# Challenge difficulty

## What is it?

For every Challenge checker in the system there is a *Challenge difficulty* calculated. The difficulty is based on on how many Geocachers fulfill the challenge or not. Project-GC is running Challenge checkers in the background for tens of thousands of Geocachers, this process is a part of the Auto-Challenge-Checker System. The result of these runs is used to calculate the *Challenge difficulty*.

## How is it calculated?

Basically the *Challenge difficulty* tells us what proportion of Geocachers fulfill a challenge or not. The rating is an integer between 0 and 100, but should not be confused with percent. First off it's important to understand that the automatic challenge checker runs aren't automatically executed on the average Geocacher, but more likely on the more hardcore Geocachers. It's primarily executed on Geocachers with more finds, regular users of Project-GC and also paid members of the site. With this in mind we know that the result isn't representing the average geocacher, on the other hand, challenges generally aren't targeting the average geocacher either.

The Challenge checker results are dividing into three categories:

- Region - Geocachers that are determined to live in the same
**region**as the Challenge itself. - Country - Geocachers that are determined to live in the same
**country**as the Challenge itself, but not in the same region. - World - All others

For each category a percentage of how many fulfill the Challenge is calculated. Then the results for each group is weighted different in the calculations, basically a list is created and the percentages are added into that list. A fourth factor is also added into the mix, the number of finds per day.

The number of finds per day isn't used as the raw number itself, but rather as '(1-($numFinds/$daysOld))*100'.

Then the difficulty is calculated as '$difficulty = (3*$worldPercent + 5*$countryPercent + 10*$regionPercent + $findsPerDay) / (3+5+10+1)'.

It should also be noted that there usually are more calculated challenge checker results in the system from more local Geocachers than from those living far away.

### Example

- The Challenge is placed in Texas, United States.
- 80% of the Geocachers in Texas fulfill it.
- 40% of the Geocachers in the other states of the United States fulfill it.
- 30% of the Geocachers in the rest of the world fulfill it.
- The challenge is one year old (365 days) and have had 10 finds during this period.
- Then to weigh these differently using coefficients a sum is created like this: 3*80+5*40+10*30+((1-(10/365))*100).
- This sum is then divided by 19 (3+5+10+1, the last being related to findsPerDay).
- The
*Challenge difficulty*ends up being 837.26/19 = 44.066, which is rounded down to 44. The values are always rounded down to the closest integer.

## Related statistics

Challenge difficulty per rating interval shows the correlation between the difficulty rating of the geocache and the challenge difficulty.