Happy Friday Scientists! DQ: Identify the IV, DV and constants in the following scenario: A study was done to find if fuel types affect the engine’s performance in a car. Today: Review Density Lab What are the different types of data and which type of graph should we use for each? (study guide) Data and Graph Types Practice Review IV/DV/Constants HW: Return work and discuss grades L4

Variables and Constants Variable – Any factor that can change in a scientific investigation or experiment

Types of Variables Independent Dependent What the scientist chooses or changes Known before starting the experiment. The factor that is intentionally changed by the investigator in an experiment There can be only one independent variable in an experiment The factor that you measure or observe as data The factor that will change as a result of the independent variable This variable depends on the independent variable. There can be one or more dependent variables in an experiment

Constants Sometimes called controlled variables The factors or conditions that are kept the same (unchanged) in an experiment There are many controlled variables in an experiment.

Graphing Study Guide Are you ready to go? Complete the handout!

There are 4 major types of graphs we’ll use this year. I can remember that

Types of Data Discrete data = consist of categories (days of the week, kind of animal, color) Continuous data = consist of measurements involving a scale with equal measurements; a range of values (temperature, length of time in hours, height in centimeters)

Four major types of graphing Pie chart/graph = consist of categories (display percentages) Bar graph = used to represent discrete data; the IV is typically qualitative and DV is typically quantitative

Four major types of graphing 3. Line graph = used to represent continuous data, usually tracking changes over time; the IV and DV are both quantitative and the line connecting the points has meaning 4. Scatter plot = similar to a line graph, but the data points are NOT connected because a connecting line would have no meaning; a line of best fit might be constructed to show a trend in the data; IV and DV are typically both quantitative

Scatter plot This is a line of best fit – it is a straight line that comes as close to possible as all the data points The data points should NOT be directly connected because the IV is discrete

Bar Graph This is what we mean by discrete data – it’s a category and there’s no “middle value” between each category

Line Graph Each value here has meaning (I could determine Jill’s elevation at 3.2 hours) so I connect my data points with a line

Pie chart Here I have data organized in a percentage out of 100 – this is good way to represent it

A few final thoughts Scientists must represent their data graphically in a fair way that tells the most accurate story It is possible to change the scale of a graph to make it look like the data tells a much different story than the numbers actually show Additional labels might also be used to make the reader infer certain things from the same set of data

For example… At most, how different is the average rainfall from this year’s rainfall? This graph has been manipulated to make it look like there is a much bigger difference in rainfall than 0.4 cm Bad scientist!

A more accurate graph Good scientist!

Another Example What conclusions can you draw from this graph? U.S. Jobs by Quarter Number of jobs (thousands) Quarter, Year Image source: http://www.politicalmathblog.com/?p=401

Here’s the same graph with a few extra labels… The data is the same but it could be used to create different inferences Image source: http://www.politicalmathblog.com/?p=401

Examples What is the scientist changing? (independent variable) The temperature of the ball What is the scientist measuring? (dependent variable) Bounce height of the ball when dropped What should be kept the same or constant for a fair test? (constants) Same ball Dropped from same height Onto same surface. Etc. Question: Does changing the temperature of a ball affect the height the ball will bounce?

Question: Does changing the color of light change the growth rate of plants? Independent? Color of light Dependent? Growth rate of plants Constants? Age of plant Type of plant Amount of light Amount of water When measured Type of container Etc.