Formula for rating system

richie

Hello,

I'm developing a custom blog, and I need to calculate a rating for each blog entry.

I'm stuck on what formula to use for the rating.

Let's say 10 people voted for a blog on a 5 star system...

3 people gave 5 stars
4 people gave 4 stars
1 person gave 3 stars
2 people gave 2 stars
0 gave 1 star

How do I calculate the effective stars for that blog?

I thought of mean value, i.e. taking the total number of stars, and dividing that by the aggregate number of voters.

35 = 15 stars
44 = 16 stars
13 = 3 stars
22 = 4 stars

Total # of stars = 38 stars
Total number of votes = 3+4+1+2 = 10

Average # of stars = 38/10 = 3.8

Is this the correct way to calculate this stuff?

Also, what do you recomment to use on the fraction:

floor()
round()
ceil()

TIA.

coldwerturkey

Yeah (to me) that seems fine. I would use round() because if the blog was 4.4 you want it to go to 4 and if its 4.6 you want it to go to 5

richie

Thank you.

It's always good to gain other people's perspective on things before implementing it, particularly when one is only doing it for the first time.

katsurace

may be you people are right but what i think is using ceil() floor() or round() is not appropriate method to rank. i dont think its good idea to suppose 4.6==5 and 4.4 != 4.6.

laserlight

katsurace wrote:
may be you people are right but what i think is using ceil() floor() or round() is not appropriate method to rank. i dont think its good idea to suppose 4.6==5 and 4.4 != 4.6.

What do you suggest then? One could have half a star, I suppose, but unless one draws the stars themselves dynamically (and even then), the line has to be drawn somewhere.

richie

Indeed I've seen half-point rating systems here and there. It's something I may look at down the road, but what I have now will do.

To create something like that, one would have to define some thresholds, such as:

if(rating >= 3.2 && rating < 3.8) then rating = 3.5;
if(rating >= 3.8 && rating < 4.2) then rating = ceil(rating);

One could even go more granular into the quarter-point territory.

Yeah, I'll pass on that for now.

Weedpacket

richie wrote:
Indeed I've seen half-point rating systems here and there. It's something I may look at down the road, but what I have now will do.

"Half-point" rating systems are different from "full-point" rating systems in the same way that "100 US cents" is different from "1 US dollar".

"Four and a half points" is the same thing as "Nine half-points" and if you're going to give a ranking of n half-points out of five then you might as well just give a ranking of n points out of ten.