def acts(self):
        """The autocorrelation times of each parameter.

        The autocorrelation time is defined as the ACL times the
        ``thin_interval``. It gives the number of iterations between
        independent samples.
        """
        if self.acls is None:
            return None
        return {p: acl * self.get_thin_interval()
                for (p, acl) in self.acls.items()}