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Chapter 4: Problem 51

Identify the experimental units or subjects, the explanatory variables (factors), the treatments, and the response variables. Ability to grow in shade may help pines found in the dry forests of Arizona to resist drought. How well do these pines grow in shade? Investigators planted pine seedlings in a greenhouse in either full light, light reduced to 25% of normal by shade cloth, or light reduced to 5% of normal. At the end of the study, they dried the young trees and weighed them.

Short Answer

Expert verified
The seedlings are subjects, light levels are factors/treatments, and weight is the response variable.

Step by step solution

01

Identify Experimental Units or Subjects

The experimental units or subjects in this experiment are the pine seedlings that were planted in the greenhouse. The seedlings are the primary focus of the study, as they are the objects being observed and measured.
02

Identify Explanatory Variables (Factors)

The explanatory variable, also known as the factor, in this study is the level of light exposure that the seedlings receive. This variable is manipulated by the investigators to study its effect on the seedlings' growth.
03

Identify Treatments

The treatments are the different levels of the explanatory variable applied to the subjects. In this case, the treatments are the levels of light exposure: full light, 25% light, and 5% light.
04

Identify Response Variables

The response variable is what the investigators measure to determine the effect of the treatments. Here, the response variable is the weight of the dried young trees at the end of the study, which indicates how well the pines grow under the different lighting conditions.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Experimental Units
In an experiment, the experimental units are the primary focus. They are the objects or subjects that researchers are most interested in studying. In the experiment concerning pine seedlings, these units are the trees themselves. The seedlings were chosen to understand how they grow under different light conditions.
It's important to identify experimental units because they help in organizing the experiment and ensuring that the data collected is meaningful and relevant.
  • Experimental units can be living organisms, like plants or animals.
  • They can also be non-living things, like plots of land or physical materials.
Each unit is observed, often under varying conditions, to gather data that contributes to the overall findings of the study.
Explanatory Variables
Explanatory variables, also known as independent variables or factors, are the variables that researchers manipulate in an experiment. In the case of the pine seedlings, the explanatory variable is the level of light exposure. This is deliberately changed to explore its effect on the seedlings' growth.
When identifying explanatory variables, it鈥檚 crucial to recognize that these are the aspects of the experiment that can be controlled or altered.
  • In the seedling experiment, light was altered to create different growth conditions.
  • Other experiments might manipulate temperature, dosage of a drug, or hours of study.
The purpose of manipulating the explanatory variable is to see how changes in that variable affect the outcome of the experiment, which is measured through the response variable.
Response Variables
The response variable is what you measure in an experiment, often seen as the effect or outcome of changing the explanatory variable. For the pine seedlings, the response variable was the weight of the dried trees. This measurement provides data on the growth of the seedlings under different light conditions.
Understanding response variables is key to interpreting an experiment's results. It tells researchers how or if the explanatory variable had the intended effect.
  • For a health study, the response might be the rate of recovery or number of symptoms.
  • In academic research, it could be the test scores of students under different teaching techniques.
Ultimately, the response variable provides the evidence needed to draw conclusions from the study.
Treatments
Treatments in an experiment refer to the specific conditions applied to the experimental units, based on different levels of the explanatory variable. In the pine seedling experiment, the treatments consisted of various levels of light exposure: full light, 25% light, and 5% light.
Choosing the right treatments is crucial, as they directly relate to the research question and help show how varying the explanatory variable affects the response.
  • Treatments should be clearly defined and applied consistently.
  • They are often planned to produce a range of conditions or outcomes.
By applying treatments, researchers aim to tease out the effects of the explanatory variable more clearly and determine its relationship with the response variable.

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