Enhancing Thinking Skills in Science Context

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Enhancing Thinking Skills in Science Context

• Lesson 4
• Experimental Design

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Activity 1

• A scientist, Dr. Chan, wants to design an
  experiment to investigate the following topic
• The effect of taking a nap (a short sleep
  during the day) on longevity
• 1. Please design an experiment to study this
  research topic using a control group and an
  experimental group.?
• (Use a flow chart / mind map to show your
  experimental design).

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Activity 1

• 2. Please comment on the difficulties Dr Chan
  may face if he carries out his research according
  to your design.
• 3. What are the advantages of this kind of
  experimental design (Randomised Experimental
  Design) in scientific investigation?

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4. Please comment on the difficulties Dr Chan may
face if he carries out his research according to
your design.

• Expensive and time-consuming (for years) to carry
  out the experiment
• ?
• Must involve a large number of subjects for the
  experiment in order to have statistically
  significant results?
• Must keep other variables constant (fair test)
  but in reality it is difficult to control.

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Remarks

• If a scientist wants to study the effect of a
  certain poison on humans, he/she is not allowed
  to choose an experimental and control group at
  random from a large population.

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5. What are the advantages of this kind of
experimental design (Randomised Experimental
Design) in Scientific Investigation?

• Randomised Experimental Design can provide strong
  evidence to support an hypothesis because other
  possible causal factors are controlled in the
  experimental design.

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Activity 2

• Dr. Chan wanted to investigate the link between
  eating fruits and immunity from cold. He selected
  5000 students randomly from 500secondary schools
  in Hong Kong. Then he sent questionnaires to
  these students to collect information about their
  eating habits. He divided them into 2 groups
  those who eat fruits regularly (eating fruits
  every day) and those who seldom eat fruits
  (eating fruits less than three times a week). The
  former became the experimental group and the
  latter became the control group. He found that
  the number of students in the experimental group
  outnumbered the number of students in the control
  group. He then pared down the size of the
  experimental group so that the numbers of
  students in the experimental and control group
  were the same.

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Activity 2

• He then sent another questionnaire to them to
  gather information from them on their frequency
  of getting cold in the following 6 months.

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Task

• 1. Use a flow chart to illustrate the above
  experimental design.
• 2. The experimental design in (1) is called
  Prospective Experimental Design. What are its
  special features?
• 3. What are the advantages of Prospective
  Experimental Design over Randomised Experimental
  Design?
• 4. What are the limitations of this kind of
  experimental design?

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5.The experimental design in (1) is called
Prospective Experimental Design. What are the
special features of the Prospective Experimental
Design?

• The subjects who have been exposed to the
  suspected cause (eating fruits regularly in (1))
  are selected for the experimental group while the
  subjects of the control group who have not been
  exposed to the suspected cause (eating fruits
  less often) are selected for the control group.

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6. What are the advantages of Prospective
Experimental Design over Randomised Experimental
Design?

• Easier and less expensive to carry out the
  study/experiment ?
• May avoid ethical objections ?
• Can pool data from very large group of subjects
  thus increasing the accuracy of the experimental
  result

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7. What are the limitations of this kind of
experimental design?

• The selection process of experimental and control
  group usually focuses on one single causal
  factor, hence it is possible that other factors
  will come into play at the very early stage of
  the selection process (i.e. the selected subjects
  having the suspected cause already affected by
  other factor(s)).

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Activity 3

• Another Design involves the collection of data
  prior to the setting of the objectives and design
  of the research. The data can be abstracted from
  past studies or researches. This kind of design
  is called Retrospective Design.
• Retrospective Design to find the Cause and
  Effect from past data and researches.
• ?
• Key terms ?
• Suspected Cause (independent variable)?
• Suspected Effect (dependent variable)?
• Experimental group a group of subjects chosen
  from the population with the suspected effect (or
  with improvement after treatment)?
• Control group a group of subjects chosen from
  the population without the suspected effect (or
  without improvement after treatment)

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Retrospective Design
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Task

• 1.What would the result of Dr. Xs study be if
  acupuncture treatment can prolong the life span
  of patients with last stage liver cancer?
• 2.What are the pros and cons of Retrospective
  Experimental Design?

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3. What would the result of Dr. Xs be if
acupuncture treatment can prolong the life span
of patients with last stage liver cancer?

• We may look for the percentage difference (life
  span) between the experimental and control group.
  If there is a higher and significant of
  patients who can still live after 1 year in the
  experimental group than that of the control
  group, the study may support the causal link
  between acupuncture and prolonging of life span
  of patients with last stage liver cancer.

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4. What are the pros and cons of Retrospective
Experimental Design?

• (i) The advantages of retrospective experimental
  design are that it is quick and inexpensive. We
  only need to analyse the data of past
  research/study carefully.
• (ii) The disadvantages of retrospective
  experimental design are as follows
• Can only provide weak evidence for a causal link
  because there may be other potential causal
  factors which are difficult to control in this
  kind of experimental design (these potential
  causal factors other than the one to be tested
  for may automatically be built in the
  experimental and control group). ?
• Furthermore, retrospective experimental design
  cannot estimate the level of difference of the
  effect being studied.
• Reference Stephen S. Carey (1998)

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Exercise

• Read the following news and answer the questions

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Inhalation of air with high oxygen concentration
enhances memory

• A Japanese electric appliance company X conducted
  a research and claimed that inhalation of air
  with high oxygen concentration can enhance
  memory. 80 students were divided into 2 groups.
  They were required to take a test on English
  vocabulary. Then the experimental group of
  students inhaled air of high concentration of
  oxygen while the control group breathed ordinary
  air. Both groups of students were allowed to have
  some revision before taking the same vocabulary
  test again. It was found that the experimental
  group could memorise the vocabulary items 15
  more than that of the control group.

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Question

• 1. Name the experimental design used by company
  X.
• 2. Comment on the experimental result and judge
  the reliability of the research findings.