Models in Science
A model is a labeled diagram, web, or mind map that represents real-world
phenomena. Models should be accurate; anything you’re not sure of should
have a question mark beside it.
In the model to the gum lab, your model will show all the factors we can
think of that affect gum stretchiness and how those factors are connected.
You can draw your model in the form of a web or a diagram.
There will be gaps in our knowledge - a model makes these gaps apparent,
leading to questions that can be researched to gather more information.
Once a variable to be researched is identified, the model can be used to find
important constants for your experiment.
-----------------------------------------------------------------------------------------------------Cognitive Apprenticeship
What is the importance of a knowledge model when doing science research?
• Provides a representation of a real world phenomena
• Explains why things happen – explanatory
• Can be tested - testable
• Makes gaps in knowledge explicit - generative
• Gaps in knowledge filled in through require evidence (through
investigation) to expand - conjectural, revisable
• clarify questions
• identify important variables that can be measured
Experimental Design - should always be in this order and this format
Research Question: This should be based on a scientific concept and should
come from your model.
Null hypothesis: The independent variable will have no effect on the
dependent variable.
Alternative hypothesis 1: One factor will have a specific effect on the DV.
(Gum chewed for 6 minutes will stretch farther than gum chewed for 3
minutes.) This should be based on scientific knowledge; there should be a
scientific reason for choosing this as the main alternative hypothesis.
Alternative hypothesis 2: The same factor will have the opposite effect on
the DV. (Gum chewed for 3 minutes will stretch farther than gum chewed for
6 minutes.)
Independent variable: (be specific)
Experimental groups: (be specific)
Control group: (select one of the experimental groups)
Dependent Variable: (be specific) (what is to be measured, how it will be
measured, in what units)
Constants: (important ones - refer to your model)
Cognitive Apprenticeship
1. Experimental designs are based on scientific knowledge.
2. Experimental designs should come from the model.
3. Scientists test ideas, not things.
Data collection: Data collection is not a mindless activity!
Raw data table: Group data should be recorded in a raw data table in your
lab notebook. Experimental groups across the top; units in row labels only.
Distance Gum Stretched (cm)
Time gum chewed
(minutes)
2
4
6
Trial 1
Trial 2
Trial 3
This is “raw” data and will not be included in the lab report.
Enter group data into class Excel spreadsheet.
Descriptive statistics table:
1. Include central tendencies (mean and/or median) and measure of
variation (standard deviation).
2. Experimental groups go across the top.
3. This table should be in your lab notebook and in the lab report.
4. Decide what kind of IV you have (quantitative or categorical/qualitative).
5. Decide what kind of DV you have (quantitative or
categorical/qualitative).
Cognitive Apprenticeship
1. Data collection is not a mindless activity!
2. As scientists collect data, they notice if:
a. any of the data looks unexpected
b. the equipment isn't (a reading of 12 indicates an error with the
sensor)
c. there are problems with the procedures that will affect the data
Descriptive statistics of class data:
1. Central Tendency: Mean and Median - describe the middle value of all of
the data
Central Tendencies:
o mean: arithmetic average - used for normal distribution
o median: middle number - used when there are outliers
o We often report both
2. Variation: Standard Deviation (SD) - describes how much the data varies
around the mean.
o
o
o
The SD is a measure that is used to show the amount of variation of a
set of data values.
A standard deviation close to 0 indicates that the data points tend to
be very close to the mean.
A high standard deviation indicates that the data points are spread
out over a wider range of values.
3. The descriptive stats table should have:
o
o
o
o
title that is informative (not “gum lab”) and is in title case
experimental groups across the top
row for central tendencies (with units in the row label, not with the
numbers)
row for standard deviation (with units in the row label, not with the
numbers - same units as data)
Cognitive Apprenticeship
A descriptive stats table communicates the findings to your reader in a
simple format.
Graphing class data - which type of graph to use to communicate the
statistics
1. All graphs will include:
o informative title in title case
o labels for x and y axes (sentence case) with units  IV goes on the x-axis (“I X-pect to get an A”)
o correct scaling of axes
 use at least half the graph space
 correct number lines on both axes
 remember to calculate highest value + SD and lowest value - SD
before making y-axis scale
2. Quantitative independent variable - Is there a relationship between
variable x and variable y and both data are
numeric?
o Example: Does cell size influence rate of
diffusion?
o use scatterplot
 include all data, or
 means (dot only) and SD error bars
3. Quantitative independent variable - Does the dependent variable change
over time?
o use line graph
4. Qualitative (categorical) independent variable o Example: How does cell type influence the
rate of diffusion?
o central tendency and variation must be
shown on graph
o multiple options:
 multiple histograms - shows all of the data effectively
 box plot - shows median, variation, and skewness
 bar graph - most MISUSED graph - MUST include SD error bars
Results
o
o
o
paragraph format
past tense and passive voice,
presents the findings in words, does not explain the findings
Include (in order):
o
o
o
Make a claim: Write a statement that answers the research question
(Does the IV affect the DV?).
Summarize trends in the data. (Refer to central tendency and variation
(standard deviation).
Restate the null hypothesis (use quotes). Was the null hypothesis
accepted or rejected?
Proof read:
o
o
o
o
o
o
no personal pronouns - use passive voice
no contractions
be specific
use scientific vocabulary
capitalize proper nouns
do not capitalize common nouns - if you’re not sure, look it up
Cognitive Apprenticeship
Discussion
In paragraph format, using past tense and passive voice, discuss the
following:
1. Make a claim
o Restate the claim to focus the reader on the answer to the research
question.
2. Explain the scientific concepts behind the claim
o State the scientific concepts that are generally accepted as true
(warrants). Warrants are found in your background information.
o Give more details that support the warrants (backing).
o Give your evidence (data analysis) that supports the claim
3. Give alternative explanations that can also explain the data obtained
(counter arguments or qualifications)
Proof read:
o
o
o
o
o
o
no personal pronouns - use passive voice
no contractions
be specific
use scientific vocabulary
capitalize proper nouns
do not capitalize common nouns - if you’re not sure, look it up
Cognitive Apprenticeship
The discussion should convince the reader (me) that you know how the
science works
o how the IV affected the DV
o why the IV affected the DV
_______________________________________________________________
Conclusion
In paragraph format, using past tense and passive voice, summarize the
knowledge gained from this experiment in 1-3 sentences.