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Chapter 13

chapter 13 review


Department
Psychology
Course Code
PSYB01H3
Professor
Connie Boudens
Chapter
13

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Chapter 13 Understand Research Results: Statistical Inference
Infer whether the results that were obtained in a particular study would still
occur if the study were repeated over and over again
SAMPLES AND POPULATIONS
Researchers conduct studies from a single sample of research participants
They rarely conduct studies from entire populations; their findings are based
ons ample data
So with this sample data, you want to be able to make statements about the
entire populations and so, you want ot know if the results will be the same if
the experiment were conducted again with a new sample
Inferential statistics: used to determine whether we can, in fact, make
statements that the results reflect what would happen if we were to conduct
the experiment again and again with multiple samples
Asking if whether we can infer that the difference in the sample means
reflects a true difference in the population means
Inferential statistics allow us to arrive at such conclusions on the basis of
sample data
INFERENTIAL STATISTICS
Importance of ensuring that the groups are equivalent in every way except
the independent variable manipulation
Equivalence of groups are maintained by controlling all other variables or by
randomization
If the groups are equivalent, then you assume that any differences found in
the dependent variable are due to the effect of the independent variable
Differences between any two groups will amost never be zero
oThis means that there will be some difference in the sample means,
even if you manage to carry out the experiment properly
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oThis happens because you are dealing with samples and not
populations
oRandom or chance error will be responsible for some difference in the
means even if the independent variable had no effect on the dependent
variable
oPoint is, the difference in the sample means reflects any true difference
in the population means plus any random error
Inferential statistics allow researchers to make inferences about that true
difference in the population on the basis of the sample data
Inferential statistics give the probability that the difference between means
reflects random error rather than a real difference
NULL AND RESEARCH HYPOTHESES
Statistical inference begins with a statement of the null hypothesis and a
research (or alternative) hypothesis
Null hypothesis: the population means are equal the observied difference
is due to random error
oStates that the independent variable had no effect
Research hypothesis: the populations means are, in fact, not equal
oStates that the independent variable did have an effect
If we can determine that the null hypothesis is incorrect, then we accept the
research hypothesis as correct
Acceptance of the research hypothesis means that the independent variable
had an effect on the dependent variable
With the null hypothesis, we know precisely the probability of the outcome of
the study occurring if the null hypothesis is correct
So we want to infer that the research hypothesis is correct only by rejective
the null hypothesis
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The null hypothesis is rejected when there is a very low probability that the
obtained results could be due to random error
Statistical significance: a significant result is one that has a very low
probability of occurring if the population means are equal
Significance indicates that there is a low probability that the difference
between the obtained sample means was due to random error
Significance is a matter of probability
PROBABILITY AND SAMPLING DISTRIBUTIONS
Probability: the likelihood of the occurrence of some event or outcome
We want to specify the probability that an event (difference between means in
the sample) will occur if there is no difference in the population
If the probability is very low, then we reject the possibility that only random
or chance error is responsible for the obtained difference in means
Probability: The Case of ESP
Your friend claims to have ESP (extrasensory perception) ability
You test your friend with a set of five cards that are used in ESP research a
different symbol is on each card
You look at each card and think about the symbol and yoru friend tells you
which symbol you are thinking about
In the experiment you have 10 trials each of the five cards is shown two
times in a random order
You must know whether your friends answers are random error (guessing) or
if they are more than random error
The null hypothesis is that only random error is occurring, so they are only
guessing
The research hypothesis is that the number of correct answers shows more
than the guessing
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