Enhancing Thinking Skills in Science Contex

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					Enhancing Thinking Skills in Science
Context


              Lesson 4
         Experimental Design
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).
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?
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.
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.
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.
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.
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.
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?
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.
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
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)).
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)
Retrospective Design
                       .
Task :

1.What would the result of Dr. X’s 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?
3. What would the result of Dr. X’s 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.
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)
Exercise:

   Read the following news and answer the
    questions:
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.
Question:

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

				
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posted:10/14/2011
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