Does Measurement Measure Up?: How Numbers Reveal and Conceal the Truth

CHAPTER 9: GARBAGE IN, GARBAGE OUT: The Computer and Measurement

CHAPTER 9 GARBAGE IN, GARBAGE OUT The Computer and Measurement Any sufficiently advanced technology is indistinguishable from magic. —Arthur C. Clarke, Profiles of the Future (1973) Google That When I type ‘‘measurement’’ and ‘‘computer’’ into the search line at google.com and hit the return key, I see displayed almost instantly on my screen the names of the first 10 web sites out of ‘‘about 5,110,000’’ that are, to varying (and measurable) degrees, relevant to my request. If I wanted to, I could peruse all 5,110,000 of those sites (or I could first refine my request— even professors don’t have that kind of free time). The technical term for what Google has done for me is a ‘‘miracle.’’ Well, actually that’s not the technical term, but that’s what it seems like to me—a guy who is supposed to know something about technology. Whatever you call it, modern Internet searching involves a lot of mea- D OES M EASUREMENT M EASURE U P ? 168 surement. Google measures the ‘‘relevance’’ of the web pages it provides me with using proprietary software. One of the factors that goes into measuring relevance is the number of links to a given web page from other pages. Each such link is a ‘‘vote’’ for the page being linked to, and some votes are given more weight in the relevance calculation than others— depending on how important the page is that is casting the vote. These web page rankings are combined with a user’s search query, such as mine for ‘‘measurement’’ and ‘‘computer.’’ Google matches my search words to text on the web pages. In doing so, it claims to go ‘‘far beyond the number of times a term appears on a page and examines all aspects of the page’s content (and the content of the pages linking to it).’’ The goodness of the match between the query and a given web page is then combined with that page’s rank to determine where it will fall on the list of matches supplied in response to any given query. Online searching is certainly not the only intersection between the computer and the measurement revolution. The ubiquity of the computer in modern life is hardly newsworthy these days. Computers sit on every workplace desk and fill up the classrooms of most every school. Most of us are likewise aware that computers control a great many functions of many modern machines. A typical car in 2005 is said to contain more computing power than all the computers in the world contained in 1950, and a typical laptop these days is said to be more powerful than the on-board computers used during the Apollo moon missions. Computers (microprocessors is a more precise term) also control telephones, toasters, coffee machines, and a host of other modern conveniences. Statistics and lists like these get a little tiresome, as do the ‘‘remember when?’’ stories of baby boomers like me who did time using punch cards and slide rules. Before I stroll too far down Memory Lane, let’s focus in on the computer and measurement. Three Roles for the Computer in Measurement The role of computers in the measurement revolution is perhaps underappreciated . Computers are phenomenal measuring machines. Strictly speaking, the computer itself does not do the measuring. That is generally done by instruments such as thermocouples (for measuring temperature), force transducers (for measuring force), and a whole universe of other instruments for measuring the frequency and intensity of light and other G ARBAGE I N , G ARBAGE O UT 169 forms of radiation, the strength and orientation of magnetic fields, and so on. While the computer itself does not make these measurements, it does play three crucial roles: data acquisition, data reduction or mathematical manipulation, and numerical simulation. Data Acquisition A computer is extremely good at recording measurements. What a ‘‘recording secretary’’ it is! Working in tandem with the appropriate instruments, a typical desktop computer can record measurements of pressure, temperature , force, and many other quantities tens of thousands of times per second—and faster. This sounds impressive, but it may not be immediately obvious why it is so revolutionary. Things were not always this way. The clipboard, once the constant companion of the data taker, has practically disappeared. Getting the numbers used to be the hard part. Now, once one has the right instrumentation, and the right...