The relationship between accuracy, precision, and relevance

OK, this is a rant.

graph1It annoys me to no end when people present graphs like this one. Yes, the numbers do in fact add up to 100% but does it make any sense to have so many digits after the decimal when in reality this is based on a sample size of 6? Wouldn’t 1/2, 1/3, 1/6 have sufficed? What about 0.5, 0.33 and 0.67. Do you really really have to go to all those decimal places?

Excel has made it easy for people to make meaningless graphs like this, where merely clicking a little button gives you more decimal places. I’m firmly convinced that just having more digits after the decimal point doesn’t really make a difference in a lot of situations.

Let’s start first with some definitions

accuracy is a “degree of conformity of a measure to a standard or a true value“.

precision is the “the degree of refinement with which an operation is performed or a measurement stated“.

One can be precise, and accurate. For example, when I say that the sun rises in the east 100% every single day, I am both precise, and accurate. (I am just as precise and accurate if I said that the sun rises in the east 100.000% of the time).

One can be precise, and inaccurate. For example, when I say that the sun rises in the east 90.00% of the time, I am being precise but inaccurate.

So, as you can see, it is important to be accurate; the question now is how precise does one have to be. Assume that I conduct an experiment and tabulate the results, I find that 1/2 the time I have outcome A, 1/3 of the time I have outcome B, and 1/3 of the time I have outcome C. It would be both precise, and accurate to state the results are (as shown in the pie chart above) 50.0000%, 16.66667%, and 33.33333% for the various possible outcomes.

But does that really matter? I believe that it does. Consider the following two pictures, these are real pictures, of real street signs.

2018-08-16 18.18.09

This sign is on the outskirts of Mysore, in India.

2018-09-08 10.37.06

This sign is in Lancaster, MA.

In the first picture (the one from Mysore, India), we have distances to various places, accurate to 0.01km (apparently). Mysore Palace is 4.00 km away, the zoo is 4.00 km away, Mangalore is 270.00 km away. What’s 0.01km? That’s about 10m (about 33 feet). It is conceivable that this is accurate (possible, not probably). So I’d say this is precise and may be accurate.

The second picture (the one from Lancaster, MA) is most definitely precise, to 4 places of the decimal point no less. The bridge is 3.3528 meters (the sign claims). It also indicates that it is 11 feet. A foot is 12 inches, an inch is 2.54 centimeters, and therefore a meter (100cm is 39.3701″) is exactly 3.2808 feet. Therefore 11 feet is 3.3528 meters exactly. So this is both precise, and accurate (assuming that the bridge does in fact have a 11′ clearance).

The question is this, is the precision (4.00km, or 3.3528m) really relevant? We’re talking about street signs, measuring things with a fair amount of error. In the case of the bridge, the clearance could change by as much as 2″ between summer and winter because of expansion and contraction of the road surface (frost heaves). So wouldn’t it make more sense to just stick with 11′, or 3.5 meters?

So back to our graph with the 50.0000%, 16.66667% and 33.33333%. Does it really matter to the person looking at the graph that these numbers are presented to a precision of 0.000001%? For the most part, given the fact that the experiment had a sample size of 6, absolutely not.

So please, when presenting facts (and numbers) please do think about accuracy; that’s important. But please make the precision consistent with the relevance. When driving a car to the zoo, is the last 33′ going to really kill me? or am I really interested in the clearance of the bridge accurate to the thickness of a human hair, or a sheet of paper?

 

Android in a virtual machine

Very often, I’ve found that it is an advantage to have Android running in a virtual machine (say on a desktop or a laptop) and use the Android applications.

Welcome to android-x86

Android runs on x86 based machines thanks to the android-x86 project. I download images from here. What follows is a simple, step-by-step How-To to get Android running on your x86 based computer with VMWare. I assume that much the same thing can be done with some other emulator (like VirtualBox).

Install android-x86

The screenshots below show the steps involved in installing android-x86 on a Mac.

android-x86-1

Choose “Create a custom virtual machine”

android-x86-2

Choose “FreeBSD 64-bit”

android-x86-3

I used the default size (for now; I’ll increase the size later).

android-x86-4

For starters, we can get going with this.

android-x86-5

I was installing android v8.1 RC1

android-x86-6android-x86-7

Increased #cores and memory as above.

android-x86-8

Resized the drive to 40GB.

android-x86-9

And with that, began the installation.

Options during installation.

The options and choices are self explanatory. Screenshots show the options that are chosen (selected).

android-x86-10android-x86-11android-x86-12android-x86-13android-x86-14android-x86-15android-x86-16android-x86-17android-x86-18android-x86-19android-x86-20android-x86-21android-x86-22android-x86-23android-x86-24

One final thing – enable 3D graphics acceleration

Before booting, you should enable 3D graphics acceleration. I’ve found that without this, you end up in a text screen at a shell prompt.

android-x86-26

And finally, a reboot!

android-x86-25

That’s all there is to it, you end up in the standard android “first boot” process.

What I learned photographing a wedding

Recently, I had the opportunity to photograph a wedding. Some background for people reading this (who don’t have the context). The wedding was an “Indian wedding” in San Francisco, CA. It was a hybrid of a traditional North Indian and a South Indian wedding, and was compressed to two hours. There were several events that occurred before the wedding itself, and there were a few after the wedding.

San Francisco skyline

For example, there was a cruise around the San Francisco Bay (thankfully, good weather).

San Francisco Bay Bridge

There were also several indoor events (which were conducted in a basement, and Lord Ganeshaso little natural light). There were several religious ceremonies, a civil ceremony, and lots of food, and drink, and partying as well.

Before heading out to SFO, I read a bunch of stuff about photographing weddings, and I spoke with one person (Thanks Allison) very familiar with this. I took a bunch of gear with me, and I thought long and hard about how to deal with the professional photographer(s) who would also be covering the event.

I was hoping that I’d be able to work alongside them, and watch and learn (and not get in the way). I hoped that they’d not be too annoyed with a busybody with a bunch of gear, and I hoped that I could stay out of their way.

Thinking back, and looking at the pictures I took, I’ve learned a lot; a lot about taking photographs, a lot about myself, and a lot about the equipment that I have.


Shoot fully manual mode – most of the time

Outdoors, it may be possible to get away with auto ISO, but even there shooting anything other than manual focus, manual exposure and aperture is a bad idea. I’ve tried a number of different options for metering, and focus preference, but did not find them to be particularly fun. But, that did mean that I was shooting stopped down (f5.6 or smaller).

Bounce the flash off the roof

I used a Nikon Speedlight SB-700 and if I didn’t bounce it off the roof, the foreground subject got over exposed. Using the diffuser, and bouncing the flash off the roof produced much better results.

You do really want f2.8 a lot of the time!

While I often shot f5.6 or smaller, I did find myself shooting f2.8 quite a lot. Not as much as I thought I would, but certainly quite a lot. And it was good that I had lenses that could go to f2.8. Most of the time I found that I was shooting between 50mm and 90mm so it was quite annoying that I needed two lenses to cover this range. But I managed …

Shoot RAW (+JPEG, but definitely RAW)

I’ve found that many of the pictures I took needed Benefits of shooting RAWpost-processing that would was much easier with RAW. For example, some of them required significant color (temperature) and exposure adjustment.

One example is at left, I think the color temperature of the picture above is better than the one below. The significant amount of purple in the decorations caused the image to look a little bit too purple for my liking. Luckily the little white altar in the foreground gave me a good color reference.

I don’t want to get into the “can this be done with JPEG” debate; I’m sure that it can, and there are many who prefer JPEG. I just feel lucky that I shot everything RAW+JPEG.

LED Light Panels are a must

I have a great flash, but it is no match for a good LED light panel. I really need to get one of those things if I’m ever going to shoot a wedding, or any other event with a lot of people.

Take more pictures; way more pictures

I’m not a “spray and pray” kind-of person. I tend to look through the view finder a while before clicking. I try to frame a shot well, get everything to look just right, and then the subject has moved, or the ‘moment’ has passed. This happened a lot.

I really have to learn to accept a lower ‘good picture’ ratio, and capture the moment as best as I can, and crop, and post-process later.

Lose a lot of weight

The professionals were at least a hundred pounds lighter than I was. The way they moved clearly reflected a certain difference in our respective ‘momentum’s!

I definitely need more experience with photographing people, something that I’ve known for a while. The wedding was a great excuse for me to happily point a camera at people who were having animated conversations, and click. Now I have to find other venues where I can do the same thing, and learn more about this aspect of photography that I’ve really neglected for too long.

P.S. My thanks to Allison Perkel for all the pointers she gave me before I went on this trip.