BENCHMARK 2: Identifying HYPOTHESIS & VARIABLES
(due Monday 3.3)
Objective: To be able to identify the independent, dependent, & controlled variables for a research study or
experiment.
BACKGORUND INFORMATION:Define
the Variables. There are three categories of variables in
every experiment: dependent, independent, and controlled.
Dependent -- is what will be measured; it's what the investigator thinks will be affected during the
experiment.
For example, the investigator may want to study coffee bean growth. Possible dependent variables
include: number of beans, weight of the plant, leaf surface area, time to maturation, height of stem.
Independent -- is what is varied during the experiment; it is what the investigator thinks will affect
the dependent variable.
In our coffee bean example, possible independent variables include: amount of fertilizer, type of
fertilizer, temperature, amount of H2O, day length, all of these may affect the number of beans,
weight of the plant, leaf area, etc.
Key : Since you need to know which factor is affecting the dependent variable(s), there may be
only one independent variable. The investigator must choose the one that he/she thinks is most
important. But the scientist can measure as many dependent variables as he/she thinks are
important indicators of coffee bean growth.
Controlled -- the variables held constant. Since the investigator wants to study the effect of one
particular independent variable, the possibility that other factors are affecting the outcome must be
eliminated.
For example, the above scientist must ascertain that no differences in the type of fertilizer used
exists, or amount of H2O, variations of temperature, or day length exist.
Hypothesis - A hypothesis is an educated guess about how things work.
•
Most of the time a hypothesis is written like this: "If _____[I do this] _____, then
_____[this]_____ will happen." (Fill in the blanks with the appropriate information from your
own experiment.)
•
Your hypothesis should be something that you can actually test, what's called
a testable hypothesis. In other words, you need to be able to measure both "what you do" and
"what will happen."
HYPOTHESES and VARIABLES PRACTICE
Write a hypothesis for each of the following problems.
1. What effect does high temperature have on radish germination?
2. What effect does studying with music have on student test scores?
3. What effect does food color have on the amount of food fish eat?
4. What effect does light have on plant growth?
5. What effect does smiling have on the teacher giving no homework?
For the following problems, identify the independent variable (IV), dependent variable (DV),
controlled variables (SV), and control group (CG) – if applicable
1. The number of flowers on different breeds of bushes in a greenhouse is recorded every week for 2 months.
IV =
DV =
CV =
2. You give four sunflowers different watering with either pure water or different concentrations of salt
solutions. After a 2 week period, the height is measured.
IV =
DV =
CG =
3. Three redwood trees are kept at different humidity levels inside a greenhouse for 12 weeks. One tree is left
outside in normal conditions. Height of the tree is measured once a week.
IV =
DV =
CV =
CG =
4. Pea plant clones are given different amounts of water for a 3 week period. The first plant receives 400
milliliters of water, the second gets 200 mL, and the third receives 100 mL. The fourth does not receive any
extra water; the plant only receives natural ways of receiving water. The height is recorded daily.
IV =
DV =
CV =
CG =