Movie Rating Systems

Movie reviews often include a numerical score or letter grade. It can be helpful to compare such ratings from a variety of reviewers and publications, but this is complicated by the fact that different sources use different systems of rating. The following tables show how to interpret scores from the most widely used methods of scoring movie reviews. For each numerical or letter grade in a given system, there is a row with the equivalent average (i.e. estimated or approximate) rating on a 1 – 99 scale. Also displayed on the same row are the minimum and maximum scores, and the corresponding uncertainty, again using a 1 – 99 scoring system.

Some review sites use a 0 or 1 to 100 scoring system. For all practical purposes, these ratings can be trivially converted to a 1 – 99 scale simply by neglecting the tiny discrepancy. Hey, this isn’t rocket science! The advantage of using a 1 – 99 system is that it requires only two display digits, and it allows 0 to be reserved to mean “Unrated”.

Ratings of 1 – 5 whole stars

The following table shows how to convert from 1 – 5 whole stars (or an equivalent 5-valued scheme) to a rating between 1 and 99.

# Stars Avg Min Max Uncertainty
1, Poor 10 1 19 9
2, Fair 30 20 39 10
3, OK/Good 50 40 59 10
4, Very Good 70 60 79 10
5, Excellent 90 80 99 10

Ratings of 0 – 4 stars, with half-stars

The following table shows how to convert from a system that uses 0 – 4 stars, also allowing for half-stars (or an equivalent 9-valued scheme) to a rating between 1 and 99.

# Stars Avg Min Max Uncertainty
0 6 1 11 5
0.5 17 12 22 5
1 28 23 33 5
1.5 39 34 44 5
2 50 45 55 5
2.5 61 56 66 5
3 72 67 77 5
3.5 83 78 88 5
4 94 89 99 5

Ratings of 0 – 5 stars, with half-stars

The following table shows how to convert from a system that uses 0 – 5 stars, also allowing for half-stars (or an equivalent 11-valued scheme) to a rating between 1 and 99.

# Stars Avg Min Max Uncertainty
0 5 1 9 4
0.5 14 10 18 4
1 23 19 27 4
1.5 32 28 36 4
2 41 37 45 4
2.5 50 46 54 4
3 59 55 63 4
3.5 68 64 72 4
4 77 73 81 4
4.5 86 82 90 4
5 95 91 99 4

Academic-style letter grades, with + or -

The following table shows how to convert from a conventional academic letter grading system (F – A), also allowing for +/- qualifiers, to a rating between 1 and 99. Generally, this system omits the letter grade of E, and F is never qualified (i.e. there is no usage of F- or F+).

Grade Avg Min Max Uncertainty
F 10 1 19 9
D- 23 20 26 3
D 30 27 32 3
D+ 36 33 39 3
C- 43 40 46 3
C 50 47 52 3
C+ 56 53 59 3
B- 63 60 66 3
B 70 67 72 3
B+ 76 73 79 3
A- 83 80 86 3
A 90 87 92 3
A+ 96 93 99 3

Ratings with a decimal fraction

A number of sites express movie ratings as a number with 1 digit after the decimal point. For example, while IMDb obtains individual user ratings on a 1-10 scale (whole numbers only), it reports average user ratings with the added precision of a single digit after the decimal point. Similarly, Netflix obtains individual user ratings on a 1-5 scale, but it reports average user ratings with an extra decimal digit of precision. To translate IMDb or Netflix-style average user ratings into their 1-99 equivalents, use this JavaScript-based movie rating conversion tool.

References

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