IEEE Consultants' Network of Long Island

False Negatives, COVID-19 and Your Rights - John Dunn, Consultant, Ambertec, P.E., P.C.

I was listening to an interview the other day about COVID-19 testing and the likelihood of a "false negative" test result. If I heard the interview correctly, the numbers are rather startling.

Suppose that the likelihood for any one test is that detection of the virus has a 99% or 0.99 probability of being correct for a genuinely infected patient. That would mean a 1% chance of not detecting the virus in a genuinely infected patient, a 1% chance of a false negative test result for that genuinely infected patient.

Yes, I repeated that phrase over and over again for emphasis.

Now suppose you have two genuinely infected patients whom you test. The probability of correctly detecting both infections would be 0.99 x 0.99 = 0.99² = 0.9801 which is a 98.01% probability of correctly detecting both infections and which therefore means a 0.0199 probability, or 1.99% probability of at least one false negative test result.

Now suppose you have three genuinely infected patients whom you test in the same way. The probability of correctly detecting all three infections would be 0.99 x 0.99 x 0.99 = 0.99³ = 0.9703 which is a 97.03% probability of correctly detecting all three infections and which therefore means a 0.0297 probability, or 2.97% probability of at least one false negative test result.

Carry this calculation on to larger numbers of tests and you come to sixty-nine patients for whom 0.99⁶⁹ =  0.4998 which means a false negative probability from someone in the group of 50.01%. As the tested group is made larger, the probability of getting at least one false negative test result gets closer and closer to absolute certainty of 100%.

For example, in testing one thousand infected people:  (1 - .99¹⁰⁰⁰) = 0.99996 which is 99.996% probability of there being at least one false negative test result. If that one false negative person goes out into the community, that one person becomes a new vector of virus transmission to lots of other people.

If only one percent of a total population is infected, then testing one hundred thousand people would yield the same probability of a false negative person going out there and doing harm. The present population of the Borough of Queens in New York City is approximately 2.2 million. Think about the implications of that number.

The lesson we must learn is that a negative test result does not mean the test subject is free to go out there and not wear a mask and not maintain social distancing because that negative test result might be false. If your test result is a false negative and you violate the rules, you can do terrible harm.

To someone who says: "You don't have the right to make me wear a mask and take away my freedom.", I say the following:

"Your freedoms do not give you the right to drive your car with an expired inspection and your freedoms do not give you the right to not wear a mask and thereby risk taking away someone else's life."

Unmet Expectations - John Dunn, Consultant, Ambertec, P.E., P.C.

Maybe I'm getting a little old and cranky, but I find I'm losing my patience regarding some kinds of unmet expectations. I offer two examples, one from many years ago and the other one, quite recent.

Back in 1979, forty-one years ago at this date, I was part of developing the "Bertan High Voltage Enclosure" product called, of course, the "B-HiVE". I just discovered some B-HiVEs for sale on e-Bay and there I found this picture of three of them:

Each B-HiVE could support up to sixteen plug-in modules where each module contained two high voltage power supplies delivering pairs of independently adjustable high voltage outputs of zero to -3 kV, +3 kV, -7.5 kV or +7.5 kV. The high voltage outputs were digitally controllable via an RS-232 port or an IEEE-488 interface.

The internal digital goodies were based on the Intel 8085A with software contained in four 2716 EPROMs. The digital command set could be computer operated, but the commands were kept very simple so that even a "dumb terminal" of that era could be used effectively.

Some years after the B-HiVE was introduced and after B-HiVEs had been in service, mostly for powering large arrays of photomultiplier tubes in a proton decay experiment and for powering proportional wire chambers in particle accelerators, around 1985 if I recall correctly, I took this phone call from a very irate user. He was up in arms over how crude he felt the B-HiVE's control provisions were.

Clearly, as he stated to me in very angered tones, the B-HiVE should have had a built in programming language. "You might at least have made it programmable in FORTH." he intoned. "This thing looks like it was designed in 1978!"

Well, he was off by one year which I took the time to point out, but I never did get this guy to simmer down nor was I able to assuage his unmet expectations. Instead, he hung up the phone on me and I never heard anything more from that quarter. (Bye-bye.)

Now consider the following text which came my way in response to some recent EDN essays that I wrote under the "Living Analog" banner. One essay was about the engineer who lost his cool over a directional coupler design setback and the other essay was about the concept of phase dispersion.

Please take a moment to read this through and don't skip over anything. Let it all sink in.

A little patronization and some personal chest thumping having been noted, if the above writer really wanted to know how many dB down a sideband will drop versus so many degrees of phase dispersion, I'm sure he/she is capable of doing the math. However, I'm not sure that any calculation attempt on my part would satisfy this person's unmet expectations nor do I intend to try.

My EDN essays are not full sized articles. They are not even application notes. By intent and by direction they are merely anecdotal stories garnered from years and decades gone by. It is hoped that now and then they may introduce concepts unfamiliar to the reader. Hopefully too, they may now and then entertain the reader. If either is achieved, I am content.

However, as far as trying to satisfy additional unmet expectations, to be quite blunt, I have neither the inclination nor the skill. I can only ask for forgiveness for that limitation. 

Shower Stall Plumbing - John Dunn, Consultant, Ambertec, P.E., P.C.

This house was built in 1949. After maybe fifty years, the downstairs shower broke down. One of the faucets got jammed and the whole assembly needed replacement. The original configuration was along the following lines:

There were two faucet handles, one for the hot water and one for the cold water. However, the replacement installation was configured differently as follows:

Instead of two faucet handles, there was just one which operated on both the hot water and the cold water. I asked the plumber why this configuration was adopted and he told me that it is a modern code requirement, a code which did not exist back in 1949. The thinking is to help avoid having the following situation take place:

In the older arrangement, the user might unthinkingly turn off the cold water faucet so that only the hot water would be carried up to the shower head. In such a case, the user could be scalded. The single faucet arrangement tends to at least mitigate that possibility.

In retrospect, I suppose I should have seen this for myself, but somehow I did not.

I thought maybe I ought to pass this tidbit of information along, just in case.

Arrrrgh! - John Dunn, Consultant, Ambertec, P.E., P.C.

Sometimes an actor is so intensely effective in a particular role that his or her style of portraying the subject character enters firmly into the popular culture. Think of Boris Karloff as the Frankenstein monster or of Bela Lugosi as the vampire Dracula.

A perhaps lesser remembered but every bit as effective actor was Robert Newton who portrayed the pirate Long John Silver. Take a look at the following YouTube search result and an image I extracted from there to see who and what I mean.

https://www.youtube.com/results?search_query=robert+newton+long+john+silver

Robert Newton (1905 - 1956) was an English stage and film actor. I submit that because of this man, if anyone today wants to make an immediately recognizable image of a pirate, it is necessary to imitate Robert Newton's style of presentation, especially the vocalization "Arrrrgh".

Take a little time out when you need a rest and enjoy some of his work.

One side note:

When I was a child and Robert Newton had his television show "Long John Silver", there was a woman in the cast, Connie Gilchrist (1901 - 1985), who played the role of "Purity Pinker". My parents one day took me and my sister to a luncheonette where I saw a waitress working behind the counter who was an absolute ringer for the character Purity. I tried to point this out to Mom and Dad it was but to no avail. Still, the memory of that moment has vividly stayed with me.

Cynicism - John Dunn, Consultant, Ambertec, P.E., P.C.

There was a "B.C." comic strip some time ago where the cavemen are holding a meeting of a society called "Cynics Anonymous". The caveman Peter is standing at a rock podium addressing the other cavemen who are seated as an audience and he says "Hello. My name is Peter and I'm a cynic." In response, one of the other cavemen in the audience turns to a third caveman sitting next to him and says "Yeah, sure. He's just here to meet women."

Cynical does not equal smart. Quite the opposite for the most part, the habitual cynic is more likely to be deceivable by whoever seeks to play to that trait, often for malicious purpose. Cynicism fosters myriads of conspiracy theories of all kinds.

I once came across the theory that Gerald Ford who served on the Warren Commission after the assassination of President Kennedy had been involved in arranging for the assassination to take place so that he himself could eventually rise to the Office of President. The supposed proof was that Ford had indeed become president.

Sometimes, suspicions of malevolent intent turn out to be justified as in the cigarette industry striving to conceal from general public knowledge, the links between tobacco use and cancers. Think back for example to cigarette advertising that referred to soothing the smoker's "comfort zone".

Learning to distinguish hype from reality turns out to be a difficult matter for a large segment of not just the United States population but of population segments of other nations as well.

I can describe the problem, but I wish I had a clear idea of how to describe the solution, the remedy.

The Fluid Ounce - John Dunn, Consultant, Ambertec, P.E., P.C.

I have many times read that one fluid ounce is the volume of that quantity of water which weighs one ounce. For many years, I have learned this fact and forgotten it again and learned it and forgotten it over and over and over. One day though, just fooling around with some chemistry stuff I happened to have at hand, this fact was permanently etched into my synapses.

I had these calibrated test tubes, a test tube support rack and a scale. I attached a test tube to the rack and weighed that combination. The weight came to 6½ ounces. Then I added just enough water to bring the water level to the 1.0 mark on the test tube and I weighed that combination at 7½ ounces.

The difference between the two weights, 7½ ounces minus 6½ ounces was one ounce which could only be the weight of the water. The volume which we call one fluid ounce is the volume occupied by that amount of water which weighs one ounce.

I had gone from knowing this fact to actually KNOWING this fact and never again did I ever have the experience of forgetting.