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Statistical planning and Sample size determination

Statistical planning and Sample size determination. Planning. Which variables will I collect and how will they be measured? What types of data do they represent? What do I want to do? Describe, compare groups, predict change in Y following change in X?

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Statistical planning and Sample size determination

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  1. Statistical planning and Sample size determination

  2. Planning • Which variables will I collect and how will they be measured? • What types of data do they represent? • What do I want to do? Describe, compare groups, predict change in Y following change in X? • How large a sample do I need to find a clinically important difference statistically significant???

  3. Dummy analysis • How will I describe my data? • What hypothesis tests will I be doing?

  4. Sample size

  5. Descriptive study • Here the sample size will determine the precision of the study (the confidence interval) • Small study>>>> wide CI • Large study>>>>narrow CI • Here power and P values are not relevant

  6. Mean 120 mmHg Sd 20 mmHg What sample size needed for CI to be ± 2.2

  7. Hypothesis testing • Studies where we test hypothesis eg compare groups regarding means or proportions or test significance of correlation or regression coefficients

  8. Type 1 and 2 error

  9. Method 1 • Working with standardised difference and nomogram Method 2Working with 2 means and Sd or working with two proportions

  10. N=130 One tailed table (must X 2)

  11. Use same nomogram N=3000 in total

  12. Examples

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