Limiting dilution analyses of bone nodule-forming capacity. Linear regression analysis was performed to show the relationship between the fraction of the nonresponsive wells against plated cell number for the different sorted cell populations and the parent FRCC population. Results are expressed as mean ± 95% confidence limits. R is the correlation coefficient. F_0.37 is an estimate of the mean number of cells that would include one progenitor cell, based on application of the Poisson distribution.