Monday, February 25, 2008

How sulit is sulit: A quantitative approach

Sulit, or value for money, is a concept we often use when reviewing restaurants. Basically, it is the difference between the value of a meal (i.e., how satisfied we are with the experience) and the price we actually paid for it. By definition, sulit is a subjective measure since we are comparing something subjective (value) with something objective (price). In this post, I will present my subjective quantitative measurement of value, which I will then use for subsequent reviews.

First, let us identify my five criteria for measuring restaurants:

Quality (Q)-- refers to the quality, freshness, and authenticity of the ingredients used in the dish. Presentation, cleanliness, and temperature of the dish are also considered in this scale.

Taste (T)-- refers to the overall taste and texture of the food.

Quantity (W)-- refers to the serving size of the dish.

Service (S)-- refers to the attentiveness, friendliness, and efficiency of all crew who have contact with customers. Their attention to detail and management of complaints (if any) are also considered.

Ambience (A)-- refers to the overall quality of the restaurant's physical space. Considered here are ambience (of course), cleanliness, facilities, and even parking availability.

All scales are rated from 1 (very bad) to 10 (perfect) with 5 as barely acceptable. For criteria Q, T, and W, if more than one dish was sampled (which is often the case), the rating will reflect the average rating for the dishes. Value (V), which is our main interest, is expressed in peso terms and is a function of the five criteria with the form
V = (QTWSA)^(2/3).

The result of V(.) is my subjective valuation of the meal in current pesos, so it represents the maximum I am willing to pay per person for a meal in the restaurant given their scores in Q, T, W, S, and A. Thus, for a perfect restaurant that scores 10 in all criteria, I am willing to pay P2,154.43 per person for a meal. On the other hand, a restaurant that scores 5 in all criteria (just enough not to piss me off and still walk away with a smile) is worth P213.75 per person at most.

Sulit (S), then, is defined as S = V/P where P is the actual price per person for a meal. If S is greater than one, the restaurant is considered sulit; less than one it is not sulit; equal to one it is neutral.

WARNING: Technical Content (apologies to Mythbusters)

Any student of Economics will recognise the form of V(.) as a Cobb-Douglas utility function (homogeneous of degree 10/3). In this case, however, I am taking liberties with the definition of utility and I'm attaching a peso value to the utility measure (i.e., one unit if utility is equivalent to one peso). To illustrate, consider the following graph in Q-W space (forget about T, S, and A for now since I can't draw in five dimensions):

The 45-degree line from the origin represents increasing price and value given in pesos. Now consider the blue curve: each point in the curve represents different values for Q and W that yield the same V; the curve crosses the 45-degree line at only one point so the peso value is unique. Thus, restaurant A, with its low quality but big serving size, can have the same value as restaurant B, which has high quality but a small serving size. Restaurant C, however, being on a lower curve, has a lower value than restaurants A and B.

Suppose now that restaurants A, B, and C charge a per-person price of D pesos. A and B would then be considered as sulit restaurants while C would not.

To illustrate, consider some restaurant K which I rate as follows: Q = 7, W = 6, T = 4, S = 7, A = 7. Thus, we get V = P407.70. However, you can expect to spend around P500/person for a meal and a drink in restaurant K. It therefore registers S = 0.82 < 1, so it is not sulit.


lateralus said...

there should be at least five people testing the food to make the numbers more reliable. The equation can have dramatic fluctuations due to changes to just one or two variables.

E. Cross Saltire said...

I agree-- increasing the sample size (and getting the average before plugging into V) will decrease the degree of subjectivity of the measure. Unfortunately, rarely do I dine with five foodies willing to use the scale.

Nice food blog, btw. I'll add you to my links.