How important is
service to different categories of restaurants in NYC? To address this, I used
Yelp comment data (as of Nov 6th, 2014) from the top 40 restaurants from different categories of cuisine (e.g. Traditional American, French, Mexican, burgers, etc.). I looked at high (5-star) and low (1-star) comments in order to discover the relative impact of positive and negative service in restaurant assessments.
To calculate the importance of
service, I used a text mining method called term frequency inverse document frequency (
tf-idf), which counts the number of times a word appears in all the comments and divides that number by the number of comments that contain at least one instance of that word. This calculation allows us to quantify the importance of words while reducing the importance of words that appear in almost all comments such as 'a', 'the', 'I', etc. that are less meaningful. Once I found the tf-idf values of all the words, I normalized the tf-idf value of the word
service relative to the highest tf-idf value (associated with the most important word) to obtain a measure for the relative importance of
service in the users' dining experiences. For example, if the highest tf-idf was 0.5 and
service's tf-idf value was 0.2,
service's normalized tf-idf would be 0.4 or 40%.
Figures 1 and 2 below are some example
word clouds that illustrate the relative importance (i.e. relative tf-idf) of the word
service. More specifically, each word cloud below shows the top 50 tf-idf words from positive (Figure 1) and negative (Figure 2) comments in a particular restaurant category, and sizes the words by its relative tf-idf value.
Figure 1
 |
French Restaurant Category Word Cloud (Positive 5-Star Comments)
Relatively High Service Importance |
Figure 2
 |
Pizza Restaurant Category Word Cloud (Negative 1-Star Comments)
Relatively Low Service Importance |
High Yelp Ratings
Using only 5-star rated comments from the different categories of restaurants, I found the following (Figure 3) relative tf-idf values for the word service ordered by restaurant category from highest to lowest.
Figure 3
The categories with the most positive service comments were French, seafood, steak, and Italian restaurants. The restaurant categories with the least positive service comments (note that this does not mean negative, simply less impact of service) were food courts, food stands, pizza, and hot dog.
Low Yelp Ratings
Using only 1-star rated comments from the different categories of restaurants, I found the following (Figure 4) relative tf-idf values for the word service ordered by restaurant category from highest to lowest.
Figure 4
The categories with the most negative service comments were traditional American, French, German, and fondue restaurants. The restaurant categories with the least negative service comments were food courts, food stands, pizza, and hot dog.
From Figures 3 and 4, the importance of service appears to be similar regardless of the valence of the comments for a particular restaurant category. Statistically, a positive relationship was indeed found between high and low service normalized tf-idf values (p<0.001). Simply put, NYC diners within a restaurant category placed roughly equal importance to service no matter if it was a positive or negative experience. But why would this be the case? One possibility is that the price of the restaurant influenced how important service was for the diners. To examine this possibility, I used Yelp's restaurant pricing system ($, $$, $$$, $$$$). These dollar signs represent the cost per person for a meal including one drink, tax, and tip.
- $ = under $10
- $$ = $11-$30
- $$$ = $31-$60
- $$$$ = above $61
For each category of food, I calculated a PRICE SCORE to quantify the overall price of a particular restaurant category from its top 40 restaurants using the following equation:
PRICE SCORE =
(# of $ restaurants) + 2*(# of $$ restaurants) + 3*(# of $$$ restaurants) + 4*(# of $$$$ restaurants)
As one may expect, I found a significant (p=0.001) positive correlation between price score and positive service importance (from 5-star Yelp comments). This means the more expensive the restaurant category, the better the service and/or the more importance Yelp diners placed on good service in their reviews. Although a negative correlation was found between price score and negative service importance (from 1-star Yelp comments), this correlation was not significant (p=0.158).
Ultimately for diners in the Big Apple, the more you pay for your meal, the better the service and/or the more attention you pay to great service. In addition, you also pay more attention to bad service.
Do LA restaurants generally offer better service than NYC restaurants? As before, I answered this question using Yelp restaurant comments from the top 40 restaurants from 44 different categories of cuisine in LA and NYC. To determine the relative impact of service, I first calculated the tf-idf of the word service in all comments from the top 40 restaurants in each of the 44 categories. I then normalized the tf-idf of the word service as a percentage in relation to the highest tf-idf word from the same set of comments. I only used 5-star and 1-star Yelp comments to remove any ambiguity in sentiment when comparing positive and negative service, respectively. I then compared the average impact of positive and negative service across all 44 restaurant categories within each city as well as between cities. 
