West Coast Groundfish Observer Program Manual, Part2 - NOAA

CHAPTER 5
skates total and 4 skates are going to be sampled
resulting in a sampling unit of 3 (12/4 = 3).
4. Choose which skate to start sampling from by
selecting a random number that is between 1 and the
sample unit (n).
5. Tally sample the randomly selected starting skate
then tally sample every n th skate after that.
Example of Systematic Sampling
1. The Observer on the Blue Dragon verifies with
the skipper that 30 pots have been set.
2. The Observer decides to sample 1/3 of the pots
set.
3. The Observer calculates the number of sampling
units by dividing the total pots by the sample size
(30 total pots / 10 pots = 3 units).
4. The Observer puts pieces of paper with the
numbers 1, 2, and 3 into a hat and randomly
selects the paper with the number 2.
5. The Observer begins tally sampling with pot 2
then samples every third pot after that. Pots 2, 5,
8, 11, 13 etc. are tally sampled by the Observer.
Spatial Sampling
Spatial sampling is gear-based and involves randomly
selecting a portion of skates from the overall set to sample.
The procedure for spatial sampling is as follows:
1. Verify how many skates are in the set.
5-38 1/30/2004