Data in Biology

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Data in Biology
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Lousy data

• Biological data, perhaps more than most other
  scientific data, has the following
  characteristics

• It is complex
• It is incomplete
• It is error prone
• It contains the answers to questions of
  biological function and indeed, dysfunction
• It is in high demand by a community with
  difficult questions

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What is data?

• Any quantifiable information (e.g., wing length,
  number of bristles, gene expression, frequency of
  albinos, etc.).
• A single datum is not amenable to statistical
  analysis
• Hence data needs to be obtained from a number of
  individuals or groups, not merely from a single
  individual, or at multiple times from the same
  individual.

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Examples of biological data

• Ecological data
• Behavioral data
• Molecular data (DNA, protein)
• Physiological data
• Population genetic data
• Quantitative genetic data
• Etc.

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Why collect data?

• To describe a behavior, a phenomenon, a
  structure, etc.
• To test a hypothesis

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Data and hypotheses

• Data are very important to the advancement of
  knowledge, but they are only half of the science.
  
• Biological hypotheses (or research questions) and
  ideas are the other half.

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Data and hypothesescontd.

• Think of it in this way
• Hypotheses ( research questions) without data
  are not very useful, and
• Data collected without hypotheses (or research
  questions or haphazardly and without purpose)
  are wasted.

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Lets explore the nature of data

• When you collect biological data, what is the
  perhaps the most obvious and odd thing about it?

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Variation
Sometimes it is obvious
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Variation
Sometimes it is not
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Why is there variation?
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Variables under direct human control

• If a bank offers an interest of 5, then the
  relationship between the interest accumulated and
  the period of investment is linear
• (y 5x)
• E.g., for 1000.00 invested

Year Int. accum. ( of cap.) 1 5 2 10 3 15 4 2
0 5 25
An important feature of such data is that there
is only one value of the dependant variable for a
given value of the explanatory variable.
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Variables not under direct human control

• Growth rate (of fish, etc.)
• Response of living organisms to treatment (drugs,
  hormones, feed, etc.)
• Expression levels of a gene in different tissues
• The DNA sequence of a given gene in different
  individuals
• Daily rainfall in a given city
• The number of mycorrhizal spores at different
  depths of a plant root
• Etc.

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The changing face of biology
Fig 1.1 from Biometry by Sokal and Rohlf (3rd
editiion), 1995
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Why??

• Biology has gone beyond the descriptive phase.
• Need answers to how and why and not merely
  what.
• Processes involved in answering these questions
  are not deterministic in their effects.
• Stochastic or random effects present that
  cannot be individually identified.

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Boring vs Interesting Data

• If the response can be determined exactly (no
  variation), this is deterministic not in the
  realm of statistics
• If response varies randomly, then such data is
  amenable to statistical analysis

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The free-kick, friends and growth
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What to do with data?

• OK, let us assume you have collected the required
  data (which is a whole chapter in itself).
• The data refers to the standard length of 1000
  tilapia (Oreochromis niloticus) fry
• What do you do with it?

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Frequency Distributions
Figure 2.1 from Biometry by Sokal and Rohlf, 3rd
edition, 1995
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Distribution of a variable

• Shape of frequency distribution
• Most shapes can be approximated mathematicallly
• Of considerable biological interest

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Histogram
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Bar diagrams
This bar diagram shows the photosynthesis of
three aquatic plants during experiments when they
were exposed to UV light. The first group of bars
shows that all three plants were healthy at the
start of the experiment. The second group shows
that after 5 hours of UV light one plant is still
healthy but the other two are under stress. The
third group shows photosynthesis after the plants
were left for 20 hours with the UV lights turned
off one plant did not completely recover.
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Stem and Leaf Plots

• Total length of 17 aphids (mm x 10)
• 8.8, 8.4, 9.0, 9.2, 10.1, 6.3,
• 7.8, 10.6, 10.9, 6.5, 7.7, 7.2,
• 8.6, 9.6, 8.5, 9.7, 8.7