Important Parts of Scientific Experiments Variables and Control

Important Parts of Scientific Experiments Variables and Control Group

Variables �In any scientific experiment there are 3 kinds of variables. �Each kind serves a specific purpose in good experiment design. (Step 4 of the Scientific Method) �You should be able to identify each type and understand their function.

Variables �Independent Variable Also called the manipulated variable. The variable that is changed throughout the experiment in order to see what the result of changing it is.

Variables �Dependent Variable Also called the responding variable. The variable that changes in response to the independent variable. This is the change (or result) the scientist is studying.

Variables �Controlled Variables Everything else in the experiment must be controlled and kept as exactly the same as possible. This ensures the changes noted in the dependent variable can only be caused by the manipulation of the independent variable.

Variables �The variables in the experiment are directly determined by the hypothesis. �If you have constructed a good hypothesis (Step 3 in the Scientific Method) then your variables will be easy to determine.

Variables Practice �Hypothesis: Using different brands of fertilizer will result in different plant growth rates. Independent Variable (IV): ▪ What am I changing? ▪ Fertilizer brand

Variables Practice �Hypothesis: Using different brands of fertilizer will result in different plant growth rates. Dependent Variable (DV): ▪ What change am I measuring? ▪ Plant growth

Variables Practice �Hypothesis: Using different brands of fertilizer will result in different plant growth rates. Controlled Variables: ▪ How am I sure the difference in plant growth is caused only by the different fertilizer? ▪ BY MAKING EVERYTHING ELSE THE SAME ▪ Water, sunlight, pot size, plant type, measurement technique, type of soil, plant size at start, ambient temperature…and so on. . .

Variables Practice �Hypothesis: Increasing salt concentration in water will decrease boiling point. �Independent Variable: �Dependent Variable: �Control Variables: salt concentration boiling point pot size, amount of salt water, altitude, pot type, pot material, thermometer type

Variables Practice �Hypothesis: Drinking an energy drink before bed will result in less sleep. �Independent Variable: �Dependent Variable: �Control Variables: drinking energy drink amount of sleep bedtime, place of sleep, brand of drink, type of drink, amount of drink, how long before bedtime it is consumed

Variables Practice �Hypothesis: Certain essential oils will act as an insect repellent. �Independent Variable: �Dependent Variable: �Control Variables: essential oil type insect repellent ability concentration, amount applied, application method, exposure time

Types of Variables

Control �Having a control is a very important part of a valid scientific experiment. It is also sometimes known as a “control group. ” �A control, or control group, is a group that the independent variable is not given to in order to have a baseline to compare the results of the test subjects.

Control Identification Practice �Experiment: A new drug is developed to help lower cholesterol without changing diet or exercise. Four groups are studied; no person knows which group they are in. Group 1 is given a placebo (sugar pill); group 2 is given 50 mg per day; group 3 is given 100 mg per day; group 4 is given 200 mg per day. Which is the control? Group 1

Control Identification Practice �Experiment: The toxicity of a new shampoo needs to be tested. Skin irritation is measured on rabbits after the following treatments: Washed with water for 1, 2, 3, and 4 minutes Washed with shampoo for 1, 2, 3, and 4 minutes Which is the control? The rabbits washed with water

Control Identification Practice �Experiment: Plant growth is measured and compared between plants given the following liquids: apple juice, orange juice, soda water, Coke, Pepsi, sugar water, distilled water, whole milk, and brewed coffee. Which is the control? distilled water