SMPA 2151 Lecture Notes - Lecture 10: Dependent And Independent Variables

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emeraldreindeer855

11 Apr 2018

School

GWU

Department

School of Media &Public Affairs

Course

SMPA 2151

Professor

Professor Porter

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Document Summary

We"ve used regression so far to talk mostly about associations and relationships between variables. We can also use regressions to estimate the effects of an experiment -- meaning we can move beyond associations and relationships. We can use regressions to show the effect that x has on y. If we have multiple treatments, we can compare the effectiveness of each treatment. Each treatment is represented with a binary variable, indicating whether people saw/were exposed to that treatment or not. We can then do this with as many treatments as we have. We then regress our dependent variable of interest on the treatment variables. The r code would look like this: modelname

Related Questions

Experimental Review

Below are five hypothetical experimental designs. Your job as a reviewer is to pick one of the experiments and write a detailed summary of what is wrong with the proposed study.

Your review should use vocabulary words that have been discussed in class and address the following questions.

Is the study feasible? Will it actually be possible to conduct the proposed study in a controlled manner that produces meaningful data? If there is more than one variable changing simultaneously, no controls, or no replication, then the study is unlikely to produce meaningful data. If there is no way to monitor an experiment in the environment, or no way to conduct the experiment in a controlled environment, like a laboratory, then the experiment is unlikely feasible.

Can you tell from the text if the experiment is designed to be conducted by performing treatments, or by analyzing observational data about a species and its habitat?

Is there a testable hypothesis? Is the study set up so that it will be possible to measure the effects in a quantifiable way? What will be measured? Is there a control group and a treatment group? Or, an independent variable like temperature, and a dependent variable like germination time?

Could you graph the results of this experiment? If so, how would you do it? A column chart to show treatments and controls? A scatter plot or a line graph to look at how changes in the independent variable affect the dependent variable?

Create a post on the discussion board by clicking on "Click to Launch" above.

1. Experiments to Review

1. Climate Change Effects on Marine Iguana Mortality

Hypothesis: If the water temperature in the Galapagos Islands changed from being hot (around 77 degrees) to cold (under 70 degrees), then the mortality rate of Marine Iguanas will increase.

Variables: The independent variable is the temperature of the water that the Marine Iguanas live in. The dependent variable is the mortality rate of the Marine Iguanas. The mortality rate of the Marine Iguanas at the average water temperatures of their habitat.

Experimental Treatments: Iguana Group 1 will be water temperatures and marine iguana mortality rates before 1998. Iguana Group 2 will be water temperatures marine iguana mortality rates after 1998

Prediction:By comparting the average water temperatures with the mortality rates every year before the sudden drop in the iguana population and after a trend will be able to be seen. If the water temperature is truly to blame for the mortality rate increase the water temperature will decrease as the population of Iguanas decreases. The control group is intended to show the average number of Iguanas that die due to other causes.

2. Volcanic Ash Impacts Marine Iguana Longevity

Hypothesis: There are several volcanoes between both the Isabela, and Femandina islands which make this the obvious culprit for the extreme rise in mortality in Marine Iguanas.

Variables: The independent variable is the number of volcanic eruptions per year. The dependent variables are the change in pH of the water in the marine iguanasâ habitat, and the mortality rate of the iguanas.

Experimental Treatments: Iguana Group 1 will live on an island with multiple volcanic eruptions each year. Iguana Group 2 will live on an island with no volcanic eruptions.

Prediction: The group of iguanas living on the island with no eruptions will have longer life spans because the pH of the water will not be altered by the large number of volcanic eruptions.

roseclam804

Case Study The USDA conducted a series of experiments to determine the effect of European Corn Borer (ECB) infestation on the yields of four different varieties of corn â Golden Crop and Super Crop, and their genetically modified derivatives GC- 110 and SC-113. The genetically modified organisms (GMO) were engineered to be insect-resistant. Each corn plant produces a single ear of corn, with the number of kernels per ear depending on growth conditions [Fig 1]. Many problems, including insect infestation [Fig 2], plant disease, extreme weather conditions, or poor soil conditions, can decrease kernel yield. For the purpose of the USDA investigation, yield is defined as the kernel weight per ear of corn. All corn plants in this study were grown under the same environmental conditions (ie, soil type, water amount and sunlight exposure); however, the level of ECB infestation was varied. The results of the investigation are given in Table 1.

Questions

Question 1

Which of the following statements best expresses the scientific question addressed by the USDA investigation (see attached file)? [2 pt; L2; I.A.1]

		How destructive is the ECB on four common corn varieties?
		How effective are GMO corn varieties in reducing the loss of yield to ECB infestation?
		What effect does GMO corn varieties have on the growth and development of ECB larvae?
		Are GMO corn varieties more resistant to ECB infestation than non-modified corn varieties?

2 points

Question 2

In the USDA investigation, what were the independent variables? Select all that apply â partial credit is not awarded! [2 pt; L2; I.A.2]

		The variety of corn plant used in the experiment.
		The number of plants tested in each treatment.
		The yield of kernels per ear of corn.
		The level of ECB infestation.

2 points

Question 3

In the USDA investigation, what was the dependent variable? [2 pt; L2; I.A.2]

		The level of ECB infestation.
		The yield of kernels per ear of corn.
		The number of plants tested in each treatment.
		The type of soil and amounts of water and sunlight the plants received.

2 points

Question 4

In the USDA investigation, which of the following were controlled variables? Select all that apply â partial credit is not awarded! [2 pt; L2; I.A.2]

		The type of soil in which the plants are grown.
		The amount of water each plant received.
		The yield of kernels per ear of corn.
		The level of ECB infestation.

2 points

Question 5

In the USDA investigation, what was the negative control? [2 pt; L2; I.A.2]

		Corn plants that were grown in the dark.
		Corn plants that were not exposed to ECB infestation.
		Corn plants that were grown with all-purpose plant food.
		Corn plants that were genetically modified to prevent flowering.

2 points

Question 6

In the USDA investigation, what were the levels of treatment? [2 pt; L2; I.A.2]

		amounts of sunlight and water provided to the plants
		number of ears produced per plant
		amount of food given to the plants
		low and high ECB infestation

SMPA 2151 Lecture Notes - Lecture 10: Dependent And Independent Variables

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