<span class="math inline">\(\psi_k\)</span> is the global parameter relating covariate <span class="math inline">\(k\)</span> to the alpha values. The last possibility included in <code>cxr</code> is for the effect of covariates over alpha values to be interaction-specific, which is coded by specifying ‘alpha_cov_form’ as ‘pairwise’:</p>
<p><span class="math inline">\(\alpha_{ij} + \sum_{k=1}^{s} \psi_{ij} c_k\)</span></p>
<p>In this case, each covariate <span class="math inline">\(c_k\)</span> will