designing an experiment
THERE IS NO SUCH THING IN THE ENTIRE UNIVERSE AS A CONSTANT VARIABLE. No. Never. Not appropriate. Don’t ever. Don’t even think about it! I mean it.
6 concepts of experimental design independent variable dependent variable constants control group experimental group repeated trials
independent variable the variable that is changed on purpose by the experimenter aka cause, stimulus, reason, manipulated variable, etc. This is the ‘’if” part of a hypothesis.
dependent variable the variable that responds aka effect(s), result(s), responding variable, etc. This is the ‘’then” part of a hypothesis.
constants all factors which are NOT allowed to change during the experiment
control group the group (standard) to which everything is compared
experimental group the group(s) being tested with the independent variable Each test group has only one factor different from the other test groups: the independent variable.
repeated trials important to validate an experiment the number of times the experiment is repeated----atleast3times The more times you repeat the experiment, the more VALID your results are.
chart IVCDV The is used to design an experiment.
iv dv constants fertilizer The variable (factor) that you will change is the independent variable. 0 drops These are the fertilizer amounts varied by the experimenter. 2 drops 4 drops 6 drops
iv dv constants fertilizer plant growth 0 drops The variable (factor) resulting from the independent variable is the dependent variable. 2 drops 4 drops 6 drops
iv dv constants fertilizer amt. of water plant growth type of soil These are the factors that must NOT change during experimentation. They must remain constant. 0 drops amt. of soil 2 drops type ofplant 4 drops type ofplanter 6 drops size of planter type of light location
6 drops fertilizer 4 drops fertilizer 2 drops fertilizer no fertilizer
no fertilizer 6 drops fertilizer 4 drops fertilizer 2 drops fertilizer EXPERIMENTAL GROUP CONTROL What is this called? What are these called?
What are these called? CONSTANTS
What is this called? The plant growth that you observe here can be called . . . theresults (of adding fertilizer) theresponse(to adding fertilizer) dependent variable theeffects(of adding fertilizer) 0 2 4 6
iv constants dv amt. of water fertilizer plant growth type of soil amt. of soil type ofplant Type of soil becomes the IV. type ofplanter size of planter type of light location What do you do if you want to test the type of soil instead of fertilizer? type of soil fertilizer Fertilizer becomes a constant.
In the following two slides, identify the independent variable constants dependent variable.
forming a hypothesis
constants amt. of water type of soil amt. of soil type ofplant type ofplanter size of planter type of light location iv dv fertilizer plant growth + verb + verb Iffertilizer is added to plants, then plant growth will improve.
hypothesis V Chart Dependent Variable Independent Variable + verb + verb If independent variable+ verb, then dependent variable+ verb.