NOTE Murphy: Bias in Chapman-Robson and least-squares estimators of mortality rates 
865 
Table 1 
Percent deviation from true instantaneous total mortality rate (Z) for the mean of 1,000 Chapman-Robson estimates of Z for each 
of the given combinations of sample size and true Z. Frequencies for all age groups were used in calculating mortality rates. 
Sample size 
True Z 
100 
200 
300 
400 
500 
600 
700 
800 
900 
1,000 
0.20 
-0.2 
-0.1 
-0.2 
0.1 
-0.0 
-0.0 
0.1 
0.2 
0.1 
-0.0 
0.40 
-0.1 
0.0 
0.2 
-0.1 
0.3 
-0.1 
0.1 
0.2 
-0.2 
0.2 
0.60 
-0.3 
-0.2 
0.0 
0.0 
-0.1 
-0.0 
-0.2 
0.0 
-0.2 
0.1 
0.80 
-0.1 
-0.2 
0.2 
-0.1 
0.0 
0.2 
0.1 
-0.0 
-0.1 
0.0 
1.00 
0.4 
0.2 
0.4 
-0.1 
-0.0 
0.1 
0.1 
0.1 
0.0 
-0.2 
1.20 
-0.5 
0.2 
0.1 
-0.0 
0.1 
0.0 
0.2 
-0.0 
-0.2 
-0.1 
1.40 
-0.3 
0.3 
-0.1 
0.1 
0.0 
-0.0 
-0.1 
-0.1 
0.0 
-0.1 
1.60 
0.6 
-0.1 
0.2 
0.2 
0.2 
-0.2 
0.1 
-0.1 
-0.1 
-0.1 
1.80 
-0.2 
0.1 
0.1 
-0.1 
0.1 
-0.2 
-0.1 
0.1 
-0.2 
0.2 
2.00 
-0.1 
-0.0 
0.3 
-0.1 
0.0 
-0.2 
-0.2 
-0.1 
0.2 
0.2 
CR and CRt, Z = 0.2 LS, Z = 0.2 
Figure 1 
Percent deviation from true instantaneous total mortality (Z) for the mean of 1,000 Chapman-Robson (CR) or Chapman-Robson- 
for-truncated-data (CRt) estimates of survival or least-squares regression (LS) estimates of equivalent Z for different sample 
sizes when true Z is 0.2 or 2.0. The threshold levels, representing the minimum acceptable abundance for the oldest age used in 
the calculation of mortality were one fish ( — • — ) and five fish ( — O — ). 
