GetPercent

Posted by jns on 13 February 2008

The website GetReligion discusses press coverage of news stories about religion, and how well they exhibit an understanding of the religious issues involved. Their name comes from the idea that “The press…just doesn’t get religion.”

Well, in this little example I’m afraid there’s a bit of a need for some GetMath. In a story called “Define social justice — give at least one example“, Mark Stricherz is discussing a story about Jeremiah Wright Jr., the pastor of the church Barack Obama belongs to. I have no issues with the analysis, just with this excerpt

As Ramirez noted, plainly but aptly,

“Obama was one of the thousands who joined Trinity under Wright’s leadership. When Wright became Trinity’s pastor in 1972, the church had 85 members. Today, Trinity has a congregation of 8,500, with more than 80 ministries, making it one of the largest and most influential black churches in the nation.”

In other words, during his tenure Wright’s congregation increased by more than 1,000 percent.

Of course, one notes that Wright’s congregation increased by well over well over 1,000%. In fact, it increased by 10,000%. In other words, it increased by a factor of 100.

To move from a fractional factor, say 0.45, to an expression in percent, one multiplies by 100. Thus, 0.45 of something is also said to be 45% of that something. To move from an expression in percent to a decimal fraction, divide the percent figure by 100. Thus, 32% of something is 0.32 times that something.

This works even if the fractional part is greater than the something being compared to, it’s just that the decimal expression is greater than 1, and the percent expression is greater than 100%. This general expression

where is the percent expression, is what I’ve called the fractional part, and is the amount being compared to, works regardless of whether the “quantity” is greater than or less than the “comparison” value.

So, in Mr. Wright’s case, his congregation, in going from 85 to 8,500 increased by a factor of 100, or by

I expect Mr. Stricherz knows this and simply mistyped, but it did provide me an excuse for a little pedantic moment of the type I love so much.