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What is a variable?
Any attribute of objects, people or events that, within the context of the investigation, can take on different values
What is the opposite of a variable?
- A constant
- Any attribute of objects that, within the context of the investigation, possess a fixed value
What is a quantitive variable?
- Variables with numerical values
- Some form of measuring instrument has been employed
- Basically interval data
What are categorical (or nominal) variables?
The name or symbol that designates the category to which a particular object, person or event belongs
What arithmetic is employed for categorical variables?
- The number within each category is counted
- Numbers could also be used as category labels, however
What are discrete variables?
- A subdivision of quantitative variables
- Only takes certain possible integer values such as numbers of heads in 3 coin tosses
What are continuous variables?
- A variable with an infinite number of possible values within a range of measurement
- It is always possible in theory to find a midpoint between values
- The possible value is limited by the precision of measuring instrument used
What is a predictor variable?
- The variable that serves as the basis for protecting values of the response variable
- Also known as the explanatory or independent variable
- May be categorical or quantitative
- If it is categorical, the prediction rule only applies to those values of the predictor variables used in the study
- If the variable is quantitative, the results can be used to make predictions of responses for intermediate values of predictors not used
What is a response variable?
- The variable which values are being predicted.
- We attempt to explain and account for its variability
- Often called the dependent variable
What is a correlational design?
When there is no clear distinction between predictor and response variables
In which ways can variability be studied?
- Natural observation
- Experimental observation
What are the conditions of experimental observation?
The experimenter has complete control over the variable and the assignment of participants to conditions
What are the conditions of natural observations?
The experimenter does not have complete control over the variable and manipulates it through a process of selection
What is a true experiment?
- The combination of a manipulated variable and random assignment
- It is argued that this method can suggest causality
What is a quasi experiment?
- The combination of a natural variable and selection
- It is argued that this method can only show correlation
What does effective data analysis depend on?
- Sound experimental design
- Good stats analysis cannot rescue results from a bad experimental design
What are the two broad goals of experimental design?
- To eliminate bias
- To ensure adequate precision
What is bias?
The tendency for values to differ systematically from their true values
What is precision?
- The amount of random variability in measurement
- The less variability, the greater the precision
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