Table 1.

Summary of analysis results for 1000 simulated studies of before–after differences in copies per million cells, using four different analysis methods (see Box 2 and text)

Method	Median estimated fold reduction	Median absolute error (log10 scale)	95% CI coverage (%)*	Power (%)
Input fixed at 1,000,000 cells. Copies counted exactly.
A. 0 copies reset to 1, paired t-test	2.03	0.29	27.1	81.9
B. Add 1 to copies, paired t-test	2.08	0.28	22.3	86.4
C. 0 copies treated as left-censored	2.66	0.18	77.1	87.5
D. Negative binomial regression	3.20	0.15	88.1	89.5
Input fixed at 1,000,000 cells. Copies measured with error.
A. 0 copies reset to 1, paired t-test	2.03	0.29	29.2	77.0
B. Add 1 to copies, paired t-test	2.11	0.28	25.6	83.4
C. 0 copies treated as left-censored	2.78	0.17	80.6	83.6
D. Negative binomial regression	3.30	0.15	87.4	85.8
Input varies from 500,000 to 1,500,000 cells. Copies counted exactly.
A. 0 copies reset to 1, paired t-test	2.01	0.30	24.5	75.7
B. Add 1 to copies, paired t-test	2.08	0.28	23.2	82.9
C. 0 copies treated as left-censored	2.71	0.17	76.6	85.7
D. Negative binomial regression	3.23	0.14	87.5	87.3
Input varies from 500,000 to 1,500,000 cells. Copies measured with error.
A. 0 copies reset to 1, paired t-test	2.00	0.30	26.0	72.3
B. Add 1 to copies, paired t-test	2.09	0.28	28.2	79.5
C. 0 copies treated as left-censored	2.77	0.16	81.6	81.7
D. Negative binomial regression	3.23	0.15	87.4	85.0

CI: confidence interval.

Each study includes N = 12 persons, and the true mean reduction in log(copies per million cells) corresponds to a fourfold reduction in copies per million cells.

*For CIs, the ideal value for coverage is 95%.