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Unformatted text preview: Chapter 6 – Conducting a Good Experiment I: Variables and Control The Nature of Variables o Variables o A v ariable is an event or behavior that can assume at least two values. Another word for value is levels/groups/conditions o Operational definition Bridgman (1927) suggested that researchers should define their variables in terms of the operations needed to produce them. Such definitions allow others to replicate your research Independent Variables o Independent variables (IV’s) – variables that the experimenter purposely manipulates. o Physiological IV Conditions that alters or change the biological state of the participant Examples: Drugs, temperature, sleep deprivation, etc. o Experience Manipulation of the amount or type of training or learning Examples: reinforcement vs punishment/ o Stimulus or environmental IV An aspect of the environment that the experimenter manipulates Participant Characteristics o Participant characteristics : o Aspect of the participant, such as age, sex or personality traits, that are treated as if they are IV’s. o They are not True IV’s because they cannot be manipulated by the experimenter (They are a classification) Dependent Variables – changes as a function of the level of the IV experienced by the participant. • A good DV is valid (it measures what the experimental hypothesis says it should measure) and reliable (producing consistent measurements) o Types of Dependent Variables (DV) o Correctness Correct vs. incorrect (look at number of correctly remembered words) o Rate or frequency Rate of responding: how quickly does Ss respond in a certain time period. (in a 5 min period the rat hit the bar 60 times per min) Frequency : the number of responses or events that occur within a specific time period (number of times children interact during free play) o Degree or amount Single number (level of life satisfaction; self esteem score) o Latency or duration Latency : how quickly did the Ss make response (.15 sec to respond to image on screen) Duration : how long did their response last? (Held key down for 30 sec) Nuisance Variables o Nuisance variables o Unwanted variables that can cause the variability of scores within groups to increase o Nuisance variables increase the spread of scores within a distribution; they do not cause a distribution to change its location. o Unwanted variables that can cause the variability of scores within groups to increase (they do not cause a distribution to change its location) o Examples (indicate the nuisance variable and its effect) o An experimenter measures reaction time in participants ranging from 12- 78 o The ability of participants to recall a list of words is being studied in a room with a noisy elevator o The lab where the participants are tested for manual dexterity has frequent, unpredictable changes in temperature Extraneous Variables (Confounders) o Difference between groups can cause the distributions to be closer together or...
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- Spring '11
- external validity, internal validity, participants