In AMC’s The Walking Dead, former sheriff’s deputy Rick Grimes awakens from a coma and finds himself in what must surely seem at first to be a nightmare. Highways are littered with abandoned vehicles, towns and cities are deserted, and the entire world is overrun with flesh-eating zombies called “walkers.”
In the wake of civilization’s destruction, Rick and his son Carl must now band together with any other humans they can find who might be able to help them survive. And as the series progresses (Season 5 concluded this past March), it becomes evident that the most dangerous threat to Rick and his group might not be walkers at all, but rather fellow survivors such as themselves.
Based on a comic book series of the same name, The Walking Dead is not only wildly popular, (averaging 14.4 million viewers per episode during the fifth and most recent season), but also notoriously unpredictable and stressful to watch.
As with other critically acclaimed series, such as HBO’s Game of Thrones, the writers for The Walking Dead seem to relish killing off major characters without warning.
(It took me a week to work up enough courage to finally watch the Season 5 finale.)
So in an attempt to figure out when my favorite characters might eventually become walker food, I gathered some data and conducted a formal survival analysis to try to estimate the probability of characters’ survival from one episode to the next.
Although my analysis obviously won’t be able to answer questions about when specific individual characters will die (that will ultimately be up to the writers and producers of the show, after all), it might help in deciding how attached you should get to any new characters that crop up in Season 6.
For every character that has appeared so far in the series (a total of 67 episodes), I compiled the following information from The Walking Dead Wiki:
- Character Name
- Status (i.e., alive, dead, or unknown)
- Number of episodes through which the character lived (Note: This is not necessarily the same as the number of episodes in which the character actually appeared)
*Data pertains only to episodes aired on TV. Events and characters depicted in comics, video games, and webisodes are thereby excluded from this analysis.
Character Status: Who is alive and who is dead (No Spoilers)?
From the beginning of Season 1 to the end of Season 5, there have been a total of 194 characters on The Walking Dead (excluding non-human animals, such as horses and dogs, as well as artificial forms of intelligence, such as the computer in charge of operating the Center for Disease Control building in Season 1).
Out of all the characters that have so far appeared on the show, 34 (18%) are still alive, 136 (70%) are dead, and 24 (12%) have an unknown status.
132 (68%) of the characters have been male, and 62 (32%) have been female.
Moreover, 138 of the characters have been Caucasian-American, 30 have been African-American, 17 have been Hispanic-American, 3 have been Asian-American, 4 have been Caucasian-Irish, 1 has been Italian-American, and 1 has been Indian-American (see Figure 1 for percentages).
Figure 1: Distribution of Walking Dead characters across racial/ethnic categories (n=194).
Among the 136 characters who died at some point during the first five seasons, 95 (70%) were male and 41 (30%) were female.
Meanwhile, 107 (79%) were White (Caucasian-American, Caucasian-Irish, or Italian-American) and 29 (21%) were of another race/ethnicity (African-American, Asian-American, Hispanic-American, or Indian-American).
Survival Analysis: What’s the probability of surviving the zombie apocalypse?
Figure 2 below shows the distribution of survival times for the 136 characters who eventually met their demise sometime during the first five seasons of the series.
The x axis shows the number of episodes through which a character could have potentially lived, and the y axis shows the percentage of characters who died during each interval of time (e.g., 0 – 5.9 episodes, 6 – 11.9 episodes, etc.).
Figure 2: Estimated Probability Density Function showing distribution of survival times for characters who ultimately died sometime during the first five seasons of The Walking Dead (n=136).
As you can see in Figure 2, most characters who die on The Walking Dead do so very soon after their initial appearance on the show.
Among the 136 characters who died sometime during the first five seasons of the series, 75% survived only up to 8 episodes. Meanwhile, 50% survived only up to 3 episodes, and 25% survived no full episodes, having died in the same episode as the one in which they made their initial appearance.
Figure 3 below shows the estimated survival function for all characters, which depicts the probability of survival beyond various points in time since a character’s initial appearance on the show.
Figure 3: Estimated Survival Function for all characters on The Walking Dead, showing probability of survival beyond x number of episodes since initial appearance on the show.
*The blue-shaded area around the survival curve represents the 95% confidence band, here Hall-Wellner confidence bands. The confidence band does not exceed 51 episodes because this is the longest stretch of time survived by a character who ultimately died.
Table 1 below provides some key points from the above survival function and shows the probability of a character’s survival up to a given number of episodes:
Table 1: Probability of a character surviving up to a given number of episodes after their initial appearance on screen; Derived from the estimated survival function shown in Figure 3.
As you can tell from Table 1, an average character’s chances of prolonged survival are generally not good.
The probability of a character surviving up to 5 episodes is essentially a coin toss, at 52.22%. And the probability of a character surviving the duration of an entire season (16 episodes) is around only 25-29%.
Analysis of Gender and Race/Ethnicity: Who is most at risk of dying?
Male vs. Female Characters
Figure 4 shows the estimated survival functions for male and female characters.
Figure 4: Estimated survival functions for male (n=132) and female characters (n=62) from The Walking Dead.
Even though there have been many more male than female characters featured on the show (132 male vs. 62 female), the probability of survival is fairly similar for each. To the extent that the two groups do in fact differ, male characters have a slightly worse survival outcome than female characters.
As a point of comparison, the probability of a female character surviving up to one episode is 85.48%, compared to only 78.79% for a male character.
We can also use Bayes’ Theorem to calculate the overall probability of death given that a character is male or female.
When we apply Bayes’ Theorem to calculate these conditional probabilities, we find that the overall probability of death given that a character is male is 71.97%, whereas the probability of death given that a character is female is only 66.13%.
White vs. Other Racial/Ethnic Groups
Figure 5 shows the estimated survival functions for white characters and characters of other races (e.g., African-American, Asian-American, Hispanic-American, and Indian-American).
Figure 5: Estimated survival functions for white characters and characters of various other races and ethnicities from The Walking Dead.
Compared to the difference in survival outcome between male and female characters, the difference between white characters and characters of other races is fairly large.
As you can see in the figure above, white characters are much more likely to die than other characters.
Consider a couple points of comparison.
The probability of a white character surviving up to one episode is 79.02%, compared to 86.26% for a character of another race. Furthermore, the probability of a white character surviving up to 20 episodes is a mere 17.03%, compared to 38.86% for a character of another race.
As with the previous analysis of gender, we can again apply Bayes Theorem to estimate the overall probability of death given that a character is white or another race. Doing so reveals that the probability of death given that a character is white is 74.83%, whereas the probability of death given that a character is another race is only 56.86%.
So when it comes to surviving the zombie apocalypse, male characters are worse off than female characters and white characters are worse off than characters of other races. And as you might expect, this means that white male characters are most likely to die, whereas non-white female characters are least likely to die.
Applying Bayes Theorem one final time reveals the following about how each group of characters generally fares:
Probability of death given that a character is white and male = 77.17%
Probability of death given that a character is white and female = 70.59%
Probability of death given that a character is non-white and male = 60.00%
Probability of death given that a character is non-white and female = 45.45%
Analysis of Hazard Rate: At what point following their initial appearance on the show is a character from The Walking Dead most at risk of dying?
Finally, Figure 6 shows the estimated hazard function for all characters from The Walking Dead.
In the context of this analysis, the hazard function describes the relative likelihood of death occurring each episode following a character’s first appearance on the show (and conditional on the character’s survival up to each episode).
Figure 6: Estimated Hazard Rate for all characters from The Walking Dead, showing a character’s relative risk of dying each episode following their initial appearance on the show (conditional on survival up to that point).
As we would expect from the data shown in Figures 2 and 3, the hazard rate is highest soon after a character makes his/her initial appearance on the series. Indeed, the hazard rate associated with a character’s first episode (EpLived = 0) is about five times larger than the hazard rate associated with a character’s tenth episode, and about 25 times larger than the hazard rate associated with a character’s 27th episode.
Interestingly, however, a character is by no means out of the woods after surviving a set number of episodes.
As you can see in Figure 6, there are two points at which the hazard rate creeps up following a relative low…like a walker sneaking up from behind.
Although risk of death decreases substantially after a character has survived one or two episodes, risk of death increases again when a character has lived for about 19 episodes, and then again when he/she has lived about 33 episodes (the increase in the hazard rate between 40 and 50 episodes should probably not be trusted, as this is likely due to the few characters who remain at risk at this point).
Conclusion: The Analyzed Dead
So what should we take from all this?
First, when it comes to survival on The Walking Dead, it’s best to be a non-white female (overall probability of death = 45.45%) and worst to be a white male (probability of death = 77.17%). So perhaps it’s not a great idea to get too attached to any new white male characters that appear on the show (*cough* Aaron & Eric *cough*).
Second, risk of death decreases substantially following a character’s survival of more than five or six episodes, but increases again when he/she has been around for roughly the equivalent of a full 16-episode season. And if a character survives beyond 16-20 episodes, they are relatively safe once again for another season.
Of course, as I mentioned earlier, this is not to imply that any of these results necessarily pertain to the main cast of characters. Their fate ultimately depends on the show’s writers and producers, as well as the series’ continued popularity among viewers and the actors’ willingness to stick around.
Note: The idea for this post came from a similar survival analysis applied to characters from Game of Thrones.