Experimental Exam 2
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. What would you like to do?
- to describe the characteristics or behaviors of a given population in a systematic and accurate fashion
- usually a survey
- on from which we can draw accurate, unbiased estimates of the characteristics of the larger population
- we can draw accurate inferences about the population from data obtained from a sample only if it is representative
causes results obtained from the sample to differ from what would have been obtained had the entire population been studied
margin of error:
indicateds the degree to which the data obtained from the sample are expected to deviate from the population as a whole
simple random sampling:
- every possible sample of the desired size has the same chance of being selected from the population
- ex) we want to select a sample of 200 PPTs from a school district that has 5000 students; if we wanted a simple random sample we would select our sample in such a way that every possible combination of 200 students has the same probability of being chosen
stratified random sampling:
- a variation of random sampling
- rather than selecting cases directly from the population, we first divide the population into two or more strata
- ex) the researcher might want to compare younger respondents to older respondents; first stratifying the sample, the researcher ensure that there will be an ample number of both young and old respondents in the sample
- researchers use whatever participants are readily available
- ex) sona, most of the psychology studies
What are the 3 measures of central tendency?
what is correlation coefficient?
a statistic that indicates the degree to which two variables are related to one another in a linear fashion
what is the numerical range for correlation coefficient?
-1 to +1
What 2 pieces of information are communicated in the correlation coefficient?
- positive or negative relationship
- strength of relationship
coefficient of determination:
- the square of the correlation coefficient
- indicates the proportion of variance in one variable that can be accounted for by the other variable
- a set of data in which PPTs scores are confined to a narrow range of the possible scores
- correlations with restricted range are smaller
- scores that are so obviously deviant from the remainder of the data that one can question whether they belong in the data set at all
- they can lead to erroneous conclusions about the strength of the correlation b/w variables
What are the three characteristics that define an experiment?
- 1) manipulation of IV
- 2) random assignment - researcher must have the power to assign participants to the various experimental conditions in a way to assure their initial equivalence
- 3) control for confounds
what are 3 types of IVs (manipulation)?
- environmental manipulations: involve experimental modification of the participants' physical or social environment
- instructional manipulations: vary the variable through verbal instructions that participants reeive
- invasive manipulations: involve creating physical chnages in the participant's body through surgery or the administration of drugs
a question that is designed to determine whether the IV was manipulated successfully
simple random assignment:
- random assignment of participants to groups
- most basic and important control procedure
- every participant has an equal probability of being placed in any condition
- important because it is a powerful control procedure b/c accounts for all unwanted subject variables
taking a random group from a larger group
randomly splitting the sample into groups
matched random assignment:
a procedure for assigning participants to experimental conditions in which participants are first matched into homegeneous blocks and then participants within each block are assigned randomly to conditions
- participants assigned to on group (random or matched assignment)
- compare differences in behavior b/w different groups
- single group of participants exposed to ever IV level
- eliminated the need for random assignment
- 100% sure that PPTs in each group dont differ
What are the stregths of within-subject design?
- controls for individual differences
- few PPTs are needed
- Instructions may take less time
What are the weaknesses of within-subject design?
- order effects
- b/c ppts experience all conditions, is easier to figure out the hypothesis
present every possible order
choose limited number of orders at random
latin square design:
each condition appears once at each ordianl position
the degree to which a researcher draws accurate conclusions about the effects of the independent variable
the loss of ppts during a study
experimenter expectancy effects:
a situation in which a researchers expectations about the outcome of a study influences ppts reactions
aspects of a study that indicate to ppts how they are expected to respond
neither the ppts nor the experimenters who interact with them know which experimental condition a ppt is in at the time the study is conducted
the degree to which the results obtained in one study can be replicated or generalized to other samples, research settings, and procedures
problems with correlational research:
- restricted range
- reliability of measure
problems with causality:
- reverse causality
- means your sample is accurate of the population
- allows accurate, unbiased estimates
consistency of measures
realism to outside world
what is the best way to increase significance?
increase the sample size
a list of the members of a population
error of estimation
the degree to which data obtained from a sample are expected to deviate from the population as a whole
most correlational research satisfies what criteria for determining causality?
an accomplis of an experimenter whom participants assume to be another participant or bystander
one level of an IV
a condition that exists in experimental research when something other than the IV differs systematically among the experimental conditions
What would you like to do?
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