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# Variables and Hypotheses

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• In class practice on identifying IV and DV for #15
• In class practice on identifying IV and DV for #15
• ### Variables and Hypotheses

1. 1. Variables A variable is any characteristic or condition that can take on different values or “levels” SODA TYPE GENDER ROOM TEMPDiet Coke Diet Pepsi male female 65o 75o 85o 95o Soda Type, Gender, and Room Temperature are all variables because they can take on different values or levels 1
2. 2. Independent Variable (IV) Variable the researcher manipulates or selects for comparison The independent variable is presumed to have an effect on the dependent variableDependent Variable (DV) Variable that is measured The dependent variable is presumed to be affected by the independent variable 2
3. 3. A tip to distinguish IV and DV Frame the question this way: What is the effect of ________ on ________? This will be the IV This will be the DV 3
4. 4. A tip to distinguish IV and DV Example: A psychologist interested in the use of imagery in memory teaches one group of participants to make mental images of things they are trying to remember. She compares their memories for a list of words to the memories of a group that does not receive imagery training. Reframed, it makes sense to ask: What is the effect of imagery training on memory? So imagery training must be the IV and memory must be the DV. 4
5. 5. Extraneous Variables Variables the researcher wants to control so that they do not have an influence on the outcome of the study. For example, if you were conducting a taste test between two sodas, you would want to control: Temperature of the soda so that both are the same How long the soda had been on the shelf The container, so that both look the same Many others! You control extraneous variables so that they don’t impact the effect of the independent variable on the dependent variable. 5
6. 6. Research Hypothesis The researcher’s question and knowledge of existing theory and previous research forms the basis for the research hypothesis The researcher’s prediction about the expected relationship among two or more variables. Example: Reading speed will be faster for text printed in a large font. Tip! In our judicial system, the prosecutor acts much like a researcher. They begin with the research hypothesis that “The person is guilty.” 6
7. 7. Null Hypothesis The statement that there is no relationship among the variables. In statistics, it actually the null that gets tested and the researcher hopes that the results of the statistical test will allow the researcher to reject the null hypothesis. Research Hypothesis: Null Hypothesis: Reading speed will be Reading speed will not be faster for text printed in faster for text printed in a a large font. large font. Tip! In our judicial system, the presumption of innocence is the null hypothesis, “The person is not guilty.” We have to begin with the assumption that this null is true. But the prosecutor (“researcher”) hopes to produce enough evidence to reject this null. 7
8. 8. Null and Research Hypothesis More examplesResearch Hypothesis: Null Hypothesis:Children who are Children who are homehome schooled are schooled are not lessless sociable than sociable than otherother children. children.Research Hypothesis: Null Hypothesis:Men and women differ Men and women doin time spent surfing not differ in time spenton the Internet. surfing on the Internet. 8