CRIM 220 Chapter Notes - Chapter 7: Design Of Experiments, Random Assignment, Statistical Hypothesis Testing

98 views4 pages

ivoryfrog449

12 Feb 2018

School

Simon Fraser University

Department

Criminology

Course

CRIM 220

Professor

Ted Palys

For unlimited access to Textbook Notes, a Class+ subscription is required.

Document Summary

Experimentation is an approach to research best suited for explanation and evaluation: experimentation is best suited for hypothesis testing in explanatory research or evaluation studies. Variables, time order, measures and groups are the central features of the classical experiment: defining feature of an experiment lies in the control of the independent variable by the experimenter. Pretesting and posttesting: general problem that plagues forms of cj research: studying something may change it. Double blind experiments: neither subjects nor the experimenters know which is the experimental group and which is the control. Random assignment: random assignment is a central feature of the classical experiment, most important characteristic is that it produces experimental and control groups that are statistically equivalent. Experiments and threats to internal validity: problem of threats to internal validity refers to the possibility that conclusions drawn from experimental results may not accurately reflect what went on in the experiment itself.

Related Questions

You and your hypothetical lab partner each develop an experimental plan to test this hypothesis. The two experimental plans are presented below. Evaluate each plan for its pros and cons in the experimental design using the bullet points below. Both experimental plans have some good elements and areas that could be improved.

Experiment A) Mature 2 inch sections (sprigs) of Elodea will be used to measure oxygen production under different light conditions. 5 sprigs will be tested. One will be kept in the dark (no light). The others will be exposed to a light filtered with cellophane. One sprigâs light will be filtered through clear cellophane to receive all wavelengths of light, and the other sprigsâ light will be filtered through red, blue, and green cellophane, respectively. The no-light plant will be kept in a dark cabinet, while the other plants will be together on a counter. Each plant sprig will be placed in equal sized upside-down test tubes in 100ml of tap water so that oxygen bubbles produced by the plant will be trapped at the top of the test tube. A ruler will be used to measure the length of the oxygen pocket collected at the top of the test tube. The experiment will continue until one sprig produces 5 cm of oxygen in the tube.

Experiment B) 3 cm sections (sprigs) of Elodea of various ages will be used to measure oxygen production under different light conditions. 15 sprigs will be divided into 3 groups of 5 sprigs each. One group will receive natural sunlight, one group will be exposed to a blue light bulb under a box to block natural light, and the final group will be exposed to a red light bulb under a similar box to block natural light. Each group of plant sprigs will be trapped under a clear plastic funnel that is covered by an upside-down test tube to collect oxygen bubbles produced by all the sprigs in the group. All groups will be in 100ml of water of the same temperature and pH. The experiment will continue for 24 hours, and then the volume of oxygen gas produced will be measured by multiplying the length of the oxygen pocket by the circle described by the test tube, ?r². The average volume produced by all groups will be graphed and compared to determine which condition produced the most total volume of oxygen.

Consider the following questions to evaluate experimental plans A and B (DO NOT ANSWER THESE QESTIONS)

What is the independent variable suggested by the hypothesis? Do both plans test the independent variable equally well?

What is the dependent variable in each experiment? Which experimentâs dependent variable best matches the prediction in the hypothesis?

What are the experimental and control groups for each experiment? Which experiment gives the best opportunity to assess the effect of the independent variable?

How does each experiment account for standardized variables? Which experiment do you think is the better controlled experiment?

How is sample size addressed in each experiment? Which would you find to be more convincing?

Does either experiment describe any statistical analyses to be performed on the data?

ANSWER THIS QUESTION: BELOW

Considering your analysis of each of the questions above,write an improved experimental design to test the hypothesis âIf blue light is more effective at promoting photosynthesis, then more oxygen gas (O₂) will be produced when plants are exposed to blue-filtered light compared to other wavelengths.âYou may use elements of the above experiments

lilaccod491

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

It refers to some of the Project titles only helpme thank you

QUESTION 1

Student A carried out an experiment to test for the presence of protein in skim milk. He used a chemical indicator called Biuret reagent which turns purple in the presence of proteins (the reagent is blue). He also identified egg white as an example of a solution containing protein and verified that egg white does cause the Biuret reagent to turn purple. For his milk experiment, Student A added the following items to a test tube and heated it for 3 minutes: 1 mL skim milk, 1 mL distilled water, 0.5 mL of egg white, 0.5 mL Biuret reagent. The solution turned purple and the student concluded that the milk contained protein.

What is the function of the egg white?

		it is the negative control
		it is the experimental group
		egg white serves no purpose in this experiment
		it is a positive control

0.66 points

QUESTION 2

You've just read a research project titled: "The activity of alcohol dehydrogenase enzyme is affected by pH."

What is the control?

	A.	pH = 1
	B.	temperature
	C.	zero pH
	D.	the type of alcohol used
	E.	neutral pH

0.67 points

QUESTION 3

You've just read a research project titled: "Prolonged cell phone use causes brain tumors."

What is the dependent variable?

	A.	number of patients with brain tumors
	B.	medical history of these patients
	C.	length of cell phone use
	D.	age of patients
	E.	type of cell phone used

0.67 points

QUESTION 4

Which of the following would be standardized variables in the "pine trees on hillsides" study? Mark all that apply.

		elevation above sea level
		same lattitude
		counting trees at the same time of year
		similar climate
		angle of the hill slope
		same size area
		same history of logging activity (environmental succession)

0.67 points

QUESTION 5

Which of the following would be standardized variables in the "cell phones cause brain tumors" experiment? Mark all that apply.

		same history of phone use in each group
		same age distribution in each group
		similar medical backgrounds and family histories
		same number of males and females in each group
		same type of phone
		same amount of time on the phone
		holding phone at the same distance and on the same side of the head

0.67 points

QUESTION 6

What is wrong with this experiment? (select the single best answer)

		Student A should not have heated the samples.
		Student A should not have added the distilled water.
		Student A should have used a different test that gives quantitative data.
		Student A combined the milk with a substance known to contain protein in a single tube.

0.67 points

QUESTION 7

You've just read a research project titled: "Pine trees are more numerous on hillsides."

What is the independent variable?

	A.	logging activity
	B.	number of pine trees
	C.	slope of the land
	D.	size of geographic area
	E.	average rainfall

0.67 points

QUESTION 8

You've just read a research project titled: "Prolonged cell phone use causes brain tumors."

What is the independent variable?

	A.	medical history of these patients
	B.	age of patients
	C.	length of cell phone use
	D.	number of patients with brain tumors
	E.	type of cell phone used

0.66 points

QUESTION 9

You've just read a research project titled: "The activity of alcohol dehydrogenase enzyme is affected by pH."

What is the dependent variable?

	A.	pH
	B.	enzyme activity
	C.	substrate concentration
	D.	enzyme concentration
	E.	temperature

0.66 points

QUESTION 10

You've just read a research project titled: "Pine trees are more numerous on hillsides."

What was used as a control?

	A.	average rainfall
	B.	lowland flat environment
	C.	number of pine trees
	D.	area at a different lattitude
	E.	logging activity

0.67 points

QUESTION 11

You've just read a research project titled: "The activity of alcohol dehydrogenase enzyme is affected by pH."

What is the independent variable?

	A.	pH
	B.	substrate concentration
	C.	enzyme activity
	D.	enzyme concentration
	E.	temperature

0.66 points

QUESTION 12

You've just read a research project titled: "Pine trees are more numerous on hillsides."

What is the dependent variable?

	A.	average rainfall
	B.	size of geographic area
	C.	number of pine trees
	D.	logging activity
	E.	environment and elevation

0.66 points

QUESTION 13

Which of the following would be standardized variables in the "alcohol dehydrogenase" study? Mark all that apply.

		type of alcohol used
		type of container used (beaker, flask, or plastic cup)
		pH
		substrate concentration
		temperature
		enzyme concentration
		amount of time to react

0.67 points

QUESTION 14

What should Student A use as a negative control for this experiment?

		1 mL distilled water + 0.5 mL Biuret reagent
		1 mL skim milk + Biuret reagent
		1 mL Biuret reagent + 1 mL distilled water + 1 mL skim milk
		1 mL egg white + Biuret reagent

0.67 points

QUESTION 15

You've just read a research project titled: "Prolonged cell phone use causes brain tumors."

What would be an appropriate control in this experiment?

	A.	a group of patients limited to a small number of short-duration calls per day
	B.	patients with a family history of cancer
	C.	patients that are the same age
	D.	a group of patients that already have brain tumors

fuchsiaoyster134

CRIM 220 Chapter Notes - Chapter 7: Design Of Experiments, Random Assignment, Statistical Hypothesis Testing

Document Summary

Get access

Related Documents

CRIM 220 Chapter Notes - Chapter 7: Causal Inference, Random Assignment, Observational Error

CRIM 220 Chapter Notes - Chapter 7: Statistical Conclusion Validity, Observer-Expectancy Effect, Design Of Experiments

CRIM 220 Lecture Notes - Lecture 4: Internal Validity, Hawthorne Effect, Statistical Conclusion Validity

Related Questions