Hypothesis
Tesitng: TTest Example

Example: Eyespot
Data 
Many accounts suggest that many species of animals
find direct stares from another animal aversive.
Some moths have developed eyespot patterns on their
wings or bodys to ward off predators. An experiment
was done using 16 motheating birds. These birds
were tested in a twochambered box that they were
free to roam in from side to side. One chamber had
two eyespot patterns painted on the wall. The other
chamber had plain walls. Each bird was left in the
chamber for 60 minutes, and the amount of time spent
in the plain chamber was recorded.

Here are the four steps involved in the statistical
hypothesis test:
 State the Hypotheses: The null hypothesis
is that there is no effect for eyespots painted
on the wall. Birds should spend half their time
 30 minutes  in each room. The alternative
hypothesis is that there is an effect. In symbols
the null and alternative hypotheses are:
 Set the decision criteria: We arbitrarily
decide on an alpha level
We also note that there are 15 degrees of freedom:
The table tells us that the critical region consists
of t values less than 2.131 and greater than
+2.131.
 Gather Data:
Results:
The mean is 35 minutes in the plain side, and
the sample variance is 81.
 Evaluate Null Hypothesis:
Calculations:
The formula for the estimated standard error is:
For these data, the estimated standard error is
Sqrt(81/16) = 2.25
The formulat for T is:
Thus, for these data, T = (3530)/2.25 = 2.22
Decision:
Since 2.22 is in the critical region, we reject
the null hypothesis that the presence of eyespot
patterns does not influence behavior.

ViSta Applet
Report for the Eyespots Data.


 Two more ViSta examples
 ZTest: Inclass survey SAT Math and Verbal data (pop
mean=460, pop stdv=100). ViSta
Data
Report for the SAT Verbal Variable 

Report for the SAT Math Variable 

 TTest: Newcomb Lightspeed
ViSta Data
These data are from the first experiment to determine
the speed of light. The best modern measurements correspond
to a passage time of 33.02 in this experiment. The population
standard deviation is unknown.
Report for the Newcomb Lightspeed Data 

