Figure 4: Correlation and prediction of in vivo bone formation with in vitro factors. Empirical modelling was carried out to find the combination of in vitro factors that are predictive of ectopic in vivo bone formation. A: in vitro and in vivo measurements clustered according to their pairwise correlations. B: variable importance plot generated by a first partial least square regression (PLSR) model including all in vitro measurements. Only variables with a importance larger than 0.8 (underlined) have been retained for the final PLSR model. C: Results of the final PLSR model showing the predicted versus measured (‘actual’) values (top) for the percent of bone formed in vivo in Copios™ (left) and Collagraft™ (right) carriers. The bottom row shows the difference between measured and predicted values. Symbols are defined as follows: □: control 1; ◊: control 2; Δ: N540K; o: G380R.