statistical planning and sample size determination
TRANSCRIPT
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Statistical planning Statistical planning and Sample size and Sample size determinationdetermination
Statistical planning Statistical planning and Sample size and Sample size determinationdetermination
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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???
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Dummy analysis• How will I describe my data?
• What hypothesis tests will I be doing?
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Sample size
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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
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Mean 120 mmHg Sd 20 mmHg What sample size needed for CI to be ± 2.2
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Hypothesis testing• Studies where we test hypothesis
eg compare groups regarding means or proportions or test significance of correlation or regression coefficients
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Type 1 and 2 error
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Method 1• Working with standardised
difference and nomogram
Method 2Working with 2 means and Sd or
working with two proportions
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N=130
One tailed table (must X 2)
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• Use same nomogram
N=3000 in total
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Examples