Transcript 10/20/2015

Psychology 202a
Advanced Psychological
Statistics
October 20, 2015
Effect sizes
• Not necessarily standardized.
• Evil journal editors.
• Standardized effect sizes corresponding to
one-sample tests.
d = (M – m0 ) / s
• Effect sizes for differences between means.
d = (M1 – M2) / sP
• What’s large? What’s small? It depends.
Confidence intervals
• Goal: to find a range of reasonable values
for a parameter based on a statistic and its
sampling distribution.
• Question: what null hypotheses would I not
reject on the basis of these data?
• The 100 * (1-a) % CI for the mean:
M ± t critical × s M
Things the 95% confidence
interval doesn't mean
• There is a 95% probability that m is between
(lower bound) and (upper bound).
• I am 95% certain (or confident) that m is
between (lower bound) and (upper bound).
• There is a 95% chance that the interval
(lower bound) to (upper bound) contains m.
• If I conduct confidence intervals in this way,
95% of the time, m will be between (lower
bound) and (upper bound)
Things the 95% confidence
interval does mean
• There is a 95% chance that the confidence
interval resulting from the sample I am about to
take will contain m.
• If I conduct intervals in this way, 95% of the time,
whatever interval I get will contain m.
• Therefore, it is reasonable to act as if this interval
contains m...
• ...because if I do so, in the long run, I will act
correctly 95% of the time.
• Confidence intervals and duck-hunting
statisticians.