Unit 1 – Lecture 2

Harold owns two hamsters – they live in separate cages, but they’re exactly the same in every other way [age, weight, cage design, etc]. Suddenly, the hamsters start gaining weight – but he has always fed them the same food [Food A] and has been feeding them the same amount. He decides to go to the store to check out new food options. A clerk at the store tells him that he’s heard of a different food, Food B, that causes less weight gain than the other foods. Harold thinks that the clerk might just be being sneaky to make a sale, so he talks to other people in the store – but they all say the same thing. He decides to purchase a small bag of Food B and test it on hamster #1 before he feeds it to his favorite hamster, #2 to see if food B will cause less weight gain. Based on talking to so many people, he thinks it probably will.

The Scientific Methoda tool used to solve problemsused by EVERYONE – not just scientists

Steps in the Scientific Method

• develop Problem ……Statement

• collect Background …… Info• form Hypothesis

• perform Experiment• collect Data

• analyze Data• form

Conclusion

• Observe

Defining VariablesIndependent Variable [IV]

• changes the other variable [DV]• “I control the IV”

• it is not changed by the other variable [it is INDEPENDENT of the DV]

Dependent Variable [DV]• is changed by the other variable [IV]

[ it is DEPENDENT on the IV]

Defining Variables - ExampleGiven the purpose statement below, what 2

things will you measure in your experiment?Purpose: to determine whether food B will

cause less weight gain than food A [normal food] in a hamster when fed over a period of 2 weeks.

Variable 1: TYPE of food --it is important to note that you are NOT

measuring the impact of the food’s color, size, shape, or other characteristic.

Variable 2: amount of weight gain

Defining Variables – cont’dThe DV depends on the IV. I change the IV.Which of these sentences makes sense?

The type of food fed to the hamster depends on the amount of weight the hamster gains.

ORThe amount of weight the hamster gains

depends on the type of food fed to the hamster.

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Defining Variables – cont’d“The amount of weight the hamster gains

depends on the type of food fed to the hamster.”

IV = type of food [“I control the IV” !!!!!]DV = weight gain of hamster

Test GroupsTwo different groups in an experiment:Control Group - group that does not receive the

treatment or changefunctions as a standard by which you can

measure the results of your experimentwe know that what we are testing is NOT

affecting this groupHamster #2 being fed Food A [the “normal”

food].

Test Groups – cont’dTwo different groups in an experiment:Experimental Group – group in the

experiment which receives the change/treatmentwhat we are testing IS affecting this groupHamster #1 being fed Food B [the “new”

food].

ConstantsConstant – something you want to remain the

same throughout an experiment.Purpose: to figure out whether food B will

cause less weight gain than food A [normal food] in a hamster when fed over a period of 2 weeks.

DiscussWhat things need to remain the same in order

for you to be sure that ONLY the difference in type of food is causing the change in weight?

Come up with a list of 5 or more things.

What’s the Point? No Constants, No Confidence

HypothesesForming a Hypothesis

If, Then formatstatement, NOT a questioncontains IV and DVpredicts specific outcome of the

experimentwhat type of change are you making?what type of change are do you predict you’ll

see?

abbreviation [used frequently] for change = Δ

Hypotheses – cont’dTypes of Hypotheses

Hypothesis – predicts change in the results between the control & experimental groupsIf [change] in IV, then [change] in DV

Null Hypothesis - predicts no change in the results between the groupsIf change in IV, then NO CHANGE in DV.

Hypotheses – cont’d the POINT of the NULL

hypothesis is to be rejected / disproven.

it states that there’s no relationshipbetween your variables.

DiscussCome up with a null hypothesis for each hypothesis

below. [states no change or no relationship between your variables].

Patients taking drug A for their headache will recover faster than patients taking a placebo.

NULL: Patients taking drug A for their headache will recover in the same time as patients taking a placebo.[no change in recovery time]

Tomato plants exhibit a higher rate of growth when planted in compost rather than in soil.

NULL: Tomato plants show no difference in growth rates when planted in compost rather than soil.[no change in the growth rate]

Performing the ExperimentAs part of performing the experiment, the

following must be completed:materials LIST for the experiment

contains ALL equipment used in ALL groups

contains how many of each item are usedLIST of steps in your procedure

be specificimportant – need to have repeatable

results

Collecting DataCollecting data takes place during the

experimenttypically in a data tabletitle of table contains IV and DVIV on left, DV on rightfinalized table has data in numeric order

according to trial number OR in ascending order if there aren’t specific trials.

Analyzing DataAnalyzing data takes place after the experiment.

typically in graph form [IV on X-axis, DV on Y-axis]

Comparing Qualitative & Quantitative Datatypes used: bar graph, pie chart

qualitative data – data involving characteristics [qualities – color, type, etc.]

quantitative data – numerical data [quantities]

Analyzing Data – cont’dComparing two types of Quantitative Data

scatter plot – line graph w/o the lineline of best fit – drawn through the

average of the plotted points

line graph – connects the dots between sequential points

Question:What kind of graph should we use for our

hamster experiment graph?

variables: type of food, amount of weight gain

ConclusionsConclusions contain:

a restatement of the purposea description of data analysisa restatement of the hypothes(is/es)a statement of accepting or rejection of

hypothesis& other stuff you’ll see on a rubric specific

to each lab

HomeworkComplete pg 6 of your Unit Packet

Simpsons & the Scientific Method w/s