The Amazon River Basin Includes the Largest Remaining Connected Area $\begin{array} { l c c c c c c c } \text { Unflooded } & 123 & 137 & 106 & 77 & 103 & 79 & 195 \\ & 227 & 182 & & & & & \end{array}$

question 25

Essay

The Amazon River basin includes the largest remaining connected area of tropical
forest in the world, and ecologists regularly monitor its health. One aspect of its
health is the density of different indigenous species. The Amazon basin includes both
areas that are periodically flooded, and areas that are not periodically flooded. If the
densities of species differ in the flooded and unflooded regions, researchers will want
to take stratified samples in their studies. Stratified sampling would be more
expensive, since boats must be rented to get to any randomly selected flooded sites.
The data below are measures of density (individuals per square kilometer) of primates
in random samples of flooded and unflooded areas in the Amazon basin. Primate density
$\begin{array} { l c c c c c c c } \text { Unflooded } & 123 & 137 & 106 & 77 & 103 & 79 & 195 \\ & 227 & 182 & & & & & \end{array}$
$\begin{array} { l l l l l l } \text { Flooded } & 201 & 126 & 185 & 355 & 344 \end{array}$ a) Do these data provide convincing evidence of a difference in the primate density
in flooded and unflooded forests in Amazonia? Provide appropriate statistical
justification for your conclusion.
b) Based on your results in part (a), would you recommend using a stratified sample?
Justify your recommendation with a statistical argument.

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Definitions:

Construct Validity

The degree to which a measurement device accurately measures the theoretical construct it is designed to measure.

Reliability

The consistency and stability of measurements or assessments over time.

Validity

The degree to which a tool, test, or measure accurately represents or measures what it claims to.

Variability

The extent to which data points in a set differ from each other and from the average, indicating the spread or dispersion.