How would YOU compute IMDB movie rating?

Question

I'm doing this only for learning purposes. I've no intentions of reversing the methods of IMDB.

I asked myself I owned IMDB or similar website. How would I compute the movie rating?

All I can think of is Weighted Average(which is nothing but Arithmetic Mean)

For a movie data provided below computation would be

(38591*10 + 27994*9 + 32732*8 + 17864*7 + 7361*6 + 2965*5 + 1562*4 + 1073*3 + 891*2 + 3401*1) / 134434 = 8.17055953

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My rating 8.17055953 doesn't match with IMDBs rating (=weighted average). So my conclusion is I'm missing something here or my score is not an ideal score. I'm might be missing lot of things.

1. Whats wrong with my score? Why is it not ideal?
2. If you had to compute. How would you have done it?

Answer 1

Not exactly on topic, but useful for you:

How the ranking is calculated.

I hope that helps.

P.S. This is confirmed on this page:

IMDB Chart