  An insurance company is required to prepare a certain amount of money, called
reserve, as a mean to pay its policy holders claims in the future. There are
several types of reserve, one of them is IBNR reserve, for which the payments
are made not in the same calendar year as the events that trigger the claims.
Wuthrich and Merz (2015) developed a Bayesian Chain Ladder method for gamma
distribution that applies the Bayesian Theory into the usual Chain Ladder
Method . In this article, we modify the previous Bayesian Chain Ladder for
half-normal distribution, as such distribution is more well suited for lighter
tail claims.
