= Solution
The <Student t-distribution> has heavier tails than the <normal distribution>, so unusual personal means need not force the entire population's spread upward or be shrunk as strongly toward its center. The latent $\lambda_i$ allows a large local prior variance for an outlying individual. This <normal scale mixture representation of Student t> is a useful robust version of the <hierarchical Bayesian model>. It still assumes a symmetric, unimodal population; a genuinely multimodal population may need a different model.
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