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Which statistical method?

Which statistical method?. How to decide if the correct statistical test was used Al Best, PhD David Sarrett , DMD, MS. What’s the question?. Questions are of the form: For ___ response variable, is there a relationship with ___ predictor variable?

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Which statistical method?

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  1. Which statistical method? How to decide if the correct statistical test was used Al Best, PhD David Sarrett, DMD, MS

  2. What’s the question? • Questions are of the form: • For ___ response variable, is there a relationship with ___ predictor variable? • For ___ response variable, is there a difference between the groups identified by the ___ predictor variable? • Look at the predictor variable first.

  3. Predictor variable: • Quantitative (numeric)continuous or discrete • Qualitativenominal or ordinal • Special casetime to an event

  4. Predictor variable: • Quantitative (numeric)continuous or discrete • Qualitativenominal or ordinal • Special casetime to an event

  5. Predictor variable: • Quantitative (numeric)continuous or discrete • Qualitativenominal or ordinal • Special case:time to an event

  6. What’s the question? • Questions are of the form: • For ___ response variable, is there a relationship with ___ predictor variable? • For ___ response variable, is there a difference between the groups identified by the ___ predictor variable? • Now look at the outcome variable next.

  7. Response variable: • Quantitative (numeric)continuous or discrete • Qualitativenominal or ordinal

  8. Continuous predictor,Continuous response: • Q: is there a correlation between two numeric variables? • CorrelationSimple linear regression

  9. Continuous predictor,Nominal response: • Q: Does probability of the response change across the numeric predictor? • Logistic regression(which yields a chi-square statistic)

  10. Nominal predictor (independent groups),Continuous response: • Q: is there a mean difference between the groups? • For two groups: a t-test • For more than two groups: ANOVA • Followed by a multiple comparison procedure.

  11. Nominal predictor (independent groups),Nominal response: • Q: is there an association between two nominal variables? • Q: is the % on one variable different across the groups of the other variable? • Chi-square, orFisher’s exact p-value

  12. Nominal predictor (paired occasions or measures),Nominal response: • Q: is there a mean change across time? • Q: is there a difference between two paired measures? • Two: paired t-test • More than two: repeated-measuresANOVA

  13. Nominal predictor (paired occasions or measures),Nominal response: • Q: Are paired nominal outcomes different? • McNemar’s chi-square

  14. Time to an event: A response occurs (event) at a time point • Q: Is the survival time different between groups? • Kaplan-Meier survival analysis • Example: do crowns or amalgams last longer?

  15. What’s the question? • Usually, questions are of the form: • For ___ response variable, is there a relationship with ___ predictor variable? • For ___ response variable, is there a difference between the groups identified by the ___ predictor variable? • Sometimes, you want to conclude “no difference” or “just as good as”. • These require different tests: Equivalence tests.

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