Reasoning in Psychology Using Statistics

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Reasoning in PsychologyUsing Statistics

• Psychology 138
• 2015

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Exam 3 review Inferential Statistics

• Distribution of sample means
• Standard error
• Central limit theorem
• Hypothesis testing

• Test statistics
• 1-sample z
• 1-sample t
• Related sample t
• Independent sample t

• 5 step program
• Hypotheses
• Null and Alternative
• 1 or 2 tailed
• Error types
• p(Type I error) a alpha
• p(Type II error) ß beta
• Reaching a conclusion
• Reject the H0
• Fail to reject H0

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Inferential statistics

• Hypothesis testing
• Testing claims about populations (and the effect
  of variables) based on data collected from
  samples
• Using estimates of the sampling error (expected
  difference between the sample statistics and the
  population parameters)

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Properties of the distribution of sample means
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Properties of the distribution of sample means
Standard error
the average amount a
sample mean (of a particular sample size) will
differ from the population mean.
Used as our difference expected by chance in our
test statistics.
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Properties of the distribution of sample means
Standard error
the average amount a
sample mean (of a particular sample size) will
differ from the population mean.
Used as our difference expected by chance in our
test statistics.
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Performing your inferential statistics

• Analyze the question/problem.
• The design of the research how many groups, how
  many scores per person, is the population s
  known, etc.

• Write out what information is given
• Means, standard deviations, number of subjects,
  a-level, etc.
• Is it asking you to test a difference or make an
  estimate?
• If hypothesis test
• What are the H0 and HA?
• 1-tailed or 2-tailed hypotheses?
• What is your critical value of your test
  statistic (z or t from table, youll need youre
  a-level)

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Performing your inferential statistics

• Analyze the question/problem.

• Now you are ready to do some computations
• Write out all of the formulas that youll need

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Performing your inferential statistics

• Analyze the question/problem.
• Now you are ready to do some computations

• Draw a Conclusion and Interpret your final answer

• Reject or fail to reject the null hypothesis?

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Performing your inferential statistics

• Analyze the question/problem.
• Now you are ready to do some computations

• Draw a Conclusion and Interpret your final answer

• Reject or fail to reject the null hypothesis?

Distribution of the t-statistic or z-statistic
Evidence suggests that the treatment has an
effect
Evidence suggests that the treatment has no
effect
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Hypothesis testing formulas summary
(Estimated) Standard error
df
Design
Test statistic
One sample, s known
One sample, s unknown
Two related samples, s unknown
Two independent samples, s unknown
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How do I study for this test?

• The usual
• Review lecture notes and labs
• Re-read the Reading packet
• Do practice problems
• Remember to ask yourself conceptual questions
  
• e.g., What would happen to my standard error
  if I increased my sample size?
• Make Flash Cards of problems

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Make your flash cards

• Dr. Mnemonic develops a new treatment for
  patients with a memory disorder. He isnt
  certain what impact, if any, it will have. To
  test it he randomly assigns 8 patients to one of
  two samples. He then gives one sample (A) the
  new treatment but not the other (B) and then
  tests both groups with a memory test. Use a
  0.05.

Independent samples t-test
Two tailed any impact
Fail to Reject H0
Evidence suggests that the treatment has no effect
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Make your flash cards
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Make your flash cards

• Dr. Psychic examined the performance of 28
  students who answered multiple-choice items on
  the SAT test without having read the passages to
  which the items referred. The mean score was
  46.6 (out of 100), with a standard deviation of
  6.8. Test whether these students performed
  different than chance (chance performance would
  result in 20 correct scores) with an a-level
  0.01.

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In labs

• Practice determining which statistical test is
  appropriate for a number of different situations,
  and carrying out that test (practice by hand and
  using SPSS).