Experimental Design

Experimental Investigation

The organized procedure used to study an aspect of the natural world under controlled conditions

Experimental Design

Testable Question

Research

Hypothesis

Materials/Procedure

Data Collection

Data Analysis

Conclusion

Testable Questions

Asks the question to be answered in an experiment

Includes both the independent variable and the dependent variable

How does ____(Independent Variable)____ affect ___(Dependent Variable)____?

What is the effect of ___(Independent Variable)___ on ___(Dependent Variable)____?

Practice Writing a Testable Question

Using the following information, write a testable question:

Independent variable: hours of studying

Dependent variable: grade earned on a test

Hypothesis

A prediction based on prior knowledge (research) about the expected relationship between the variables in an experiment

Includes both the independent variable and the dependent variable and a reason

Is either supported or rejected by the experiment

Frequently written as an “if…then” statementExample “If the amount of sunlight received by a plant is increased, then the plant will grow taller because plants require sunlight for photosynthesis”

Practice Writing a Hypothesis

Write a hypothesis for the following question:

What is the effect of exercise on a person’s heart rate?

Research

Before beginning an experiment, quality research must be conducted to gather background knowledge

Reliable sources (peer-reviewed journals, textbooks, etc.) *Not wikipedia or blogs*

Also included in the background knowledge are previous observations

Parts of an Experiment

Independent Variable

Dependent Variable

Controlled Variable

Independent Variables

Also called manipulated variables

Changed (manipulated) directly by the scientist

Graphed on the X-axis (horizontal)

Dependent Variables

Also called responding variables

Change as a result of the manipulation of independent variables

Graphed on the Y-axis (vertical)

Controlled Variables

Also called constants

Do not change during an experiment

Must stay the same in order to ensure a fair test

Control Group

A standard or “baseline” group to which the experiment is compared

The independent variable is not changed in the control group

For example, if the scientist is testing how the addition different fertilizers affect a plant’s growth, the control group would be a plant that does not receive any fertilizer

Materials List

List specifically all materials used in an experiment

Include quantities and units

For example, “beakers” is not specific. Instead, write “5 100 mL beakers”

Procedure

A step-by-step guide to conducting an experiment

Procedures must be specific and detailedInclude all tools and materials being used in that step

Procedures should be detailed enough that the experiment can be repeated by another scientist

Organizing Data

Quanitative (numerical) data is organized into tables or charts in rows and columns

Specific independent variables are listed

The number of trials are listed

Blanks are left to fill in measured data (dependent variable)

Title Describing the Data(ex: Independent Variable vs.

Dependent Variable)Trial Independent

Variable 1Independent Variable 2

Independent Variable 3

1

2

3

4

Average

Analyzing Data

Reduce the data: do something to make the amount of data smaller

Central tendencies:Mean

Median

Mode

Range

Frequency

Bar Graphs

Uses rectangular bars of different colors/patterns to display data

Used for comparisons

Line Graphs

Uses points connected by a line to show how values change

Useful for showing trends

Scatter Plots

Uses unconnected points to display data

Useful for showing correlations between variables

Note: correlation does not imply causation!

A correlation between variables does not necessarily mean that one immediately caused the other to change

Positive Correlation

An increase in the variable on the X-axis is associated with an increase in the variable on the Y-axis

Negative Correlation

An increase in the variable on the X-axis is associated with an decrease in the variable on the Y-axis

No Correlation

Random data points – there is no association between the variables

DRY MIX

Dependent

Responding

Y-Axis

Manipulated

Independent

X-axis

Let’s Practice

Title

Independent Variable

Dependent Variable

X

Y

*Don’t Forget*

Every time you make a graph, include:

Descriptive title (ex: Independent Variable vs. Dependent Variable)

Labeled X and Y axes… Include UNITS

Legend (if necessary)

Scale/Interval of axes (3, 6, 9, etc)

Let’s PracticeTime (minutes)

Cart 1 Distance (m)

Cart 2 Distance (m)

Cart 3 Distance (m)

1 1 2 3

2 2 4 6

3 3 6 9

4 4 8 12

A student built three different wooden carts to test the effect of different power sources (battery, wind, and solar) on the speed of her carts. Her data is represented in the table above.

Conclusion

Answers the original question

Restate the hypothesis

Accept or reject the hypothesis and support using evidence from the investigation

Describe relationships in the data

Explain any inferences made using the data

Discuss any problems or sources of error that occurred during the investigation

Discuss any extensions or elaborations on the topic

Publish!

New knowledge is useful when it is shared

Journals, publications, presentations