The Probabilities and Financial Impact of Gacha Games

Genshin Impact

Kevin Wang and Nick Zhang

Introduction

Genshin Impact is a free-to-play action role-playing game developed and published by miHoYo. The game features a fantasy open world environment and action based battle system using elemental magic, character switching and uses gacha game monetization for players to obtain new characters, weapons, and other resources. The game is online-only and features limited co-op mode, allowing up to four players to play together. It was released on September 28, 2020. About 21.3 million people registered for the game, with 17 million downlods at the games launch. Read more about Genshin Impact, and download the game for youself today: Genshin Impact

The Potential Plight of Gacha Games

Gacha games contain the gacha mechanic, similar to the capsule toy vending machine idea. Players spend in-game currency to recieve a random virtual item. Genshin Impact gacha rolls contain the following prizes: 3 Star Weapons, 4 Star Weapons, 4 Star Characters, 5 Star Weapons, and 5 Star Characters. Of course, higher the star ranking, higher the rarity of the item, and higher the appeal. Countless players have spent thousands of dollars of games such as Genshin Impact, even though it is free-to-play.

Our Objectives

We will analyze the probabilities of attaining the highest ranking items possible, as well as determining the average cost of rolling one 5 star item. Furthermore, we will test to see if there there is a strong positive relationship between money and the number of 5 star achieved, i.e the more money one spends would it lead to more 5 stars? We will then determine the financial costs of these gacha rolls and the investment into Genshin Impact for different player groups. Finally, we will calculate the financial impact of attaining one 5 Star on the typical, young adult, single-person household. Personally, since we also love playing this game, we are interested in the math and statistics behind Genshin Impact's built-in gambling system, and we hope that others will also be interested in the financial impact behind paying to have a strong team of characters in the game.

Collecting Wishes Data

Gacha rolls in Genshin Impact are called wishes. We manually simulated and recorded 500 10-item rolls using the following simulator: Wish Simulator. Go ahead, try your luck! Since our data is straightforward and manually collected to our specifications, there was no need to tidy or modify our data. We immediately processed the data from a csv into a Pandas dataframe.

With the dataframe above, let us calcuate the sum of each star rating item we rolled.

Let us visualize the odds better with a simple barplot. Spoiler, the odds are horrendous.

Now we will count and record the number of rolls between each 5 star attained and compute the average distance, based on our data above.

Fitting a Linear Model

We could use the value above to say that a player would, on average, need to roll 55 times to get a 5 star summon (weapon or character). However, we can double check by trying to fit a linear model.

We can see that the p-value assosiated with our F-statistic is extremely small (almost zero), meaning that our linear model is a good fit. Also, we can see that our predictor (index), has a P-value of zero, meaning that it is a significant predictor in explaining variability of our response variable (number of 5 star weapons / characters obtained). We can also see for simple linear regression, we have an R-squared of 0.998, meaning that the model we have just created can explain 99.8% of all variability in the model. Thus, we have determined that the number of rolls you will instigate is correlated with the amount of 5 stars obtained. Due to the high R-squared value, it is unlikely that there are additional predictors that we have not accounted for.

The slope by itself indicates that for every 1 grouping of rolls (or for every 10 rolls) the number of 5 star weapons / characters increases by 0.1421 items. Since this does not make much sense, we can instead repharse it as such:

For every 7 rolls of 10 (70 individual rolls) rolls, the number of 5 star weapons / characters increases by approximately 1.

Note: In this case, an intercept of 2.4255 does not make any sense, since that would be implying that despite doing no rolls, we would still end up with around 3 5 star items / characters. Moving forward, we will ignore the intercept due to this logical fallacy.

Analyzing Probabilties

Based on our data, let us see the probability of attaining either 5 star character or weapon, seperately.

However, we need to factor in both the sum of 5 star characters and weapons we get. Why? Each roll we are doing has the possiblity of attaining any 5 star item (or multiple if you are really lucky).

Woah! The adjusted probability of achieving a five star item is around 1.54%. We also need to take into account that Genshin Impact implements a pity system. The game takes "pity" on the player, and guarantees an item after x number of rolls. For a 5 star, the pity system kicks in at 90 rolls, i.e after 89 rolls, if you do not attain a 5 star character, the next 90th roll will be a guaranteed 5 star item. Then, the pity system resets until the next 5 star item is attained. Wow, this is quite revolutionary for the gacha game industry.

We can mathematically compute a similar probability to what we calculated above. Following a binomial probability distrubution, with probability of each roll being .006, the cummulative probability of attaining one 5 star item for 90 rolls is calculated as follows:

First we must calculate the cummulative probability of attaining one 5 star over 89 rolls:
\begin{equation} P(X < x) = F(1; .006, 89) = \sum_{i=0}^{1} \binom{89}{i}(p)^{i}(1-p)^{89-i}))= .5853 \end{equation} \begin{equation} P(X \geq x) = 1 - .585313 = .4147 \end{equation}
Factor in the 100% probability of attaining a 5 Star on the 90th roll. Then, the cummulative probaility at 90 rolls is:
\begin{equation} 1 + .4147 = 1.4147 \end{equation}
Adjusted probability per roll is:
\begin{equation} 1.4147 / 90 = .01571 \approx 1.6\% \end{equation}

So we have the adjusted probability to attain a 5 Star per roll. Now, here is the question. How many rolls do we expected to perform in to order to attain that 5 Star item. This follows a geometric probability distribution, specifically the distribution of the number x of Bernoulli trials needed to get one success.The expected value of rolls to attain 1 success is: \begin{equation} E(rolls) = 1/ p \end{equation} Let us calculate the expected number of rolls based on non-pity system probability. \begin{equation} E(rolls) = 1/(.006) \approx 167 \;rolls \end{equation} Now, let us calculate the expected number of rolls based on the pity system probability. \begin{equation} E(rolls) = 1/(.016) \approx 63 \;rolls \end{equation} That is about 100 rolls less, saving countless dollars. The financial horror will be showcased later.

Let us graph the geometric distribution with probability = 0.016 and analyze the cummulative probabilities. Read more about geometric probability distributions here: Geometric Distribution

From the CDF values, one would only have a 50% change of attaining a 5 star by the 44th roll. Our cummulative probabilities doesn't even reach 80% to 90% by the 80th to 89th roll.

Costs of Rolls

Primogems are the special currency in game that rolls are bought with. Each roll costs 160 primogems. The unit cost of primogems is around 0.0157 USD. Let's do some simple roll costs, based on our three numbers of rolls computed previously:

\begin{equation} Each\ roll\ will\ cost = (0.0157 * 160) \approx $2.51 \end{equation}\begin{equation} Our\ simulation\ had\ an\ average\ of\ 55\ rolls\ per\ 5\ star\ item = ($2.51 * 55) \approx $138.16 \end{equation}\begin{equation} Our\ computed\ expected\ value\ was\ 63\ rolls = ($2.51 * 63) \approx $158.13 \end{equation}\begin{equation} Our\ linear\ model\ predicted\ 70\ rolls\ per\ 5\ star\ item = ($2.51 * 70) \approx $175.70 \end{equation}

So, we have a range of potential (Values could exceed or be below this range) costs from 138.16 to 175.70 USD just to attain one 5 star item.

Potential Yearly Primogem Gain Amongst Players

Now, we will speculate how many primogems a certain player may accumulate over the course of a non-leap year (365 days). This will be related to the number of 5 star characters that sum may attain, as well as the potential cost of those primogems if one buys them outright. To calculate potential costs, we need to calculate how many primogems players may obtain in a standard year. Their activties and respective primogem gains are detailed below:

We have grouped players into four general categories: Casual Free to Play, Hardcore Free to Play, Casual Whale, and Hardcore Whale. Each category of players will have specific actions and purchases they may take. Two main subgroups exists:

Casual Free to Play

The Casual F2P may pursue the following actities:

To best capture how the casual F2P may play, we will run a randomize function on the values above, since a casual player may not work towards attaining the max primogems possible. We will simulate this 10,000 times and take the average to attain a more precise sum.

Hardcore Free to Play

The Hardcore F2P may pursue the following actities:

To best capture how the Hardcore F2P may play, we will run a randomize function on some the values above, since even a hardcore free-to-play may not work towards, or even be able to attain the max primogems possible. We will simulate this 10,000 times and take the average to attain a more precise sum.

Casual Whales

The Casual Whale may pursue the following actities:

To best capture how the Casual Whales may play, we will run a randomize function on some the values above, since a casual whale may not work towards attaining the max primogems possible. We will simulate this 10,000 times and take the average to attain a more precise sum.

Hardcore Whales

The Hardcore Whale may pursue the following actities:

Hardcore Whales will attain everything possible from these sources.

Primogems, Rolls, Costs: Got to Catch Them All?

To summarize, here are the potential year sum for each category of player:

About how many rolls do theses values covert to?

How many 5 Star Items can this translate into? We will use our simulated average of 55 rolls per 5 star as a upper bound, and our linear model's predicted 70 rolls per 5 star as a lower bound.

Based the calculations above, even for whales, it takes about a year to attain not even all of the 5 star characters guranteed. Thus, it is often the case whales would not only buy the battle pass and monthly pass, but they have a chance of purchasing additional primogems seperately. Note the unit cost of a primo gem is 0.0154 USD.

We will compute a new set of values that captures, only in lucky sernarios, the amount of money whales may spend on obtaining a certain number or certain selection of 5 star characters.

Casual Whales

\begin{equation} E(times) = 1/ p \end{equation}\begin{equation} E(times) = 1/(1/9) \approx 9 \;times \end{equation}

This means that I expected to roll 9 5 Star Character until one obtains the character he/she wants. Since the expected number of rolls per 5 star was computed to be 63, we can calculate the costs as follows:

Hardcore Whales

This is a disturbance in the Force. Potentially, a whale may spend thousands of dollars on Genshin Impact, a Free to Play game, in one or more sittings, not throughout the year. It is important to note that it is not guarenteed to attain a unique 5 star character every time you attain a 5 star; there are repeats. Furthermore, whales may not be finished after attaining all 9 characters, for they can use to repeated 5 star character drops to level up those respective drops, for a total of 6 times. A player may go for 6 drops per 9 5 star character (54 times).

These...calculations may seem like speculation; who would rationally spend this amount of money? It seems that there are people who do:

Mtashed's $2000 Genshin Impact Blowout

Tectone Spends more than $5000 on Genshin Impact

Most likely, these are not the only examples. Otherwise, how else could Genshin Impact generate $400 Million Dollars?

Potential Economic Impact

Given that we have now calculated how much money on average would be needed for each target demographic, now lets see how much pursuing any one of those paths will impact someone's economic position. For this section, we used data gathered from the 2018 - 2019 US census on median income, and compared them to the values calculated above.

Source: https://www.census.gov/library/publications/2020/demo/p60-270.html#:~:text=Median%20household%20income%20was%20%2468%2C703,and%20Table%20A%2D1).

This table, once cleaned up, still has a lot of data. However, we want to observe a couple demographics for our analysis.

First off, age should definetely be something to look at, because Genshin Impact, and video games in general, has a greater appeal to children, people in their teens, and young adults. For this reason, we look at age range 15 - 24 and age range 24 - 35, since those ranges best describe the age of the players of Genshin Impact

Next, we should consider the familial situation of each player. We do this by looking at married and unmarried males, and married and unmaried females.

Finally, we decided to partition the country of America into different regions - Northeast, Midwest, Southwest, and West. This is because the socioeconomic conditions in America vary greatly depending on what region you live in; for example, there is more money councentrated in the Northeast and West than there is in the Midwest, which is still very agrarian, and the Southwest, which does not have as many economic centers of commerce or business.

Using these 10 subdivisions, we created pie charts based on all those demographics' median incomes, where we counted how much of their total median income would be spent on the game depending on their playstyle (casual whale or hardcore whale). The values of potential expenditure on this game were speculated above.

Below is the function we used to create the pie graphs, where classification is a string that determines which spending habit we want to measure against our chosen demographics:

Casual Whale (Speculated to Spend: 1546.878 USD)

Based on the graphs above, we can see the amount of money spent on Genshin Impact (Blue) is only a small part of each group's expected income. Percentage of money spent on the game is still around 2% to 5% of someone's total income, which, while not a staggering amount, is still a mildly large amount to spend on a single pasttime. It is also worth noting that by a report filed by the US Bureau of Labor, the average percentage of annual income spent on entertainment should average out to be 3% of someone's total annual income.

Source: https://www.bls.gov/news.release/cesan.nr0.htm

Hardcore Whale (Speculated to Spend: 12813.582 USD)

Based on the graphs above, we can see the amount of money spent on Genshin Impact (Blue) is a much larger portion of someone's expected income. It is with these graphs that we can really analyze how destructive this type of spending could be. With a range of 18% to as high as 39% of someone's annual income, this is a significant amount of money to spend on a video game. We can also see some more pronounced differences on how this would affect you:

Nevertheless, all these values are much higher than what the average household may spend on entertainment.

Fin

Our objectives were to analyze the probabilities of attaining 5 star items and studying the costs of attempting to do so. Our research, though heavy with speculation and assumptions, is based in statistical analysis and logical reasoning. All summon and cost data were pulled directly from the game and simulators that were created with true Genshin Impact probabilites and math. We used data modeling techniques to help visualize your odds as well as the potential economic impact of spending money.

We hope that by analyzing the monetary costs of gambling in Genshin Impact may persuade people be cautious in how much money they spend. The game is free-to-play, and the company behind it invested heavily into making a fully devoloped, open world game with deep and intriguing lore. Players may choose to spend some money to buy the monthly pass or other packages to help support the company. However, it is a gacha game, and those with gambling addictions should be wary of what they may be spending for. The game can be played totally without spending a single dollar, and none of the 5 star characters are game breaking or changing.

There are plenty more ways to analyze economic costs of Genshin Impact. Instead of money, one could study the cost of time spent. What could be the opportunity cost of spending hours on this addicting game? Of course that research is difficult, for data may be hard to find, and the interpretation and analysis of that data would be mostly speculative. It would have been interesting though to ponder about.

I hope our speculative yet statistical analysis was fun to explore. We highly recommend this game, for the world, characters, lore, gameplay mechanics, and the community you can be immersed in is well worth your time, and best of all its free to play! Hope you have fun with Genshin Impact traveler - we sure did!