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Hello All,
I need some clarification on % difference between to numbers vs difference of % points.
A survey found that on average, 34% of students had failed a college level psych course between 2012 and 2015.
After changing the lead instructor, the failure rate was 21%.
Can anyone tell me the % decrease in failure rate? Is it similarly 13% or is it a 38% decrease. Thanks.
Just for balance, remember that those schools you went to were supposed to teach you this back in fifth and sixth grades. Public schools in USA are a major flop and have been for a very long time.
Get a ruler in your hands. Measure things until you start to understand how a ruler works. Measure some stuff and figure out where the center is. Say you measure a book and it's 7/8" thick. You look at your ruler and see that every eighth is divided into two sixteenths, so obviously half of 7/8" is going to be 7/16". If you write that out you have 1/2 x 7/8 = 7/16. And you notice that 1/2 is divided into 2/4 and then into 4/8 and so on, so you can convert anything to anything by multiplying all the numbers on top and then all the numbers on bottom.
Other rulers are divided into 10 and 100 parts. But an inch is still an inch, so anything on one ruler can be translated to the other ruler. A half inch on one ruler is 5/10 or 50/100 on the other. An eighth inch is just 12.5 marks when you have 100 marks per inch. A metric ruler divides an inch into 25.4 parts, so a half inch would be 12.7 of those parts. Pretty simple, isn't it? Practice this a bit and people will think you went to wizard school.
Percent is simply a ruler with 100 marks. The only confusion is trying to keep track of what the marks represent, since that changes from time to time. In your example the change would be expressed in percentage points, since an analysis of failure rate would have to include a new definition for what you call "failure rate" and how it differs from the old failure rate. That is confusing, so you just call it 13 percentage points.
