CR:the violent crime rate

[Suapplle]

a GMAT prep question
The violent crime rate (number of violent crimes per 1,000 residents) in Meadowbrook is 60 percent higher now than it was four years ago. The corresponding increase for Parkdale is only 10 percent. These figures support the conclusion that residents of Meadowbrook are more likely to become victims of violent crime than are residents of Parkdale.
The argument above is flawed because it fails to take into account

A. changes in the population density of both Parkdale and Meadowbrook over the past four years
B. how the rate of population growth in Meadowbrook over the past four years compares to the corresponding rate for Parkdale
C. the ratio of violent to nonviolent crimes committed during the past four years in Meadowbrook and Parkdale
D. the violent crime rates in Meadowbrook and Parkdale four years ago
E. how Meadowbrook's expenditures for crime prevention over the past four years compare to Parkdale's expenditures

OA:D

I am confusing about the phrase "residents are more likely to become victims of violent crime"
If the total number of violent crime is high,the residents are more likely to become victims of violent crime"
Or
If the violent crime rate is high,the residents are more likely to become victims of violent crime"?
Please help,thanks!

[RonPurewal]

If you just think about this one for a while, you'll figure it out.
If you're posting this kind of question on a forum, then you probably haven't thought about this enough on your own. Just think about a few examples:
* Say the number of accidents in Chicago is higher than the number of accidents in San Francisco. Does that mean you're more likely to get in a crash in Chicago? (Not necessarily; it could just mean that Chicago has more people on the road.)
* Say the accident rate -- i.e., number of accidents per driver or per mile driven -- is higher for Chicago than for San Francisco. Does that mean you're more likely to get in a crash in Chicago? Yes (unless there are other factors -- weather, etc. -- that the study failed to take into account.)

The entire purpose of per-capita statistics, such as crime "rates", is to reflect the likelihood of an event. So, there you go.

--

[RonPurewal]

By the way, if a statistics-based CR problem isn't immediately intuitive, try writing an analogy for the problem, using statistics and concepts that are easier for you to think about.

E.g., here's an analogy for this problem:
Sue's salary is 60% higher than it was four years ago. Tom's is only 10% higher. Therefore, Sue is more likely than Tom to be doing well financially.
--> In this case, I'm betting it's pretty obvious why we would need to know what their salaries actually were four years ago (i.e., choice D).
As I'm sure you'll also agree, this reasoning doesn't depend on quibbling over exactly how "doing well financially" is defined. (So, at the end of the day, the question in the original post doesn't matter much.)

[NitinG177]

hello Ron,

If i use the following analogy ,
e.g
M = meadowbrook
P= parkdale

ratio of crimes M: P = 100: 200

M -->1000 --> 100 (four years ago) --> 160 (now : 60% more)
P -->1000 --> 200 (four years ago) --> 220 (now : 10% more)

then its clear that D is the clear winner here. But for the above analogy to hold
we need to assume that the population is not only constant but also close in magnitude .

I thought the correct answer should take into account this assumption .
IMO,
Choice A is able to fill this gap of actual population.
Please let me know as to what am i missing ?

Thanks,
Nitin

[RonPurewal]

ok, so, first of all, you should not need to 'plug numbers' on verbal problems.
even when the problems deal with statistics, the point is that you should INTUITIVELY UNDERSTAND what the statistics do (or don't) represent, WITHOUT having to 'plug in values'.

e.g., let's say that
...my net worth goes up by 60 per cent,
...bill gates's net worth goes up by 10 per cent.
does this mean i'm richer?
ha ha.
(in fact, even if bill gates's net worth goes down by 99.999 per cent it will still be many many times greater than mine.)

clearly you don't need to plug actual numbers to understand this example. all you need is the intuitive understanding of 'percent changes don't tell me how big things are'.

[RonPurewal]

...now, as far as choice A is concerned, there are two very serious flaws in your approach.


1/
you're either (i) thinking of the wrong statistic, or else (ii) badly misinterpreting the actual statistic:

But for the above analogy to hold
we need to assume that the population is not only constant but also close in magnitude .

nope.
in fact, THE ENTIRE REASON FOR EXPRESSING STATISTICS AS RATES PER PERSON (or per 1000 people, or per square mile, or per whatever) is to MAKE ABSOLUTE NUMBERS IRRELEVANT.

if you were looking at actual numbers of crimes, THEN population figures would be relevant.

when we look at rates per 1000 people, we are very specifically ELIMINATING population as a relevant factor.

just think about it:
'30 crimes per 1000 people' means exactly the same thing about the likelihood/incidence of crime, regardless of the size of a city. this figure means exactly the same thing for small cities as for large ones.


and...

2/
you're not reading the words that are actually there.

choice A isn't even about population at all. it's about population density.

population is already irrelevant (as discussed above), but population density is, like, double irrelevant. (: