Your Textbook Extends the Simple Regression Analysis of Chapters 4 $\widehat { \text { TestScore } } = 698.9 - 2.28 \times \text { STR }$

question 17

Essay

Your textbook extends the simple regression analysis of Chapters 4 and 5 by adding an
additional explanatory variable, the percent of English learners in school districts (PctEl).
The results are as follows: $\widehat { \text { TestScore } } = 698.9 - 2.28 \times \text { STR }$
$\text {and}$
$\widehat { \text { TestScore } } = 686.0 - 1.10 \times S T R - 0.65 \times \text { PctEL }$ Explain why you think the coefficient on the student-teacher ratio has changed so
dramatically (been more than halved).

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Definitions:

Ecological Efficiency

The efficiency with which energy is transferred from one trophic level to the next in an ecosystem. Typically only a small percentage of energy is passed on to the next level.

Trophic Level

A step in a food chain or food web, representing the position of organisms in the flow of energy through an ecosystem.

Percentage

A mathematical term representing a fraction of 100, used to describe proportions or ratios.

Fresh Water

Water that contains minimal amounts of dissolved salts, especially found in lakes, rivers, and streams, as opposed to salt water.