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Inferential Statistics

             Objective:
An introduction to what you need to
        know about statistics
Key Terms
Test statistic
Critical value
Degrees of freedom
P value/level
Significance
Chance
Type 1 error
Type 2 error
Interval
Ordinal
Nominal
Inferential Statistics Tests



    Make inferences about the
populations from which the samples
             are drawn
Descriptive Statistics vs. Inferential Statistics


    Allows us to draw
                          Allow us to say whether
       conclusions
                          difference is significant
  Through use of graphs




                                   This difference
                                    Is significant
Probability
Inferential tests use probability to ascertain the
likelihood that a pattern of results could have
arisen by chance.

If the probability of the results occurring by
chance is below a certain level we assume these
results to be significant
Chance




We can state how certain
we are the results are not      Real
     due to chance           difference
P-levels/Significance Levels


                 P ≤0.10
      C
      H          P ≤0.05
      A
      N          P ≤0.01
      C
      E          P ≤0.001


   We can also write these as 10%, 5%, 1%, 0.1%
Significant?
If our test is significant we can
Reject our null hypothesis and accept our
alternative/experimental hypothesis

If our test is not significant we can
Accept our null hypothesis and reject our
alternative/experimental hyp
Levels of measurement
       Nominal

        Ordinal

       Interval
Levels of data: nominal
• Which newspaper paper do you read
  regularly?




• We can put these into categories.
Levels of Data: ordinal
• What grade did you get for each of your
  gcse’s?




• These can be put in order… highest to lowest
Levels of data: interval
• How quick is your reaction time?




• We can measure and compare the exact time
  because the intervals on the ruler are equal.
Inferential Tests
Which test to use depends upon a number of
factors:
• The type of data
• Type of research design (RM vs. IG)
• One tailed or two tailed test
Tests to Know
Mann Whitney U
 Chi Squared
  Wilcoxon T
Spearmans rho
Process



data
                                Complicated arithmetic




       Produce test statistic
Sig levels ½’d for one
                                                                tailed test




       Compare test
          Statistic
     with critical values
        for that test
 To determine significance
            level




critical value: Value that test statistic must reach in order for null hyp to be rejected
Sig levels ½’d for one
      tailed test
Type 1 and Type 2 Errors
Type 1 error

Rejecting a null hypothesis when we should not
                 P level too tight




                           Type 2 error

                           Accepting a null hypothesis when we should not
                                           P level too loose

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Inferential statistics powerpoint

  • 1. Inferential Statistics Objective: An introduction to what you need to know about statistics
  • 2. Key Terms Test statistic Critical value Degrees of freedom P value/level Significance Chance Type 1 error Type 2 error Interval Ordinal Nominal
  • 3. Inferential Statistics Tests Make inferences about the populations from which the samples are drawn
  • 4. Descriptive Statistics vs. Inferential Statistics Allows us to draw Allow us to say whether conclusions difference is significant Through use of graphs This difference Is significant
  • 5. Probability Inferential tests use probability to ascertain the likelihood that a pattern of results could have arisen by chance. If the probability of the results occurring by chance is below a certain level we assume these results to be significant
  • 6. Chance We can state how certain we are the results are not Real due to chance difference
  • 7. P-levels/Significance Levels P ≤0.10 C H P ≤0.05 A N P ≤0.01 C E P ≤0.001 We can also write these as 10%, 5%, 1%, 0.1%
  • 8. Significant? If our test is significant we can Reject our null hypothesis and accept our alternative/experimental hypothesis If our test is not significant we can Accept our null hypothesis and reject our alternative/experimental hyp
  • 9. Levels of measurement Nominal Ordinal Interval
  • 10. Levels of data: nominal • Which newspaper paper do you read regularly? • We can put these into categories.
  • 11. Levels of Data: ordinal • What grade did you get for each of your gcse’s? • These can be put in order… highest to lowest
  • 12. Levels of data: interval • How quick is your reaction time? • We can measure and compare the exact time because the intervals on the ruler are equal.
  • 13. Inferential Tests Which test to use depends upon a number of factors: • The type of data • Type of research design (RM vs. IG) • One tailed or two tailed test
  • 14. Tests to Know Mann Whitney U Chi Squared Wilcoxon T Spearmans rho
  • 15. Process data Complicated arithmetic Produce test statistic
  • 16. Sig levels ½’d for one tailed test Compare test Statistic with critical values for that test To determine significance level critical value: Value that test statistic must reach in order for null hyp to be rejected
  • 17. Sig levels ½’d for one tailed test
  • 18. Type 1 and Type 2 Errors Type 1 error Rejecting a null hypothesis when we should not P level too tight Type 2 error Accepting a null hypothesis when we should not P level too loose