Thursday, August 21, 2008

I am very confused...

According to this graphic in CNN Money section, every child has a probability of at least 24% to get into the top 20%. How is this possible?



http://money.cnn.com/2008/08/20/pf/college/college_price.moneymag/index.htm

5 comments:

Yi Li said...

Where did you get the number 24%?

rgrig said...

Either there-s a negative number of children coming from the middle class or you are not supposed to add BA to non-BA percentages (because they are defined with respect to their subsubgroup, not with respect to their subgroup). Take your pick.

Phil said...

It's not at all clear how those percentages even distribute. The total for all income groups together should add up to 20% if it reflects what percentage of population enters the top 20% income earners. Or it should add up to 100% if it is scaled to reflect each family income group's contribution (of children who make it) to the top 20%.

The answer probably comes from looking at the definition of the income groups. They don't represent the full population. The income group from $33,801 to $48,799 and the group from $65,101 to $82,099 are not represented. So the total of these percentages don't mean anything due to missing data.

It is likely the 24% is supposed to be the proportion of bottom family income groups that have a child make it to the top 20%. Given the missing groups, it's hard to know just how many people we are talking about in these groups.

And are they limiting these statistics to all children, or those that have the option to go to college (but may not), or to those that do go to college (but may not finish).

Most likely the statistics were cherry-picked by CNN out of a more complex study that is beyond the average readership of CNN, or wasn't understood well by the journalist who was researching this.

Josh said...

Multivariable: Time is not static. Once you get in the top 20% doesn't mean you will stay in the top 20% which means the fraction who get in exceeds the population at any given time. Thus you can have a higher population that will get in than is actually in at any given time.

That should definately be on the Micrsoft interview. I can definately answer that:)

Casey said...

I love that you posted a screen shot of Firefox. They should send you a cake. HAHAHAHA