CONTENTS. 
CHAPTER XVIL 
THE SIMPLER CASES OF SAMPLING FOR VARIABLES: 
PERCENTILES AND MEAN. 
PAGES 
1-2. The problem of sampling for variables : the conditions 
assumed—3. Standard error of a percentile—4. Special 
values for the percentiles of a normal distribution—5. 
Effect of the form of the distribution generally—6. Simplified 
formula for the case of a grouped frequency-distribution—7. 
Correlation between errors in two percentiles of the same 
distribution—8. Standard error of the interquartile range 
for the normal curve—9. Effect of removing the restrictions 
of simple sampling, and limitations of interpretation—10. 
Standard error of the arithmetic mean—11. Relative sta- 
bility of mean and median in sampling—12. Standard error 
of the difference between two means—13. The tendency to 
normality of a distribution of means—14. Effect of removing 
the restrictions of simple sampling—15. Statement of the 
standard errors of standard-deviation, coefficient of variation, 
correlation-coefficient, and regression—16, Restatement of 
the limitations of interpretation if the sample be small . 3835-356 
ApPENDIX I.—Tables for facilitating Statistical Work . , 357-359 
ArpENDIX II.—Short List of Works on the Mathematical Theory 
of Statistics, and the Theory of Probability . 360-361 
SUPPLEMENTS — 
I. NorEs SUPPLEMENTARY TO CHAP. VI. . . 362-364 
II. Direct DEDUCTION OF THE FOoRMULE FOR REGRESSIONS 365-366 
[II. THE LAW oF SMALL CHANCES 366-370 
[V. GoopNEss oF Fir 370-389 
ADDITIONAL REFERENCES . 390-398 
ANSWERS TO, AND HINTS oN THE SOLUTION OF, THE EXERCISES 
GIVEN . 399-406 
INDEX. . 407-422 
XV