Biology Scientific Method and Vitruvian Man Lab

BYS 120 Lab
Section 03 – Monday 1-3 pm
Section 08 –Tuesday 9:40-11:40 am
Jana Whittle
[email protected]
BYS 120 Lab 2
Scientific Investigation
Image credit:
The Scientific
Image Credit: ArchonMagnus [CC BY-SA 4.0 (], from Wikimedia Commons
• Explanatory statement specific to the research
• Why should the research show a difference
• Must be testable
• Statistically testable or with further experiments
• Must be falsifiable
• Outcomes that should occur based on the hypothesis
• Generally an if…then type of statement
• If hypothesis or explanation then this outcome should be
• Proposed for research that will be tested through statistical
• Proposes that any variance that is measured in the experiment
is due to random chance and not the explanatory hypothesis
Independent Variables
Dependent Variable
Control Variable
Control Treatment
A variable that is changed to
observe a response
A variable affected by the
A factor that is kept constant
across all treatments
A group that is not manipulated
during the experiment
A treatment applied to the
subject of the experiment
Measured or counted in the
observational response
Example: The temperature is
kept constant for all mice
Usually plotted on the x-axis
Usually plotted on the y-axis
Serves as comparison for the
observations seen in the
experimental subjects
Example: Varying the amount of
sugar in diet of mice
Example: The weight gain/loss of
each mouse
Example: A group of mice that
were fed a standard mouse diet
Variable Types
Image Credit:
of Central
Average of
measured values
Middle of the
measured values
Add all values and
divide by number of
Values must be
ordered from
lowest to highest
Use when data is
evenly spread out
Determine the
middle value
If even number of
values use average
of 2 middle values
Useful when data
has outliers
The most
occurring value
Useful when data is
clustered out one or
two values
of Dispersion
Standard Deviation
Standard Error
Span of the values
Quantifies variability of
the values
Quantifies dispersion
around the mean
Widely scattered values
indicate more variability in
the data
Indicates confidence of the
Spread between largest
and smallest values
Find maximum value and
subtract the minimum
Expressed in terms of the
central measurement
Eg: Variability around the
Calculated using mean and
standard deviation
Error generally decreases
as the number of samples
Inferential Statistics
 Inferential Statistics determine if the hypothesis is supported
 Measure whether the observed values are an effect of the experiment or can be
explained through random chance
 p-values are used to make this decision
 Range from 0 to 1
 0 observation impossible due to chance
 1 observation entirely due to chance
 < 0.05 is threshold for determining the observations were not due to chance alone – reject
the null hypothesis
Lab 2
 Lab 2: Test a hypothesis of the human body
 Vitruvius proposed a ¼ rule of human proportions
Middle of chest to top of leg
Bottom of knee to bottom of foot
Top of head to middle of chest
Top of leg to bottom of knee
 He also proposed the arm span was equal to height
Lab 2: Test Vitruvius proposal that human arm
span and height are identical
Lab 2:
Lab Activity
 Write a explanatory hypothesis and prediction.
 Write a null hypothesis and prediction
 Sketch an image of how arm span and height will be
 Measure arm span – to nearest 0.1 cm
 Measure from tip of middle finger to tip of other middle
 Stretch arms wide apart and parallel to the floor
 Measure height - to nearest 0.1 cm
 Measure from top of head to the floor
 Stand barefoot, upright and against the wall
 Record the values for entire class in the table
Lab 2: Assignment (10 points)
Due in Canvas in 24 hours
Lab 2:
Lab Assignment
Upload a Word file to Canvas that includes:
 Explanatory hypothesis and prediction
 Null hypothesis and prediction
 Follow lab manual instructions to:
 Calculate descriptive statistics and report them in a table –
round to one decimal place and include units
 Generate a figure for your data – label axis with units and
include a caption
 Draw a conclusion for your hypothesis by using a t-test and
report the p-value
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