Tuesday, August 21, 2012

Showcase Showdown Analysis: Circular Reasoning and Oscillating Nash Equilibrium

The Showcase Showdown is a portion of the game-show The Price Is Right, in which the contestants spin the Big Wheel that has 20 sections randomly distributed, from 5 cents to $1.00 in 5-cent increments. The objective is to get as close to $1.00 as possible without going over, with one initial spin and an optional second spin. In the game, three contestants play the game to determine who has the highest value. What's the strategy in this game for the first contestant? An intuitive response may be to spin again for 50 or less on the first spin; keep the first spin if it's 55 or greater. Unfortunately, it's not as simple as that.

One strategy would be to spin the wheel the second time, only if the first spin resulted in less than the expected total outcome from the game, conditional to the outcome from the first spin. We can analyze the extreme discrete cases first to get a better understanding. If the first spin is 100, all second spins will make the total go over, resulting in total score of 0. In that case, the contestant will definitely keep the first spin of 100. On the other extreme, the expected total from the two spins, conditional to the first being 5, is 52.25. In that case, taking the second spin is better off. Here is the complete table, with the higher result reflecting the course of action pursued:

First Spin 2 Spins Avg Total Higher Result
5 52.25 52.25
10 51.75 51.75
15 51 51
20 50 50
25 48.75 48.75
30 47.25 47.25
35 45.5 45.5
40 43.5 43.5
45 41.25 45
50 38.75 50
55 36 55
60 33 60
65 29.75 65
70 26.25 70
75 22.5 75
80 18.5 80
85 14.25 85
90 9.75 90
95 5 95
100 0 100

If the first spin were 40 or less, having a second spin will on average produce a better result. The average of the third column gives the expected result from the game: 63. However, there is one hole in this reasoning when applied to the game. This would work perfectly fine if the first contestant played the game for himself or herself, only concerned about maximizing the individual score given the risk-reward offset. Instead, of the three contestants, only the one with the highest result wins. If the first contestant got anything from 45 to 60, inclusive on the first spin, it would've been strategically better to keep it in the aforementioned reasoning. However, since the objective is to beat all other contestants, rather than maximizing individual scores, at that point of the game it may be more reasonable to spin again nevertheless.

This is where the circular reasoning kicks in. If the contestant's decision is to spin the wheel the second time if the first spin were less than 63, then the total expected value drops to 59.95. Essentially, while the contestant tries to base the individual decision given the overall expected result, the overall expected results depend exactly on the individual contestants' decision. It's a circular route of logic, and also illustrates game theory being applied. Having 40 and 45 be the cutoff would the best risk-reward optimization decision on the individual level. However when that is the baseline, the dominant strategy is then to use 63 as the decision's critical point. When players do that, they all incur more risk and distort the overall expected result downward. Would contestant then use 59.95 as the decision's critical point?

If the contestants did, the next critical point would be 61.3. Here, if 61.3 were the next critical point, it forces 59.95 to again be the overall expected value, just like 63 did. Therefore, the "Nash equilibrium" is a perpetual oscillation between 59.95 and 61.3. In the end, the only definitely conclusions are to spin again if the first spin is 40 or lower, and to keep the first spin if it's 65 or greater. Having 45 and 50 as the first spin stands in the grey area, and 60 is dead in no man's land, caught in between the oscillating equilibrium.

Saturday, August 4, 2012

Evaluating Cleveland RTA Park-and-Ride Locations

See previous related post: 10PM, Tower City Terminal

Having convenient and pleasant park-and-ride rail stations is the key to developing effective public transportation systems that reach out to those in the suburbs. In Cleveland, many stations come with free parking along the rail lines. Park-and-ride can save two types of costs: a fixed cost of parking, and the variable cost of driving, which includes gasoline and depreciation. Merely accounting for parking, even for two people park-and-ride is a cost-effective alternative ($9 round-trip) to most  parking garage rates downtown, particularly on event nights. However, the system doesn't serve all regions of the metropolitan area evenly.

Bypassing Downtown
If one is to stop at downtown but ultimately bypass it on the overall route, East 55th Street Rapid Station strategically has the best location for park-and-ride. It is located right off the junction of I-490 and I-77, offering quick access back onto the highway. Furthermore, all three (Blue, Green, Red) Lines go from E. 55th to Tower City, minimizing the expected wait-time to catch any of the trains. This quick stretch of 7 minutes is particularly unique in that heavy-rail (Red) and light-rail (Blue & Green) lines run side-by-side. Despite these advantages and its recent renovation completed in 2011, E. 55th Station does offer several important challenges. The parking lot is quite small, capable of holding fewer than 50 cars. The bigger challenge is the fact that maybe it's too close to downtown, with its inner-city location potentially deterring suburban riders who prefer stations in areas they may be more familiar with. Adding onto the problem, coming off I-490, the parking lot is not easily accessible. Bower Ave, which has direct access to the main lot on the eastern side of E. 55th, is restricted one-way lane. The easiest lot to get into is located across the street. Crossing the busy street requires a bit of walking to and waiting at the street lights.

From East Side
For those coming from the Southeast, the terminus of either Blue or Green Lines offer that opportunity. While both lines take around the same time getting to Tower City (approx. 30 min), and around the same distance to I-271, Green Line holds a slight advantage. The terminus of Blue Line, Warrensville, does not offer direct parking. Riders have to park at the adjacent Farnsleigh station. This would be fine, except that upon getting out of the lot onto Van Aken Blvd, drivers can only turn westbound. As a result, leaving the station is more burdensome than the terminus at Green Road. From the Northeast, only two stations: Superior and Windermere along the Red Line, both in East Cleveland, offer park-and-ride. Windermere Station, however, is over 2 miles off I-90 through East Cleveland. As a result, options are more sparse for those coming from the Northeast.

From West Side
Despite Red Line being the sole rail system west of Cuyahoga River, the West Side has more convenient choices. Every station from Brookpark to West Blvd has free parking exceeding 100 spaces, and the choice of station depends on whether one is predominantly coming along the direction of I-90 or I-480. Brookpark is conveniently located near the junction I-71 and I-480, offering the best alternative for those coming from the Southwest. From the Northwest, Triskett and W. 117th Stations are convenient due to their proximity to I-90, along the Cleveland-Lakewood border, and these stations are only around 15 min away from Tower City.

South?
With Lake Erie off to the north of the city, the RTA system currently leaves the South devoid of rail connection. For those predominantly coming from the direction of I-77, there is not an effective park-and-ride location. E. 55th would be the natural choice from the map, but given the reasons described above, may not be the ideal choice. Plus, going up to I-490 is almost going into downtown anyways; barely any money is saved on the gas. The RTA does have several Park-N-Ride routes using express buses. They originate from southern suburbs like Parma and Brecksville, but these programs only operate on weekdays, during rush-hours, and only in the rush-hour direction. As a result, they are not viable for night or weekend events. The current system favors West (whether Northwest from I-90 or Southwest from I-480) and Southeast the most, while Northeast and particularly the South don't get nearly as much benefit.

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Thursday, August 2, 2012

Olympics Basketball Record

Team USA was the heavy favorites to win the Men's Basketball tournament, and today it went onto making records in its Nigeria 156-73 win against Nigeria. What's more impressive about the score, particularly putting it into perspectives for American fans used to the NBA style, is that the Olympics games are only 40 minutes long in regulation, as opposed to the 48 in NBA. Keeping the constant ratio, the 156 points would've translated to 156 / 40 * 48 = 187.2 points over a 48-minute period.

The NBA record for the most number of points in one game is 186, scored by Detroit against Denver in 1983. Furthermore, that game went into the third overtime period. Detroit won 186-184, as the teams combined for 370 points, another NBA record. The margin of victory from today's game (83) also shattered the NBA record of 68. The NBA record for the fewest number of points in a game of the modern era is 49, recorded by Chicago in 1999. That is nearly only a quarter of (specific factor difference of 3.82) the number of points Team USA scored today, by using the projected score over 48 minutes.

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