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444 APPENDIX: Statistical TablesTABLE A.2SELECTED VALUES FROM THE t DISTRIBUTION*Instructions for use: To find a value of t, locate the row in the left-hand column of the table corresponding to the number ofdegrees of freedom (df) associated with the standard error of the mean, and select the value of t listed for your choice of (nondirectional). The value given in the column labeled .05 is used in the calculation of the 95% confidence interval,and the value given in the column labeled .01 is used to calculate the 99% confidence interval.df .05 .01 df .05 .011 12.71 63.66 18 2.10 2.882 4.30 9.92 19 2.09 2.863 3.18 5.84 20 2.09 2.844 2.78 4.60 21 2.08 2.835 2.57 4.03 22 2.07 2.826 2.45 3.71 23 2.07 2.817 2.36 3.50 24 2.06 2.808 2.31 3.36 25 2.06 2.799 2.26 3.25 26 2.06 2.7810 2.23 3.17 27 2.05 2.7711 2.20 3.11 28 2.05 2.7612 2.18 3.06 29 2.04 2.7613 2.16 3.01 30 2.04 2.7514 2.14 2.98 40 2.02 2.7015 2.13 2.95 60 2.00 2.6616 2.12 2.92 120 1.98 2.6217 2.11 2.90 Infinity 1.96 2.58*This table is adapted from Table 12 in Biometrika Tables for Statisticians, vol. 1 (3d ed.), New York: Cambridge University Press, 1970,edited by E. S. Pearson and H. O. Hartley, by permission of the Biometrika Trustees.