How to correct (adjust) Amazon ratings based on the number of reviews

[Wes Turner]

I would like a way to compare Amazon ratings as a function of the number of reviews. I think it's pretty clear that a product with a 4.9 rating based of 5,000 reviews is likely better than one with a 5.0 rating based on just 1 review. But how can I calculate an adjusted rating for a set of products
such as the ones in this table of ratings and number of reviews.

Thanks

 

[Dale]

Well, you could set a threshold and use a Bayesian approach to assess the posterior probability that the rating is higher than the threshold

 

[Wes Turner]

I don't know what that is or how to do it. Is there a formula I can put in the Adjusted Rating column?

I was thinking about calculating a confidence interval. Here's my first try at that. I calculated the confidence interval using the Excel T-distribution confidence interval function, then subtracted that from the rating.

I then did the same thing using the Excel N-distribution confidence interval function and subtracted that from the rating.

Here's the data for a 95% confidence interval. The last column shows the difference in the rankings from using an N-distribution function vs a T-distribution function.

Any comments? Is there a better way? Should I use a different confidence interval (97%? 99%?)?

Thanks