4. Inferential statistics
Data taken from a sample is
used to estimate a population
parameter
Hypothesis testing (P-values)
Point estimation (Confidence
intervals)
5. POINT ESTIMATE
Estimate obtained from a sample
Inference about the population
Point estimate is only as good as the
sample it represents
Random samples from the
population - Point estimates likely to
vary
10. CONFIDENCE LIMITS
Two extreme measurements
within which an observation
lies
End points of the confidence
interval
Larger confidence – Wider
11. A point estimate is a single
number
A confidence interval contains a
certain set of possible values of
the parameter
Point Estimate
Lower
Confidence
Limit
Upper
Confidenc
e
Limit
Width of
confidenceinterval
20. FACTORS – TO SET CI
Size of sample
Variability of population
Precision of values
21. SAMPLE SIZE
Central Limit Theorem
“Irrespective of the shape of the
underlying distribution, sample mean &
proportions will approximate normal
distributions if the sample size is
sufficiently large”
Large sample – Narrow CI
42. Margin of error
Increase the sample size
Reduce confidence level
Dynamic relation
Confidence intervals and
sample size
43. EXAMPLE
Series of 5 trials
Equal duration
Different sample sizes
To determine whether a novel
hypolipidaemic agent is better than
placebo in preventing stroke
44. Smallest trial 8 patients
Largest trial 2000 patients
½ of the patients in each trial – New drug
All trials - Relative risk reduction by 50%
45.
46. QUESTION
S
In each individual trial, how
confident can we be regarding
the relative risk reduction
Which trials would lead you to
recommend the treatment
unequivocally to your patients
47. MORE CONFIDENT - LARGER
TRIALS
CI - Range within
which the true effect
of test drug might
plausibly lie in the
given trial data
66. EXAMPL
E
Study on a diagnostic test
100% sensitivity when the test is
performed for 20 patients who have
the disease.
Test identified all 20 with the
disease as positive – 100%
No falsely negatives – 0%