The DEPENDENT VARIABLE (see “words you need” page for a definition) must be quantitative. That means it can be measured in numbers (as opposed to qualitative variables that are described with adjectives)

**You could measure…**

• size or a change in size: weight, height, length, volume, area, perimeter, diameter

• speed (= distance / time)

• concentration (= # / volume)

• density (= mass/volume)

• frequency (how often something happens)

• angles and/or direction

• percent coverage, percent change (loss or increase)

• and many other things like temperature, humidity, light, sound, pH, wind speed, direction, water quality, tidal height, heart rate, blood pressure, reaction time

The INDEPENDENT VARIABLE can be either quantitative or qualitative.

Examples of **qualitative variables **would include:

• color: red, blue, green, yellow, orange

• male/female

• small, medium, large

• slow, medium, fast

• high, low

• old, young

• labels for groupings: A, B, C, D, E

• any type of category

Loretta depaoliMy son is going to do a science fair project using 3 different types of popcorn. He is going to find out which one leaves the least amount of un popped kernels if using the directions. Then he is going to soak the kernels in water for 24 hours and then pop according to directions. He will try each brand 3 times. Question: what is the dependent and independent variables? Should he graph the average of the 3 trials or should he graph the 3 trials for each brand

Dr. Maille LyonsIt looks like he will have two independent variables 1 = (unsoaked vs. soaked) and 2 = brand of popcorn; and one dependent variable (number, or even better, percentage of unpopped kernels).

There will be a few different ways to make the bar graphs depending on what he wants to highlight. For example, he could construct a bar graph showing the percentage of unpopped kernels for un-soaked (i.e. the control) vs soaked for each brand (3 graphs each with a control bar plus three trial bars for run 1, 2, and 3). He could also make a graph showing the average percentage of un-popped kernels for each brand (one graph with three bars, one bar for each brand based on an average and a standard deviation) or put all three bars for each brand together to show the percentage of unpopped kernels for each brand when soaked (1 graph with 3 sets of 3 bars). He could also calculate the percent enhancement or worsening based on soaking (calculate the difference between the control = unsoaked and the soaked to show soaking improves or does not improve the percentage popped/unpopped).

Do not group by trial because that isn’t logical – so do not make a graph with the results of each first popping, second popping and third popping with each brand next to each other. Rather group results (bars) by brand for the three sets of three bars because that will also show how variable each brand is.

Hope that helps!

StarI am teaching a Science Class at a home school tutorial. Our Science Fair is Tuesday. I have a student that just emailed me (Thurs. night) saying he was growing bacteria (he did use an approved lab) but that no samples grew. Obviously at this point, he does not have time to repeat the experiment. He wants to know how he can include a graph. How would you instruct a student?

Dr. Maille LyonsTechnically, if he has no data, he can not make a graph.

You could have him make a “data table” with two columns – including “Expected Outcome” (have him describe what he thought would happen) and “Actual Outcome” (stating nothing grew) and then maybe a explanation somewhere as to what he thinks went wrong and why nothing grew.

StarThanks bunches!!!

Alexa WirthHello I am trying to help my grand daughter with a project on “what makes an ice cube melt faster sugar or salt? i don’t understand what the teacher means with ” Data/graphs

Dr. Maille LyonsData refers to the measurements you will make; Graphs are one way to present those measurements.

You will be able to make a bar graph with “Treatment” on the x-axis (one bar for sugar, one bar for salt); and “Time to melt” on the y-axis.

Ayleen WolfeHi there! My son is doing a science project on tooth decay. He plans on putting hard boiled eggs in different liquids like vinegar, coca cola, hi c, and water….How could we measure the results and put them in a graph? Maybe weighing each egg to see if there is a change? Meaning, tooth decay= decrease in weight of tooth therefore decrease in weight of egg too after exposure to coke and hi c? or would measuring circumference of each egg be better? I am not sure how to help him with measurement. Thanks

Dr. Maille LyonsYou’d have to try it to see if it works – the issue will be if you can actually measure a difference. That will be determined by how good your scale is (for weight) or how precisely you can measure circumference (e.g. calipers would be better than a tape measure), but if the difference is on a very small scale, for example micrograms, or milligrams, or micrometers – then your tools are probably not good enough to measure any difference that occurs.

That is typically the problem with this type of project – the dependent variable is not quantitative – it’s qualitative – you may see a difference and even feel a difference, but you can’t put either of those on a graph unless you have a way to measure them quantitatively – i.e. a number

Hagman AcademyMy daughter’s project is “What area of an average American home will grow the most bacteria”? How would she display a graph? either line, bar or pie?

Dr. Maille LyonsMost likely it will be a bar graph. Put the area of the house on the x-axis (horizontal) and whatever she measured to determine the amount of bacteria on the y-axis (vertical)