Chapter 2.doc

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18 Apr 2012
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Chapter 2: General Principles
Variables
- two types
odependant
outcome variables
measures that constitute the results of the study
variation in them depends on other factors
oindependent
variables under the control of the researcher
object of the study is to find if the independent variables are the related to the
variations in the dependant variable
two ways of creating
through experimental manipulation: creating the variable of change for
ex. Condition 1: sound condition 2: no sound
selection: choosing people for the study who are at the desired levels of
the variables
independent variables are also known as FACTORS and the particular values
that the variables take is referred to as LEVELS
Validity
- did the study measure what it set out to measure
- three forms
oexternal
can we generalize the information to real life situations
table p. 14
oInternal
Independent variable really relates to the dependant variable in the manner
claimed
If there are any other variables that aid to the difference in dependant variable
then there is no internal validity
oconstruct
have we arrived at the correct explanation for the cause and effect relation
if competing explanations for the results for the results cannot be ruled out
then the study lack construct validity
the more tightly controlled the experiment the greater the internal validity and
the worse the external and vice versa for experiments done in natural settings
Sampling
- selection of participants for research
- the hope is that the sample is representative of the POPULATION you can therefore
generalize your findings
- increases external validity
- once the desired population has been defined ex. 3 year olds in Canada …then the next
step is RANDOM SAMPLING
oevery member of the sample has an equal chance of being selected for the research
oif all members are equally likely to be chosen then it is said to be representative of
the population
Stratified sampling
- identify subgroups within the population that they want to be sure are representing in their
correct proportions in the final sample
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