# Assurances et véhicules autonomes

Lundi matin, j’interviendrai dans un séminaire organisé par Stève Bernardin, sur le thème  “assurances et véhicules autonomes”, avec comme autres participants Philippe Talleux, Romain Cros, David Zuby et Jonathan Charak. En guise d’introduction, je peux renvoyer vers deux articles que nous avions écrit avec Rodolphe Bigot, Repenser la responsabilité, et la causalité et surtout Quelle responsabilité pour les algorithmes ?

# Louis Bachelier Fellowship

I am delighted and honored to have been inducted as Academic Fellow by Institut Louis Bachelier. It’s a great opportunity to join such a distinguished group of scholars !

Louis Bachelier Fellows

# From multinomial regression to binary classification on some Siamese data

There are two kinds of people in the world: people who think there are two kinds of people in the world and people who don’t

(borrowed from Menand (2018)). Because things are always simpler when we face only binary choice, aren’t they? But consider here the case were multiple options are possible, and let us see if we cannot get back to simpler binary choices. Consider a collection of observations $(y_i,\boldsymbol{x}_i)$ where $y_i$ is some categorical variable, $y_i\in\mathcal{A}$ where $\mathcal{A}=\lbrace A_1,\cdots,A_\kappa \rbrace$, with $\kappa$ possible categories. Let $\mathcal{I}_k=\lbrace i:y_i\in A_k \rbrace$.

In a classical multinomial logistic regression, suppose that $A_1$ is the reference, then $$\mathbb{P}[Y=A_j|\boldsymbol{X}=\boldsymbol{x}]=\frac{\exp[\boldsymbol{x}^\top\boldsymbol{\beta}_j]}{1+\exp[\boldsymbol{x}^\top\boldsymbol{\beta}_2]+\cdots+\exp[\boldsymbol{x}^\top\boldsymbol{\beta}_k]}$$With a lot a categories, and a small number of observations, inference can be complicated, and non-robust.

• the Siamese dataset

The name Siamese I use, here, comes from Siamese Networks. Or sort of… As we say in French, it is an « histoire de l’homme qui a vu l’homme qui a vu l’ours » (story of the man who saw the man who saw the bear). A few years ago, a student tried to explain to me the idea of Siamese Networks and this is what I understood. I might be completely wrong, but the idea I got from it did make sense, in my mind at least. That is the story of that blog post…

The idea of the siamese algorithm will be to consider all pairs of observations, $(y_i,\boldsymbol{x}_i)$ and $(y_j,\boldsymbol{x}_j)$ :

1. $\tilde y_{i,j}=\boldsymbol{1}(y_i=y_j)$ indicating if individuals $i$ and $j$ are in the same category
2. $\tilde{\boldsymbol{x}}_{i,j}$ is a collection of $p-1$ variables,
• $\tilde {x}_{k:i,j}={x}_{k:i}-{x}_{k:j}$ if $x_k$ is continuous, or $\tilde {x}_{k:i,j}=|{x}_{k:i}-{x}_{k:j}|$ (we can use another metric, e.g. $\tilde {x}_{k:i,j}=|{x}_{k:i}-{x}_{k:j}|^2$, and this is why I decided to use some GAM model in the logistic regression on the Siamese dataset)
• $\tilde {x}_{k:i,j}=({x}_{k:i},{x}_{k:j})\in\mathcal{X}_k\times\mathcal{X}_k$ if $x_k$ is a categorical variables (taking values in the set $\mathcal{X}_k$), or $\tilde {x}_{k:i,j}=\boldsymbol{1}({x}_{k:i}\neq{x}_{k:j})\in\{0,1\}$

The original dataset was a $n\times p$ matrix, and (if there are no categorical variable), it becomes a $n(n-1)/2\times p$ matrix. The key point is that if the original variable $y_i$ was multinomial, $y_{i,j}$ is now binomial. For instance, if our initial dataset was the following, with two covariates, one continuous and one categorical

its siamese counterpart is the following

• Classification step

On the dataset $(\tilde y_{i,j},\tilde {x}_{k:i,j})_{i,j}$, fit a logistic regression, $$\mathbb{P}[\tilde Y|\tilde{\boldsymbol{X}}=\tilde{\boldsymbol{x}}]=\frac{\exp[\tilde{\boldsymbol{x}}^\top\boldsymbol{\beta}]}{1+\exp[\tilde{\boldsymbol{x}}^\top\boldsymbol{\beta}]}$$(or any classification model – CART, random forest, etc). But that is the easy part (unless $n$ is large, because the siamese dataset has (roughly) $n^2/2$ rows). The difficult task is the prediction

• Prediction step

Consider a new input variable $\boldsymbol{x}_{\cdot}$, and define its siamese version, $\tilde{\boldsymbol{x}}_{\cdot}=(\tilde{\boldsymbol{x}}_{\cdot,j})_j$, i.e. a database with $n$ rows. Then compute
$$p_{\cdot,j}=\mathbb{P}[\tilde Y|\tilde{\boldsymbol{X}}=\tilde{\boldsymbol{x}}_{\cdot,j}]=\frac{\exp[\tilde{\boldsymbol{x}}_{\cdot,j}^\top\boldsymbol{\beta}]}{1+\exp[\tilde{\boldsymbol{x}}_{\cdot,j}^\top\boldsymbol{\beta}]}$$ where $p_{\cdot,j}$ is the probability that $(y_j,\boldsymbol{x}_{j})$ and $(y_{\cdot},\boldsymbol{x}_{\cdot})$ are in the same category, as well as $$p_{i,j}=\mathbb{P}[\tilde Y|\tilde{\boldsymbol{X}}=\tilde{\boldsymbol{x}}_{i,j}]=\frac{\exp[\tilde{\boldsymbol{x}}_{i,j}^\top\boldsymbol{\beta}]}{1+\exp[\tilde{\boldsymbol{x}}_{i,j}^\top\boldsymbol{\beta}]}$$
Let $\boldsymbol{p}_{\cdot}=(p_{\cdot,j})$, and similarly $\boldsymbol{p}_{i}=(p_{i,j})$. Then several techniques can be used to predict $y_{\cdot}$.

1. $\widehat{y}_{\cdot}=y_{j^\star}$ where ${j^\star}=\underset{j=1,\cdots,n}{\text{argmax}}\{p_{\cdot,j}\}$: the predicted class is the one of the observation the most likely to be other same class
2. $\widehat{y}_{\cdot}=y_{j^\star}$ where ${j^\star}=\underset{\ell=1,\cdots,k}{\text{argmax}}\{\overline{p}_{\ell}\}$, where$$\overline{p}_{\ell} = \frac{1}{n_{\ell}}\sum_{j\in\mathcal{I}_s} \boldsymbol{1}(y_j =y_{\ell}),\text{ where }\mathcal{I}_s=\lbrace i:p_{\cdot,i}>s\rbrace$$consider only probabilities sufficiently high to be considered, and predict the most important class (majority rule)
3. $\widehat{y}_{\cdot}=y_{j^\star}$ where $${j^\star}=\underset{i=1,\cdots,n}{\text{argmax}}\{\theta_i\}$$ where $$\theta_i=\cos(\boldsymbol{p}_{\cdot},\boldsymbol{p}_{i})=\displaystyle{\frac{\boldsymbol{p}_{\cdot}\cdot\boldsymbol{p}_{i}}{\|\boldsymbol{p}_{\cdot}\|\|\boldsymbol{p}_{i}\|}}$$
4. $\widehat{y}_{\cdot}=y_{j^\star}$ where $${j^\star}=\underset{i=1,\cdots,n}{\text{argmax}}\{KL_{\cdot|i}\}$$ and $KL_{\cdot|i}=\displaystyle{\sum_{j=1}^n p_{\cdot,j}\log\frac{p_{\cdot,j}}{p_{i,j}}}$ (but one can select another metric)
5. $\widehat{y}_{\cdot}=y_{j^\star}$ where ${j^\star}=\underset{j\in\mathcal{J}}{\text{argmax}}\{p_{\cdot,j}\}$ and $\mathcal{J}$ is a sample of $k$ observations, chosen randomly, one in each group (one-shot procedure): the predicted class is the one of the observation the most likely to be other same class

Heuristically, it can be related to some $k$ nearest neighbors strategy: we give the attribute that most neighbors have. The total distance is a weighted sum of the componentwise distances (for the logistic regression).

• Simulation study

In order to test that technique, let us generate some multinomial model where $y$ has 10 possible labels, with 6 (independent) covariates $x_1,\cdots,x_6$, and $\mathbb{P}[Y=A_k|\boldsymbol{X}=\boldsymbol{x}]\propto \exp[\boldsymbol{x}^\top\boldsymbol{\beta}_k]$ (where coefficients $\boldsymbol{\beta}_k$ where generated randomly) for $k\in\{1,2,\cdots,10\}$ (there were 10 categories) and with $n=700$ observations.

n=700 X1=rnorm(n) X2=rnorm(n) X3=rnorm(n) X4=rnorm(n) X5=rnorm(n) X6=rnorm(n) X=cbind(1,X1,X2,X3,sqrt(abs(X4)),X5*X1,X6) k = 10 PARAM = matrix(rnorm(k*6),k,6) PARAM[,1]=PARAM[,1]-1 PARAM=cbind(PARAM,0) P=matrix(NA,n,k-1) for(j in 1:(k-1)) P[,j] = X %*% (PARAM[j,])+rnorm(n) P=cbind(P,0) S=apply(exp(P),1,sum) Pb = exp(P)/S tirage = function(i){ sample(1:10,size=1,prob = Pb[i,]) } Y = LETTERS[Vectorize(tirage)(1:n)] dbase = data.frame(Y=as.factor(Y),X1,X2,X3,X4,X5)

In the paragraph previously, I suggested to take the most likely one. Being wrong means that it was not the first choice. But perhaps being the second or the third choice is not that bad, actually. So in my simulations, I look at the proportion of predictions were our prediction is the good one (top 1), if the true one is either the most likely or the second most likely (top 2), or in the top 3. That will be on my $x$-axis. I draw some line, but we simply have three points (top 1, top 2 and top 3). I compute the proportion of good prediction, using cross-validation techniques (10-fold). The black lines are one of the methods described above. The red one is the standard multinomial model (with a logistic link function). For the Siamese model, I tried several models. I tried a logistic regression, and some smooth version (GAM) on top

and a classification tree, on the left, as well as some random forest on the right, below.

It looks like the multinomial approach performs always better than any Siamese one… and to be honest, I am disappointed.

Here is the code I did use when I considered a logistic regression on the Siamese dataset,

set.seed(1) kfold = sample(rep(1:10,n/10))   KFOLDglm = function(i){ i_test=which(kfold==i) i_calibration=which(kfold!=i) y=credit[i_calibration,"Y"] tirage = function(){ v=c(sample(i_calibration[y==levels(y)[1]],size=1), sample(i_calibration[y==levels(y)[2]],size=1), sample(i_calibration[y==levels(y)[3]],size=1), sample(i_calibration[y==levels(y)[4]],size=1), sample(i_calibration[y==levels(y)[5]],size=1), sample(i_calibration[y==levels(y)[6]],size=1), sample(i_calibration[y==levels(y)[7]],size=1), sample(i_calibration[y==levels(y)[8]],size=1), sample(i_calibration[y==levels(y)[9]],size=1), sample(i_calibration[y==levels(y)[10]],size=1)) names(v)=levels(y) return(v) }   LogisticModel &lt;- multinom(Y ~ ., data = credit[i_calibration,], trace=FALSE)   comparaisonx = function(base,x=base[1,]){ mix_base = base for(j in 1:ncol(base)){ xj = as.numeric(x[j])-base[,j] mix_base[,j] = (xj) } mix_base } comparaisony = function(base,y=base[1]){ as.factor(base == y) } creditx = credit[,-which(names(credit) == "Y")] nc=length(i_calibration) B=comparaisonx(base = creditx[i_calibration[2:nc],],x=creditx[i_calibration[1],]) B$Y=comparaisony(base = credit[i_calibration[2:nc],"Y"],y=credit[i_calibration[1],"Y"]) for(i in 2:(nc-1)){ B0=comparaisonx(base = creditx[i_calibration[(i+1):nc],],x=creditx[i_calibration[i],]) B0$Y=comparaisony(base = credit[i_calibration[(i+1):nc],"Y"],y=credit[i_calibration[i],"Y"]) B=rbind(B,B0) } credit_mix = B   OneShotLogisticModel &lt;- glm(Y ~ ., data = credit_mix, family=binomial) A_ref = table(credit[i_calibration,"Y"])/length(i_calibration)   vect_oneshot = function(i){ B2=comparaisonx(base = creditx[i_calibration,],x=creditx[i,]) predict(OneShotLogisticModel,type="response",newdata=B2) }   prediction_oneshot = function(i,type=1){ B2=comparaisonx(base = creditx[i_calibration,],x=creditx[i,]) p=predict(OneShotLogisticModel,type="response",newdata=B2) y=credit[i_calibration,"Y"] base = data.frame(p,y) base = base[rev(order(base$p)),] if(type==1){T = table(base$y[1:11]) return(names(which.max(T)))} if(type==2){return(base$y[1])} if(type==3){A=table(base$y[1:10])/10 T=A/A_ref return(names(which.max(T)))} if(type==4){ costheta = rep(NA,length(i_calibration)) for(j in 1:length(i_calibration)){ vecteur_proba = vect_oneshot(i_calibration[j]) costheta[j] = sum(vecteur_proba*p)/(sqrt(sum(vecteur_proba^2))*sqrt(sum(p^2))) } return(y[which.max(costheta)])} if(type==5){ kl = rep(NA,length(i_calibration)) for(j in 1:length(i_calibration)){ vecteur_proba = vect_oneshot(i_calibration[j]) kl[j] = sum(p*log(vecteur_proba/p)) } return(y[which.max(as.vector(kl))])} if(type==6){ ## one shot : tirer au hasard un de chaque, et dire lequel est plus credible !   y=credit[i_calibration,"Y"] tirage = function(){ v=c(sample(i_calibration[y==levels(y)[1]],size=1), sample(i_calibration[y==levels(y)[2]],size=1), sample(i_calibration[y==levels(y)[3]],size=1), sample(i_calibration[y==levels(y)[4]],size=1), sample(i_calibration[y==levels(y)[5]],size=1), sample(i_calibration[y==levels(y)[6]],size=1), sample(i_calibration[y==levels(y)[7]],size=1), sample(i_calibration[y==levels(y)[8]],size=1), sample(i_calibration[y==levels(y)[9]],size=1), sample(i_calibration[y==levels(y)[10]],size=1)) names(v)=levels(y) return(v) } pd=rep(NA,101) for(ix in 1:101){ ids = tirage() B2=comparaisonx(base = creditx[ids,],x=creditx[i,]) p=predict(OneShotLogisticModel,type="response",newdata=B2) pd[ix]=levels(y)[which.max(p)] } levels(y)[which.max(table(pd))] } } PRED0=as.character(credit[i_test,"Y"]) PRED1=as.character(predict(LogisticModel,type = "class", newdata=credit[i_test,])) PRED21=as.character(Vectorize(function(i) prediction_oneshot(i,type=1)) (i_test)) PRED22=as.character(Vectorize(function(i) prediction_oneshot(i,type=2))(i_test)) PRED23=as.character(Vectorize(function(i) prediction_oneshot(i,type=3))(i_test)) PRED24=as.character(Vectorize(function(i) prediction_oneshot(i,type=4))(i_test)) PRED25=as.character(Vectorize(function(i) prediction_oneshot(i,type=5))(i_test)) PRED26=as.character(Vectorize(function(i) prediction_oneshot(i,type=6))(i_test)) B=data.frame(PRED0,PRED1,PRED21,PRED22,PRED23,PRED24,PRED25,PRED26) B }   s=1/100;setTxtProgressBar(pb, s*2) for(i in 2:10){ PREDICTION = rbind(PREDICTION,KFOLDglm(i)) s=s+1/100;setTxtProgressBar(pb, s*2)} for(j in 1:5) PREDICTION[,j]=as.character(PREDICTION[,j]) L=list() v=mean(PREDICTION[,1]!=PREDICTION[,2]) names(v)="logistic" L[["logistic"]]=v v=c(mean(PREDICTION[,1]!=PREDICTION[,3]), mean(PREDICTION[,1]!=PREDICTION[,4]), mean(PREDICTION[,1]!=PREDICTION[,5]), mean(PREDICTION[,1]!=PREDICTION[,6]), mean(PREDICTION[,1]!=PREDICTION[,7]), mean(PREDICTION[,1]!=PREDICTION[,8])) names(v)=c("top10","max","10norm","cos","KL","OS") L[["glm"]]=v

# Autocalibration for Insurance Pricing with Machine Learning

With Michel Denuit and Julien Trufin, we recently uploaded a joint paper on ArXiv, entitled Autocalibration and Tweedie-dominance for Insurance Pricing with Machine Learning.

Boosting techniques and neural networks are particularly effective machine learning methods for insurance pricing.
Often in practice, there are nevertheless endless debates about the choice of the right loss function to be used to train the machine learning model, as well as about the appropriate metric to assess the performances of competing models. Also,
the sum of fitted values can depart from the observed totals to a large extent and this often confuses actuarial analysts.
The lack of balance inherent to training models by minimizing deviance outside the familiar GLM with canonical
link setting has been empirically documented in Wüthrich (2019, 2020) who attributes it to the early stopping rule in gradient descent methods for model fitting.
The present paper aims to further study this phenomenon when learning proceeds by minimizing Tweedie deviance.
It is shown that minimizing deviance involves a trade-off between the integral of weighted differences of lower partial moments and the bias measured on a specific scale.
Autocalibration is then proposed as a remedy. This new method to correct for bias adds an extra local GLM step to the analysis.
Theoretically, it is shown that it implements the autocalibration concept in pure premium calculation and ensures that balance also holds on a local scale, not only at portfolio level as with existing bias-correction techniques. The convex order appears to be the natural tool to compare competing models, putting a new light on the diagnostic graphs and associated metrics proposed by Denuit et al. (2019).

In this paper, we started with a simple observation : with GLM (like a Poisson regression) we have unbiased predictions, in the sense that $\widehat{y}_1+...+\widehat{y}_n=y_1+...+y_n$ (on the training dataset, we should expect to have $\widehat{y}_1+...+\widehat{y}_n\approx y_1+...+y_n$ on the validation dataset). But with any machin learning algorithm, this is no longer the case. For instance, with a boosting algorithm, we can end up with a significant bias. This is an application on an insurance dataset from the CASdataset package, with a GLM (Poisson regression) on the left, and additive smooth version, GAM in the middle and some boosting algorithm on the right. Here is the dispersion of the predictions, $\widehat{y}_i$‘s,

Let $\widehat{\pi}$ denote a fited model. If $\widehat{\pi}$ was close to the true parameter of the Poisson model, $\mu$ where $\mu(\boldsymbol{x})=\mathbb{E}[Y|\boldsymbol{X}=\boldsymbol{x}]$, then function  $s\mapsto\mathbb{E}[Y|\widehat{\pi}(\boldsymbol{X})=s]$ should be very close to the first diagonal (since $\mathbb{E}[Y|\mu(\boldsymbol{X})=s]=s$). And this is was we observe below, for the GLM. But the boosting algorithm has a significant bias.

Furthermore, the bias is not the same everywhere. We can see it more precisely on a quantile version of the $x$-axis

that is $u\mapsto\mathbb{E}[Y|\widehat{\pi}(\boldsymbol{X})=F_{\widehat{\pi}}^{-1}(u)]$. Here is a multiplicative version of that bias $u\mapsto\mathbb{E}[Y|\widehat{\pi}(\boldsymbol{X})=F_{\widehat{\pi}}^{-1}(u)]/u$

The idea of autocalibration is to use that multiplicative factor to correct from the bias. Thus, if $\widehat{\pi}(\boldsymbol{x})$ is close to the 75% upper quantile, then the true value should be 20% larger for the bootsting algorithm. Here is the new distribution of the predictions, with that correction

and we can observe that $u\mapsto\mathbb{E}[Y|\widehat{\pi}(\boldsymbol{X})=F_{\widehat{\pi}}^{-1}(u)]$ is now much closer to the first diagonal (below is the multiplicative bias)

We discuss in the paper this correction for local bias, so that $u\mapsto\mathbb{E}[Y|\widehat{\pi}(\boldsymbol{X})=F_{\widehat{\pi}}^{-1}(u)]$ becomes as close as possible to the first diagonal… see https://arxiv.org/abs/2103.03635 for a complete version of the paper, and https://github.com/freakonometrics/autocalibration/ for the complete version of the R codes

# Unusual data for insurance, joint research initiative

We recently started a joint research initiative, funded by the AXA Research Fund, to work on unusual data for insurance

Insurers sometimes lack information at the time of claim submission, such as the structure of a building, the presence of health risks common to a group of people, or the spatial diffusion of a pandemic. Unusual data, such as satellite images, personal network connections, and tweets can be used to populate this information gap. In this joint research initiative, we will use images, network data, and texts for risk analysis from an actuarial perspective. Specifically, the project will explore how using unusual data can contribute to smoother claims assessment and reduced data quality risk, allowing for better risk selection and pricing. The project will look at three types of unusual data: pictures/satellite images, network data, and text data.

More information will be shared via a dedicated website (https://jridata.github.io/), even if I will also mention interesting papers, conferences and open-source codes on this blog….