Hire Tom
Mostly Mozart


Lies, damn lies, and statistics
Posted February 13, 2004

Marketing language is special. It's okay to mislead as long as you don't lie. The idea is to make your product sound better than it is, in such a way that you can always claim that what you said was true.

Example: CRT screens and the angry inch

The size of a television or a computer monitor is given in inches from the bottom left to the top right corner of the picture tube. If you measure your 17 inch screen, you'll find only 16 inches between opposite corners. The extra inch is hidden behind the plastic case because the picture quality at the edges of a CRT is so poor.

Obviously, the measurement that matters to the consumer is the size of the picture, not the picture tube.

However, "17 inch" sounds bigger than "16 inch", so the marketing crew calls it a 17 inch monitor. If you try to return your 17 inch monitor because the screen is only 16 inches, the manufacturer will explain that you bought a 17 inch picture tube, not a 17 inch picture.

LCD panels work fine at the edges, so the entire panel is used to display a picture. Therefore, a 17 inch LCD panel is larger than a (so-called) 17 inch CRT screen.

Example: powerful stereo systems

The output power of an amplifier is measured in watts. Louder, better amplifiers output more watts. Each manufacturer wants you to think that its amplifiers are more powerful than their competitors' amplifiers.

The sound quality of an amplifier is measured in %THD (total harmonic distortion). Less distortion is better, so 0.001%THD is better than 0.002%THD. Each manufacturer wants you to think that its amplifiers have less distortion than their competitors' amplifiers.

If you measure both of these figures at the same time, you get a measure of how good your amplifier sounds at a given output power (volume).

Manufacturers do not measure both of these figures at the same time!

First, they connect the speaker terminals to a small device whose electrical characteristics are completely different than those of a loudspeaker. They turn the volume all the way up and measure the output power. 300 watts! Wow. (When the volume is turned all the way up, the total harmonic distortion is very high, so they don't measure it.)

Next, they turn the volume way down and measure the total harmonic distortion. 0.0001%! Wow. (At this point, the amplifier is not producing enough power to drive a speaker, so they don't measure the output power.)

When you read the specifications, you get two measures of quality:

  1. How much power would the amplifier produce if it were driving a resistor instead of a speaker, and sound quality was not important?
  2. How accurate would the amplifier be when if it were driving a resistor instead of a speaker, and the volume were set too low to hear anything anyway?

Obviously, neither of these measures are relevant to someone who wants to listen to music.