How many and what percentage of Yelp users mainly write reviews for restaurants?

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How many and what percentage of Yelp users mainly write reviews for restaurants?

Hello! Thank you for your request to determine how many and what percentage of Yelp users mainly write reviews for restaurants. The short version is that of the 127 million reviews posted to Yelp since 2004, 36% of these have been for restaurants. An estimated 4.46 million Yelp users have posted reviews about restaurants. An estimated 0.67% of all Yelp users post reviews about restaurants. An estimated 1.87% of Yelp users post reviews. The average restaurant reviewer on Yelp posts approximately 10.24 reviews. Below you will find a deep-dive of my findings.

METHODOLOGY
First, I searched for any sources that stated the requested information directly. After no such source could be found, I endeavored to search for any metrics that could be used to estimate these values to a statistically viable certainty. The metrics used in estimating these numbers included: daily unique users, number of reviews per user, percentage of reviews that are about restaurants, and the average amount of reviews by reviewer.

It should be noted that the 2016 Annual Form 10-K report from the United States Securities and Exchange Commission states that there have been several Yelp reviews that have been removed, or made unavailable. This, however, is irrelevant since the users had initially posted these reviews, regardless of whether these reviews are still visible or not. The charts provided in this report are stated to include all reviewed businesses and number of reviews, regardless of whether or not these reviews are still visible on the platform.

Please note that the information required was not directly stated in any source consulted, however enough information was available to estimate the numbers to a statistical certainty.

TOTAL NUMBER OF YELP USERS THAT REVIEW RESTAURANTS
According to a 2017 Fact sheet released by Yelp, there have been 127 million reviews posted on this platform since its inception in 2004. This fact sheet goes on to state that 18% of all businesses reviewed have been restaurants. 

However, the company's Form 10-K report states that 36% of all reviews (including those that have not been recommended or have been removed) are for restaurants.  This would indicate that the same restaurant receives multiple reviews.  Based on this figure, the number of restaurant reviews on Yelp is estimated as follows:

127M*0.36 = an estimated 45.72 million restaurant reviews on Yelp, to date. Furthermore, a study, performed by Research Gate, states that restaurant reviewers on Yelp post on average 10.24 reviews. This would indicate that:

45.72M/10.24 = an estimated 4.46 million users have reviewed restaurants on Yelp.

PERCENTAGE OF YELP USERS THAT REVIEW RESTAURANTS
Data provided by Statista (a trusted market reporting platform) states that in 2016 there were 25.81 million reviews posted to Yelp (121.02 - 95.21).

According to data provided by Quantcast (a web analytics platform which showcases statistics about online engagement of various platforms) the average number of unique Yelp users, every 30 days in 2016, amounted to the following, by month:

(102.0M + 101.9M + 104.7M + 110.8M + 114.2M + 120.5M + 118.2M + 117.2M + 117.1M + 118.0M + 118.9M + 118.5M)/12 months = an estimated average of 113.5 million unique visitors every 30 days in 2016. This would then amount to:

113.5M/30 = an estimated 3.78 million unique users per day in 2016.

From the Statista data, we see:
25,810,000 (annual number of reviews)/365 = an estimated average of 70,712.33 reviews posted to Yelp each day.

However, it is still likely that a reviewer could post multiple reviews per day. A report on Techcrunch states that the average Yelp user spends approximately 3.3 minutes on Yelp per visit. Although this report is from 2009, it is entirely feasible that the time spent on this platform will remain relatively similar, or increase with time.  Therefore if we break the above mentioned data-points down by the minute (so as to eliminate the possibility of multiple reviews by a single user), we see:

70,712.33/24 hours per day /60 minutes per hour = an estimated average of 49.11 reviews per minute on Yelp in 2016.

If we apply the 36% of reviews that are for restaurants, we see: 
49.11*0.36 = an estimated average of 17.68 restaurant reviews posted to Yelp every minute in 2016.

If we now do the same for daily users, we see:
3,780,000/24 hours per day/60 minutes per hour = an estimated 2,625 unique visitors on Yelp every minute in 2016.

If we now combine these data points, we can estimate that:
(17.68/2,625) * 100 = an estimated 0.67% of Yelp users posted reviews about restaurants in 2016.

ALIGNING FINDINGS WITH THE 1/9/90 RULE
As mentioned in the original response to this question, the 1/9/90 rule is a marketing strategy used by social media platforms in assessing engagement and contribution. This rule states that 1% of users will create content, 9% will comment and share this content and 90% will merely view the content that has been created by the 1%. The only mention that Yelp operates under the 1/9/10 rule is in a blog post, written by Susan Kuchinsas, whereby she references an article from 2011, and mentions that Luther Lowe, manager of business outreach at Yelp, cited the 1/9/90 rule.  However, there was no statistical data provided on the subject.

If we assess the estimations derived from the data provided by Quantcast with that derived from the data provided by Statista, we see:
49.11 (estimated number of restaurant reviews per minute) /2,625 (estimated number of unique visitors per minute) * 100 = an estimated 1.87% of Yelp users post reviews. This would suggest that Yelp has a far more active audience than the 1/9/90 benchmark would suggest.

CONCLUSION
To wrap it up, of the 127 million reviews posted to Yelp since 2004, 36% of these have been for restaurants. An estimated 4.46 million Yelp users have posted reviews about restaurants. An estimated 0.67% of Yelp users post reviews about restaurants. An estimated 1.87% of Yelp users post reviews. The average restaurant reviewer on Yelp posts approximately 10.24 reviews.

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