The ease score is the average rating for all reviews that a given reviewer submits. The average ease score for reviewers of this product is 4.8, while the average ease score for reviewers in this category is 4.2. Based on our statistical modeling, the discrepancy in average rating between these two groups is significant enough to believe that the difference is not due to random chance, and may indicate that there are unnatural reviews.

• 
• 75%
• Have an overrepresented word count

In the graph above, we can see the distribution of review word counts for this product and the expected distribution for this category. We see the following 3 groups with a statistically significant greater concentration than what we'd expect to see:

• 41-65 words: 23.1% (Avg. rating: 4.8)
• 66-100 words: 27.3% (Avg. rating: 4.9)
• 101-200 words: 24.7% (Avg. rating: 4.9)

In total, we found that 338 reviews (or 75%) are within an overrepresented word count group. These reviews have rated this product an average of 4.8, while all other reviews have rated this product an average of 4.6. Based on our statistical modeling, the discrepancy in average rating between these two groups is significant enough to believe that the difference is not due to random chance, and may indicate that there are unnatural reviews.

Read more about our Word Count Comparison test.

• 
• 26%
• Substantial overlapping review history

117 of the 450 reviewers have substantial overlapping product review history. These reviewers have rated this product an average of 5.0 while the reviewers who have a more unique product review history rated this product an average of 4.7. Based on our statistical modeling, the discrepancy in average rating between these two groups is significant enough to believe that the difference is not due to random chance, and may indicate that there are unnatural reviews.

Read more about our Overlapping Review History test.

• 2
• Reviews have been deleted

We discovered a total of 2 deleted Reviews for this product, with an average rating of 5. Even though deleted reviews don't affect the average rating, the fact that action was taken to delete reviews raises some red flags about the integrity of the reviews for the product as whole.

There are a few limitations to keep in mind regarding the Deleted Reviews test:

1. We don't have a magic ability to collect every single deleted review; we can only identify reviews as deleted if we collect them on one date and then notice they are no longer visible on a subsequent date.
2. We have no information on reviews that were never published in the first place.
3. We also don't know why these reviews were removed. It could be action from the platform, personal decision by the review author, part of an entire account closure, even some data error on our part, etc.

Read more about our Deleted Reviews test.

Show distribution of deleted reviews

• 
• 20%
• Created over 2 days

We counted 450 reviews for this product over the span of 21 days, an average of 21.4 reviews per day. If these reviews were created randomly, there would be a 99.9% chance that we would see 37 or fewer reviews on any given day.

However, we see the following 2 days exceeding this threshold:

• 46 Reviews on Aug 29, 2019 (Avg. rating: 4.8)
• 44 Reviews on Aug 28, 2019 (Avg. rating: 4.9)

In total, we found that 90 reviews were created on just 2 days. This is an excessively high number of reviews submitted on these high volume days.

Read more about our Rating Trend test.

One-Hit Wonders

• 
• 24%
• have only posted one review

106 of the 450 reviewers have only reviewed this product. While this is more One-Hit Wonders than we'd expect to see, it does not appear to have a significant impact on the overall rating.

Read more about our Suspicious Reviewers test.

• 
• 62%
• From reviewers with an overrepresented participation

We see the following 1 participation group with a statistically significant greater concentration than what we'd expect to see:

• Reviewers with 1-5 Reviews: 62.4% (Avg. rating: 4.7)

In total, we found that 281 reviewers (or 62%) are within an overrepresented participation group. This is an excessively high number of reviewers in overrepresented participation groups.

Read more about our Reviewer Participation test.

• 
• 5%
• Unverified Purchases

21 of the 450 total reviews for this product are unverified purchases. This is within an acceptable range and it does not appear to be significantly affecting the overall rating for this product.

Unverified purchases may be the result of Kindle Unlimited readers, buyers who didn't pay full price, or reviewers who did not purchase the product at Amazon. Read more about our Unverified Purchases test.

Brand Repeaters

We didn't detect a substantial amount of Brand Repeaters.

We have not yet completed optimization for this test for Hanzi or Kanji.

We have not yet completed optimization for this test for Hanzi or Kanji.