ESTIMATION OF SAMPLE SIZE AND POWER ANALYSIS FOR CLINICAL RESEARCH STUDIES

1
ESTIMATION OF SAMPLE SIZE AND POWER
ANALYSIS FOR CLINICAL RESEARCH STUDIES
An Academic presentation by Dr. Nancy Agens,
Head, Technical Operations, Pepgra
Group www.pepgra.com Email pepgrahealthcare_at_gmai
l.com
2
Today's Discussion
In Brief Clinical Research and Sample Size
Statistical Analysis Power Analysis and Sample
Size Estimation Sample Size Calculation Maximize
the Power with Minimum Sample Size Sample Size
Calculation Should be done before during or after
the Study Conclusion
OUTLINE
3
In Brief
Clinical research studies the effect of an
intervention on a specific population or the
causation-association between a predicting
variable and a health condition. The results of
these studies are analysed by scientific
statistical methods and statistical significance
is determined. Starting with an adequate sample
size is an important prerequisite to obtain
accurate results and outcomes as determined
statistically. Power analysis is widely
recommended as a method for estimation of
adequate sample size. Contd..
4
Scientific Statistical Methods
5
Clinical Research and Sample Size
Clinical research services involves studying the
effect of an intervention on a specific group of
people with the condition under study.
Selection of inadequate sample size influences on
the final outcomes and is an important
determinant of the appropriateness of the
methodology and Clinical study design. If sample
size is too small, it may fail to detect
significant associations and if sample size is
too large, the time, energy, and money required
for the study is unnecessarily increased. Contd..
6
Statistical analysis planning for clinical trial
involves use of power analysis for estimating
desired sample size in a research study.
Scientific medical writing services provide
sample size calculations and power analysis
support in the process of study designing.
7
Statistical Analysis
Every research study begins with a hypothesis or
an assumption called the null hypothesis or the
research question.
Power analysis is done to estimate the required
sample size to prove or disprove the null
hypothesis or research question. During
statistically analysis, two types of errors are
possible. Type I error occurs when the null
hypothesis is rejected incorrectly while type II
error occurs when the null hypothesis is
accepted incorrectly. Contd..
8
Types of Errors
9
Power Analysis and Sample Size Estimation
1. Hypothesis - The research question is
formulated in the form of the null hypothesis
and alternate hypothesis.
2. Effect size - If the association between the
variable under study and the outcome is strong,
then a smaller sample size can pick up the
association.

• Level of statistics significance The
  researcher along with the statistician should
  establish the acceptable probability of making
  type I error (a)and type II error (ß).
• Power Power refers to the sample size required
  to avoid type II error and probability to avoid
  this error is the statistical power of the
  study.
• Contd..

10
Power Analysis
11
Sample Size Calculation
The above four factors are used to calculate the
sample size along with the null and alternate
hypothesis and the statistical test chosen.
Statistically analysis is then carried out by the
statistician using standard textbooks or
computer software programs. Medical writing
companies provide power analysis and sample size
estimation support.
12
Maximizing Power with Minimum Sample Size
The sample size calculated should be a practical
number and feasible for the clinical research
study.
In cohort studies, taking two measurements, one
at the beginning and the other at the end of the
study can be used for sample size
calculation. Studying few precise variables with
same or similar outcome helps to derive
conclusions with a smaller sample size.
13
When to conduct Sample Size Calculation of a
Study
To make any research study worthwhile, efficient,
and cost effective, it is best to design the
study properly with respect to sample type and
sample size.

• This is often based on assumptions made at the
  beginning of the study.
• The research study should be completed unless
  interim results show extremely harmful effects
  on the subjects.

14
Conclusion
Researchers should use power analysis and
statistically analysis support to predetermine
an effective sample size to make the study
worthwhile.
15
Contact Us
UNITED KINGDOM 44- 7424810299 INDIA 91-98843500
06 EMAIL pepgrahealthcare_at_gmail.com