Fallout 4

Every day we count how many positive and negative reviews were written on Steam for the game (all languages, both Steam purchases and keys), using Steam's public reviews API. A day counts as an anomalous spike only if, within the last 30 days, all of these conditions hold:

• at least 50 negative reviews on that day, so games with few reviews do not trigger the alarm (once a spike has started, it continues as long as the other conditions hold, even below this figure);
• negative reviews are at least 3 times the median of the previous 28 days and exceed the “median + 5 × MAD” threshold (MAD is the median absolute deviation: it measures how much the counts usually vary, without being dragged by a single odd day);
• the share of negative reviews rises by at least 20 percentage points compared with the previous 28 days and exceeds 50%;
• positive reviews do not grow in the same way: compared with usual, negative reviews increase at least 3 times more than positive ones. Releases, big updates and sales also bring lots of positive reviews, so they do not count as a spike.

The comparison needs at least 21 days with reviews among the previous 28: for games that have just come out we give no verdict. Days already flagged are left out of the comparison for the following days, and flagged days close together form a single spike. The score without the spike removes all reviews, positive and negative, written on the spike days (as Steam does when it excludes a period of “off-topic review activity”). Days are in UTC.

This is not a judgement on the reviews: a spike also contains sincere criticism. We only point out that on those days far more negative reviews than usual came in.