\begin{figure*}[b]
    \centering
<<fig=TRUE,height=3>>=
    model <- models
    model$archive.report <- NULL
    model$display_order <- unlist(by(model, model$project, function(x) order(order(x$bug_number))))
    model <- melt(model, id.vars=c('project', 'bug_number', 'bug_id', 'display_order'))
    model$project <- format_name(model$project)
    model$variable <- format_name(model$variable)
    legend = guide_legend(nrow=2)
    fig <- ggplot(model, aes(display_order, value, linetype=variable, colour=variable)) +
        geom_line() +
        coord_cartesian(ylim=c(-2, 2)) +
        facet_grid(. ~ project, scales='free') +
        labs(x='', y='Coefficient') +
        guides(linetype=legend) +
        theme(axis.text=element_text(colour='black'),
              axis.text.x=element_text(angle=90),
              legend.position='bottom',
              legend.title=element_blank(),
              panel.border=element_rect(colour='black', fill=NA)
        )
    print(fig)
@
    \caption{Coefficient for each model parameter over time. Bugs in order of report date.}
    \label{fig:model}
\end{figure*}
