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Cause-and-effect inferences can be made in an experimental design because a. The researcher manipulates both the independent and dependent variables b. The researcher controls the dependent variable throughout the experiment c. The researcher directly controls or manipulates changes in the independent variable d. Participants are systematically assigned to experimental conditions.

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Related questions

dentifying Dependent and Independent Variables

In order to test a hypothesis and prediction, controlled experiments are used. Controlled experiments involve several necessary components. An independent variable is usually manipulated by a researcher but does not change as a result of the experiment. The changes in the dependent variable may be caused by the experiment (and depend upon the independent variable). Graphs that depict the experimental data list the independent variable on the x-axis while the y-axis shows the dependent variable.

A commonly used mnemonic (memory device) to aid in distinguishing the characteristics of the types of variables is DRY MIX.

D = dependent variable (depends on the other)

R = responding variable (one that changes)

Y = y-axis on a graph

M = manipulated variable (one that is changed by the researcher)

I = independent variable

X = x-axis on a graph

The following sentence is a template to write an if/then statement to be used as a prediction:

If the independent variable is changed [increased, decreased, etc.], then the dependent variable will change in this way [increase, decrease, etc.].

Example: If the amount of available light increases, then plant growth will increase.

Discussion Questions:

Use the tools and examples just discussed to answer the questions about the experiment scenario described next.

Jonah and Tessa noticed that some Leopard frogs by a local river had extra limbs. They decided to check various areas along the river to make more observations. They recorded their observations in their field notebooks. Jonah and Tessa performed a simple laboratory experiment with Leopard frog eggs and river water taken at various spots along the river. They noticed that adult frogs developing from eggs in water collected near an industrial park showed more deformities, but the deformities seemed to be different than those seen on frogs in the natural setting by the river.

Write a prediction that would be appropriate for the experiment scenario.

What would be the independent variable in the experiment?

What would be the dependent variable in the experiment?

What steps should Jonah and Tessa take to ensure that the experiment would be controlled?

Why would they perform these experiments in the laboratory and not in the river?

What conclusion should the researchers derive from their data?

What might be some alternative hypotheses for this situation?

What could be a next step for their investigation?

What other information may help them design future experiments?

1. A study is being done to test the affects of habitat space onthe size of fish populations. Different sized aquariums are set upwith six goldfish in each one. Over a period of six months, thefish are fed the same type and amount of food. The aquariums areequally maintained and cleaned throughout the experiment. Thetemperature of the water is kept constant. At the end of theexperiment the number of surviving fish are surveryed

A. Independent Variable:

B. Dependent Variable:

C. Controlled Variables/Constants:

D. Experimental Controls/ Control Groups:

2. To determine if the type of agar affects bacterial growth, ascientist cultures E. coli on four different types of agar. Fivepetri dishes are set up to collect results:

One with nutrient agar and E. coli
One with mannitol-salt agar and E. coli
One with MacConkey agar and E. coli
One with LB agar and E. coli
One with nutrient agar but NO E. coli

All petri dishes received the same volume of agar, and were thesame shape and size. During the experiment, the temperature atwhich the petri dishes were stored, and at the air quality remainedthe same. After one week the amount of bacterial growth wasmeasured.

A. Independent Variable:

B. Dependent Variable:

C. Controlled Variables/ Constants:

D. Experimental Controls/ Control Groups:

taupecamel909

Psychology

Read the following 2 scenarios and answer each part:

1. A drug company is advertising a new drug that helps people recover from jet lag faster. You are skeptical so you conduct an experiment to test their claim. In your experiment, 100 people are flown from San Francisco to Tokyo. During the flight, half the participants are given the drug companyâs new drug. The other half of the participants are given a placebo (i.e., sugar pill) during the flight. Six hours after they land, all subjects are asked to rate how sleepy and disoriented they feel.

A. Variables (measured/manipulated)

B. Variable levels

C. Research method

D. Research question (descriptive/causal)

E. Operational definitions

2. A manufacturing plant hired an industrial psychologist to determine whether or not lighting conditions make a difference in worker productivity. The study required that employees work under three different levels of illumination during a month-long investigation of worker productivity.

A. Develop a clear research question,

B. Identify variables that might be studiedâi.e., a possible independent variable and dependent variable if the study is experimental, or measured variable(s) if the study is non-experimental,

C. Operationalize the variables.