Effect of Fg concentration on integrin cluster shape. Integrin cluster shape is characterized by the cluster eccentricity. (a) and (b) show example empirical frequency distributions and corresponding beta distributions for integrin clusters in cells adhering to 10 μg/mL Fg, and 200 μg/mL Fg, respectively. (c) and (d) show the effect of ECM density on the least squares estimates for the beta distribution parameters, along with 95% confidence intervals for the parameter estimates. (e) shows the calculated expected (mean) value for the distribution of integrin cluster shapes in cells adhering to each Fg concentration.