Experimental Design and Data Analysis, Slides of Experimental Design

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Experimental Design and Data

Analysis

Nilesh B. Patel, PhD

Dept Medical Physiology

University of Nairobi

Kenya

What is science?

• The systemic study of the structure and

behavior of the physical world, involving

experimentation and measurement and

the development of theories to describe

the results of these activities.

• Cambridge International Dictionary of English

What can be studied with the

methods of science?

1. The capital of Kenya is Nairobi.

2. Holland is twice the size of Kenya.

3. All humans are mortal.

4. All rabbits are grey.

5. All ziwats are blue.

6. Mentally ill people are possessed by an evil

spirit.

7. Mentally ill people are possessed by an evil

spirit that cannot be detected by any known

means.

Adapted from: Circadian Physiology. Roberto Refinetti. CRC Press 2000

Galileo Galilei

• Father of modern physics
• Father of modern

observational astronomy

• Father of modern science
• Pioneered the use of

quantitative experiments

whose results could be

analyzed with

mathematical precision

How many of you accept that the sun goes round the earth?

How many of you accept that the earth goes round the sun?

Experimental Design

• Whether or not a study s findings are

useful or not depends crucially on design.

• No matter how ingenious or important an

idea for an experiment might be, if the

study is badly designed, it s worthless.

• The virtue of the experimental method for

doing science is that it is an excellent

procedure for determining cause and

effect.

Three Aims of Research

• Validity

• Results actually show what it is that you intent them to

show

• Reliable

• Potentially replicable by yourself or anyone else

• Important

• Subjective

• Research can possess all the above qualities

but still be essentially trivial.

• Conversely, a research cannot be important if its

findings are unreliable or invalid.

Evidence for the intellectual

inferiority of women

• Paul Broca (

th

Century) make careful

measurement of brain weight and found

Caucasian men have larger brains than

Caucasian women, who in turn have a larger

brain than negros or any other non-Caucasian

for that matter.

• Modern brains were supposedly heavier than

medieval brains, and French brains were heavier

than German brains.

• The brain weights differences were considered

to reflect differences in intelligence between

these different groups.

Experimental Design

• This is important so that the results can be

interpreted and other causes can be

excluded from the most likely conclusion.

• The results have to be valid, reliable and

generalizable (important)

Importance of Control

Measurement

Measurement

Measurement

Measurement Treatment

Experimental

Treatment

Control

Experiment with Control

Importance of randomization

in sample selection

Random allocation

Treatment

Experimental

Treatment

Control

Measurement

Measurement

Measurement

Measurement

Measurement

Measurement Treatment

Experimental

Treatment

Control

Post-test/control group

Independent variable and dependent

variable

Random allocation

Treatment

Level A

Treatment

Control

Measurement

Measurement

Multiple Levels of Independent Variable

Measurement of dependent variable

Measurement

Measurement Measurement

Measurement Treatment

Level C

Treatment

Level B

Measurement

Measurement

Multi-Factorial Design

• Two or three independent variables in the

same study

• Gender and treatment

• Time and treatment