Explain what mathematics causes an average to move down when a single lower number is added, but the average does NOT move up when two higher numbers is added? That’s what was demonstrated to me. What mathematical phenomenon is that?
Thanks, your math is appreciated and makes sense. I’ll use this template as the reviews continue, to validate Airbnb’s method
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I’m going to bookmark this post and hope I remember it next time someone asks about this. It’s not uncommon for people to have this complaint. I know I’m still smarting over the one star that was given accidentally years ago. I’ve literally had hundreds of reviews since and I’m still stuck at 4.98.
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I could illustrate it to you with a white-board/chalk-board really easily, but the reason is this: When you have an average and you add a new value into that average, the impact of the new value is proportional to the difference between the new value and the average.
To take your example again: When your average was 4.91, your next review was a 4.00. The difference between 4.00 and 4.91 is 0.91. However, if you had instead received a 5.00, the difference between 4.91 and 5.00 is only only 0.09. Comparing those two differences is where you can see the impact: 0.91 is literally more than 10 times bigger than 0.09, which means it has 10 times more impact. Put another way, at that point in time, you would need 10 5-star reviews to “move the needle” as much as 1 4-star review. Back to your example, the single 4-star review dropped your overall rating by 0.03 from 4.91 to 4.88. However, if you had instead received 10 5-star reviews in a row, your rating would’ve increased by 0.03 from 4.91 to 4.94.
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Brian, you illustrated it nicely. My prior question was for Ken. But I appreciate you breaking down the math.
It would take 400 five star reviews to get back to 5.0 after a single one star review. 4.98 is great!
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I think so too. That one star just stung because it was an accident. I also have a 3 star and some 4 stars.
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Well. Well, Well… you guys aren’t going to believe this. My next review came in for this property. And as I mentioned here, I’ve been watching it like a hawk to see what impact each review has. Get this! I got another 5 star rating, and my rating on this property is now a 4.86!!! It moved DOWN from 4.88!! There were no other reviews, just 5 stsrs for the last 3 guesrs, and my score went down. Now I KNOW there is no mathematical phenomenon to explain this. I’m pretty ticked so I called Airbnb. The first rep had me on hold a while and then the call suddenly disconnected. No call back. So now I’ve called back and am on hold with the rep. I’d really like to see how they explain this. SMH.
What say you to the fact that a 3rd 5-star review has sent my score down from a 4 88 to a 4.86? Something is going on and I’m going to get to the bottom of it.
OK, that’s strange. I’m curious.
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Aren’t the ratings done on the last 12 months? You have a total number, but the last 12 months is what counts….how many fell off?
This, it’s a moving average over the last 12 month.
So if you gain a 5 star, but another 5 star moved out of the 12 month window, the average will stay the same.
I think it is a good system, it gives you a chance to increase and loose the low ratings.
Ofcourse now with COVID-19 this could also backfire because you have less reviews.
Due to being closed for 9 months my rating went up from 4.7 to 4.9. The main reason is skipping the low season with all the difficult guests.
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I haven’t had a 4 star rating since summer of 2019. 110 straight 5 star reviews and my average is 4.98.
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I have 2 different ratings.
I can See a 4.77 average over 678 Reviews and a 4.92 over the Last 12 months.
Seems COVID is going to make me a superhost…. But I probably jinxed it now…. 
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I do t think that sliding date period is for the listing rating, just for super host.