Natural Resource Biometrics

Sequential Sampling

In sequential sampling, we are taking a sample without knowing the sample size before we start. As opposed to the classical sampling, where we have two possibilities (accept or reject the null hypothesis). In sequential sampling, we have three or more possibilities (accept, reject or uncertainty about the null hypothesis). When you are in the uncertainty condition, you usually continue to sample.

A simple example

In Krebs (1989), he presents an example of rainbow trout put in the effluent coming from a coal processing plant. We know from previous studies that the mean survival time should be less than 36 hours. We follow these steps:

1. Set up the alternatives

H₀: mean survival time <= 36 hours

H₁: mean survival time >= 40 hours

2. Determine the acceptable risk of type I and II error (alpha and beta error)

3. Estimate the threshold

Figure 1 illustrate the how a hypothesis is accepted.

Figure 1: Diagram illustrating a sequential sample for rainbow trout in coal-processing plant effluent

Also See:

Chapter 7 - Sequential Sampling pagess 237--243 in:

Krebs, C. J. 1998. Ecological Methodology. Harper and Row, Publishers. New York. 620 pp.