Fishery bulletin of the Fish and Wildlife Service - NOAA

202 FISHEBY BULLETIN OF THE FISH AND WILDLIFE SERVICE
^ accuracy of the slopes, values of í may be selected for P=0.05, and by substituting
these in the equation,
st
values of b — ß may be calculated which, when added to 6, or subtracted from it, will
give the limits of a range of slope values. The chances will then be 19 out of 20
that the true slope lies within this range.
From these calculated ranges (table 11), it is clear that there was so little random
variability of the points about the Unes of best fit, that mortality values are accurate
to within one or 2 percent per day for all segments other than A to C.
There still remains the question: which of these combinations of straight lines
gives the most probably true series of survival rates? This may be investigated by
the formula for the significance of the difference of two slopes, again going through
the í test, using the formula
where
те'-4
From the results given in table 11, where the subscripts of 6 represent the initial and
terminal points of the segments, it is apparent: (1) That ЬА-С differs from & 4 _ 8 just
enough to indicate that the survival rate probably is significantly higher in the larval
stages than in the egg, and therefore the two lines A-C and 4-8 better describe this
segment than the one line A-9. However, the latter does not differ significantly
enough from each of the former to preclude the possibility that it fairly well represents
the general course of survival from the early egg stage to the 9-mm. larva.
(2) That î»n_2î is certainly significantly different from i>A-e, though not from Z>4_8.
The interpretation of these findings will be discussed in the following section.
Segment
A-C ... . -.
4-8 ....
A-9 i. .
11-22 -- ...
TABLE 11.—Estimates of accuracy of slopes of lines in figure 17
6
-0. 02246
-.05465
-.06521
-.07407
j
0. 0307
.0337
.0905
.1166
ь-е
0.1170
.00716
.00515
.0128
Equivalent mortality rates fa percent per
day
Indicated