminar went well. I started by returning the drafts of the design reports and giving some generic feedback. I realized on reading the reports that I had not given a good explanation of what I meant by describing the components of the system—two of the groups had given me long parts lists on the first page of their reports, something that would only really be appropriate in an appendix. I explained that what I wanted was what the main blocks in the block diagram were, and that they should use the block diagram to organize their report, writing a page for each block. I also suggested that they use the block diagram to partition the project among the group members, with each group member working on a different component, then getting back together to reconcile any discrepancies. Note that this is much more like real engineering group work than the usual K–12 group project, which is usually done most efficiently by turning the whole project over to the most competent member of the group.

After the feedback on design reports, I offered the students a chance to get a demo of building an Arduino program with sensing and motor control. This was a completely extemporaneous demo—I had gathered a number of possibly useful components, but had not tested anything ahead of time nor even figured out what order to do the demo in.  I asked the students if they wanted me to start with sensing or control—they asked for the motor control first.

I started by pulling a motor out of box of motors I had gotten when the elementary school my wife works at cleaned out their closets.  I told the students that I had no idea what the spec of the motor were, but since it came from an elementary school, it probably ran on 3v batteries.  I tested the motor by hooking it up first to the 3.3v, then to the 5v power on my Arduino Uno.  It spun just fine on 3.3v, but squealed a bit on 5v, so we decided to run it on 3.3v.

I then pulled out the Sainsmart 4-relay board that I had bought some time ago but never used.  I explained how a relay worked, what single-pole double-throw meant, and normally open (NO) and normally closed (NC) contacts. I used the board unpowered with the NC contacts to spin the motor, then moved the wire over to the NO contacts to turn the motor off.  I then hooked up power to the board and tried connecting input IN1 to power to activate the relay.  Nothing happened. I then tried connecting IN1 to ground, and the relay clicked and the motor spun.  The inputs to the Sainsmart board are active low, which I explained to the students (though I did not use the terminology “active low”—perhaps I should have).  I did make a point of establishing that the relay provides very good isolation between the control logic and the circuitry being controlled—you can hook up AC power from the walls to the relay contacts without interfering with the logic circuitry.

Having established that the relay worked, the next step was to get the class (as a group) to write an Arduino program to control the motor using the relay. With me taking notes on the whiteboard, they quickly came up with the pinMode command for the setup, the digitalWrite and delay for the loop, and with only a tiny bit of prompting with a second digitalWrite and delay to turn the motor back off.  They even realized the need to have different delays for the on and off, so we could tell whether we had the polarity right on the control.  Here is the program we came up with:

#define RELAY_PIN (3)

void setup()
{   pinMode(RELAY_PIN, OUTPUT);
}

void loop()
{
  digitalWrite(RELAY_PIN,LOW); // turn motor ON via relay (or off via transistor)
  delay(1000);  // on for 1 second
  digitalWrite(RELAY_PIN,HIGH); // turn motor OFF via relay (or on via transistor)
  delay(3000); // off for 3 seconds
}

I typed the code in and downloaded it to the Arduino Uno, and it worked as expected.  (It would be nice if the Arduino IDE would allow me to increase the font size, like almost every other program I use, so that students could have read the projection of what I was typing better.)

I then offered the students a choice of going on to sensing or looking at pulse-width modulation for proportional control.  They wanted PWM. I explained why PWM is not really doable with relays (the relays are too slow, and chattering them would wear them out after a while.  I did not have the specs on the relay handy, but I just looked up the specs for the SRD-05VDC-SL-C relays on the board: They have a mechanical life of 10,000,000 cycles, but an electrical life of only 100,000 cycles.  The relay takes about 7msec to make a contact and about 3msec to break a contact, so they can’t be operated much faster than about 60 times a second, which could wear them out in as little as half an hour.

So instead of a relay, I suggested an nFET (Field-Effect Transistor). I gave them a circuit with one side of the motor connected to 3.3V, the other to the drain of an nFET, with the source connected to ground.  I explained that the voltage between the gate and the source (V_GS) controlled whether the transistor was on or off, and that putting 5v on the gate would turn it on fairly well. I then got out an AOI518 nFET and stuck it in my breadboard, explaining the orientation to allow using the other holes to connect to the source, gate, and drain.

I mentioned that different FETs have the order of the pins different, so one has to look up the pinout on data sheet. I pulled up the AOI518 data sheet, which has on the first page “RDS(ON) (at VGS = 4.5V) < 11.9mΩ”. I explained that if we were putting a whole amp through the FET (we’re not doing anywhere near that much current), the voltage drop would be 11.9mV, so the power dissipated in the transistor would be only 11.9mW, not enough to get it warm. I mentioned that more current would result in more power being dissipated (I²R), and that the FETs could get quite warm. I passed around my other breadboard which has six melted holes from FETs getting quite hot when I was trying to debug the class-D amplifier design. The students were surprised that the FETs still worked after getting that hot (I must admit that I was also).

I hooked up the AOI518 nFET using double-headed male header pins and female jumper cables, and the motor alternated on for 3 seconds, off for one second. We now had the transistor controlling the motor, so it was time to switch to PWM. I went to the Arduino reference page and looked around for PWM, finding it on analogWrite(). I clicked that link and we looked at the page, seeing that analog Write was like digitalWrite, except that we could put in a value from 0 to 255 that controlled what fraction of the time the pin was high.

I edited the code, changing the first digitalWrite() to analogWrite(nFET_GATE_PIN, 255), and commenting out the rest of the loop. We downloaded that, and it turned the motor on, as expected. I then tried writing 128, which still turned the motor on, but perhaps not as strongly (hard to tell with no load). Writing 50 resulted in the motor not starting. Writing 100 let the motor run if I started it by hand, but wouldn’t start the motor from a dead stop. I used this opportunity to point out that controlling the motor was not linear—1/5th didn’t run at 1/5th speed, but wouldn’t run the motor at all.

Next we switched over to doing sensors (with only 10 minutes left in the class). I got out the pressure sensor and instrumentation amp from the circuits course and hooked it up. The screwdriver I had packed in the box had too large a blade for the 0.1″ screw terminals, but luckily the tiny screwdriver on my Swiss Army knife (tucked away in the corkscrew) was small enough. After hooking up the pressure sensor to A0, I downloaded the Arduino Data Logger to the Uno, and started it from a terminal window. I set the triggering to every 100msec (which probably should be the default for the data logger), the input to A0, and convert to volts. I then demoed the pressure sensor by blowing into or sucking on the plastic tube hooked up to the sensor. With the low-gain output from the amplifier, the output swung about 0.5 v either way from the 2.5v center. Moving the A0 wire over to the high-gain output of the amplifier gave a more visible signal. I also turned off the “convert to volts” to show the students the values actually read by the Arduino (511 and 512, the middle of the range from 0 to 1023).

Because the class was over at that point, I offered to stay for another 10 minutes to show them how to use the pressure sensor to control the motor. One or two students had other classes to run to, but most stayed. I then wrote a program that would normally have the motor off, but would turn it full on if I got the pressure reading up to 512+255 and would turn it on partway (using PWM) between 512 and 512+255. I made several typos when entering the program (including messing up the braces and putting in an extraneous semicolon), but on the third compilation it downloaded successfully and controlled the motor as expected.

One student asked why the motor was off when I wasn’t blowing into the tube, so I explained about 512 being the pressure reading when nothing was happening (neither blowing into the tube nor sucking on it). I changed the zero point for the motor to a pressure reading of 300, so that the motor was normally most of the way on, but could be turned off by sucking on the tube. Here is the program we ended up with

#define nFET_GATE_PIN (3)

void setup()
{   pinMode(nFET_GATE_PIN, OUTPUT);
    pinMode(A0, INPUT);
}

void loop()
{ int pressure;
  pressure=analogRead(A0);
  if (pressure < 300)
  {    digitalWrite(nFET_GATE_PIN,LOW);  // turn motor off
  }
  else
  {   if (pressure>300+255)
      { digitalWrite(nFET_GATE_PIN,HIGH);  // turn motor on full
      }
      else
      {    analogWrite(nFET_GATE_PIN,pressure-300); // turn motor partway on
      }
  }
}

Note: this code is not an example of brilliant programming style. I can see several things that I would have done differently if I had had time to think about the code, but for this blog it is more useful to show the actual artifact that was developed in the demo, even if it makes me cringe a little.

Overall, I thought that the demo went well, despite being completely extemporaneous. Running over by 10 minutes might have been avoidable, but only by omitting something useful (like the feedback on the design reports). The demo itself lasted about 70 minutes, making the whole class run 80 minutes instead of 70. I think I compressed the demo about as much as was feasible for the level the students were at.

Based on how the students developed the first motor-control program quickly in class, I think that some of them are beginning to get some of the main ideas of programming: explicit instructions and sequential ordering. Because we were out of time by the point I got to using conditionals, I did not get a chance to probe their understanding there.