statistical planning and sample size determination
Post on 13-Dec-2015
235 Views
Preview:
TRANSCRIPT
Statistical planning Statistical planning and Sample size and Sample size determinationdetermination
Statistical planning Statistical planning and Sample size and Sample size determinationdetermination
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???
Dummy analysis• How will I describe my data?
• What hypothesis tests will I be doing?
Sample size
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
Mean 120 mmHg Sd 20 mmHg What sample size needed for CI to be ± 2.2
Hypothesis testing• Studies where we test hypothesis
eg compare groups regarding means or proportions or test significance of correlation or regression coefficients
Type 1 and 2 error
Method 1• Working with standardised
difference and nomogram
Method 2Working with 2 means and Sd or
working with two proportions
N=130
One tailed table (must X 2)
• Use same nomogram
N=3000 in total
Examples
top related