Sampling Techniques Part 2

Questions and Answers

What two aspects must be considered when focusing on scale and study plots?

Mean and variance

Randomization and selection

Species richness and productivity

Focus and extent (correct)

What is the primary purpose of randomization in sampling?

To enhance the size of the observational area

To minimize the chances of bias in estimates (correct)

To ensure complete representation of all strata

To calculate traditional measures of variance

Which sampling design involves dividing the sampling space into subunits before selection?

Stratified random sampling (correct)

Cluster sampling

Simple random sampling

Systematic sampling

What is a potential drawback of simple random sampling?

It can result in clumping of observation locations. Signup and view all the answers

What does 'inference space' refer to in sampling design?

The broad area represented by the sample observations Signup and view all the answers

What type of statistical tests rely on randomization for their fundamental assumptions?

Inferential statistics Signup and view all the answers

In simple random sampling, how is the selection of one observational unit related to another?

Independent of the selection of another unit Signup and view all the answers

What is the main characteristic of simple random sampling as a statistical method?

All units have an equal chance of selection. Signup and view all the answers

What is the purpose of using strata in sampling?

To identify meaningful strata that influence the outcome Signup and view all the answers

How is the standard error from stratified random sampling calculated?

Using the proportion of samples in each strata with their variances Signup and view all the answers

What impact does having more strata have on observations?

It increases the chance of obtaining meaningless strata. Signup and view all the answers

What is a key characteristic of systematic sampling?

The initial point is selected randomly and spacing is equal. Signup and view all the answers

What is a common misconception about estimating standard error in systematic sampling?

It can be estimated using a single systematic sample. Signup and view all the answers

In the weighting calculation for means and variances based on strata, what does nh represent?

The total number of [area] units in strata h Signup and view all the answers

What does the equation for standard error from stratified sampling include?

The proportion of samples in strata with the corresponding variances Signup and view all the answers

What does a high variance within strata imply for sampling?

There is significant variability in the data collected. Signup and view all the answers

Study Notes

Scale and Study Plots

Two key aspects: Focus refers to the physical area represented by observation units; Extent encompasses the physical area over which those units are distributed.
Balancing these factors involves considering how many observations are needed, appropriate observation size, and the broader inference space represented by the sample.

Randomization

Random selection is crucial for obtaining unbiased estimates of mean and variance in a statistical population.
This randomness is a fundamental assumption for many statistical tests, affecting the reliability of results.
Various methods exist for random selection, such as using random number generators or tables.

Sampling Designs

Simple Random Sampling: Every observational unit has an equal probability of selection, ensuring independence between selections. Effective for representation but may be inefficient in spatially patterned environments.
Potential for clumping can undermine the representation of a statistical population.
Stratified Random Sampling: Involves dividing the sampling space into strata and selecting observations randomly from each. Important to choose meaningful strata to ensure relevance and adequacy of observations.
Systematic Sampling: Involves equal spacing in sample selection, initiated by a randomly chosen first point, facilitating systematic coverage of the study area.

Statistical Considerations

Weights may be necessary for calculating mean and variance when sample sizes vary between strata.
Standard error calculation in stratified sampling accounts for sample proportion in each stratum.
One systematic sample cannot provide an estimate of standard error, regardless of the number of observations taken.

Important References

Waide et al., 1999, discusses the interplay between productivity and species richness, emphasizing ecological dynamics.
Chalcraft et al., 2004, explores scale dependence within species richness and productivity relationships, highlighting species turnover's role.

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Description

This quiz covers advanced topics in sampling techniques, specifically focusing on scale and study plots. Explore different kinds of sampling designs and the importance of randomization in ecological studies. Ideal for students studying ecology and statistics.