Formulating a Hypothesis
It’s Science!
Hypothesis
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A Hypothesis is an educated guess that is testable
A Hypothesis is an assumption about a population
parameter
If, Then, Because (Hypothesis and Prediction)
If, The, Because, How (Hypothesis, Prediction and
Methods)
www.sciencebuddies.org
Definition, examples & checklist
The Null and Alternative Hypothesis
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The Null hypothesis, denoted by H0 ,
represents the status quo and involves
stating the belief that the mean of the
population is <, =, or > a specific value.
The alternative hypothesis, denoted by H1 ,
represents the opposite of the null
hypothesis and holds true if the null
hypothesis is found to be false. (<, not =, or >
a specific value)
Example
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Let’s say that my hypothesis is that it will take an
average of 6 days to capture a loose snake in a
house. (population mean is = to 6 days)
Suppose after I gathered a sample of people who
had snakes loose in their home and averaged the
data, I found it took 6.1 days. The hypothesis test
will then tell me whether or not 6.1 days is
significantly different from 6 days or if the difference
is merely due to chance.
Example Continued
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H0 : µ = 6.0; µ > 6.0; µ < 6.0
H0 : µ is not = 6.0; µ > 6.0; µ < 6.0
Show graph of Two-tail hypothesis test (p. 217)
The curve in the figure represents the sampling
distribution of the mean for the number of days to catch a
snake. The mean of the population, assumed 6.0 days
according to the null hypothesis, is the mean of the
sampling distribution.
Procedure
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Collect a sample size, n, and calculate the test statistic, which
is usually the sample mean
Plot the sample mean on the x-axis of the sampling distribution
curve
If the sample mean falls within the “Do Not Reject”
region…meaning we do not have enough evidence to support
the alternative hypothesis, then the null is not rejected
If the sample mean falls in either shaded region know as the
“rejection regions,” then we have enough evidence to support
the alternative hypothesis
In Conclusion
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The only 2 statements that we can make
about the null hypothesis are that we either
reject the null hypothesis or we do not reject
the null hypothesis
Since Science can never be absolutely
“proven” only “disproven,” it is “safer” to
reject or not reject rather than accept
Example Problem
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Formulate a hypothesis statement for the
following claim: “The average adult drinks
1.7 cups of coffee per day.” A sample of 35
adults drank an average of 1.95 cups per
day. Assume the population standard
deviation is 0.5 cups. Using α = 0.10, test
your hypothesis. What is your conclusion?
Solution
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H0 : µ = 1.7 cups H1 does not = 1.7 cups
n= 35 adults; σ = 0.5 cups; α=0.10
Standard Error of the Mean: σx =σ/square root of
n=0.50/square root of 35=0.0845 cups
z=mean - µ/std error of the mean; z = +or – 1.64
Upper Limit = 1.7 + 1.64(0.0845) = 1.84 cups
Lower Limit = 1.7 – 1.64(0.0845) = 1.56 cups
Since the mean =1.95 cups, we reject the null hypothesis
and conclude that the population mean is not 1.7 cups per
day
Formulate a Hypothesis for your
Research…..
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Questions?