<p>I have been dying to verify the answers for the stats exam. especially question number 2. anyone remember how to do this question?? as well as others. i would like to verify my answers for every question make sure i was heading in the right direction. thanks.</p>
<p>what exactly was the question again</p>
<ol>
<li>The ELISA tests whether a patient has contracted HIV. The ELISA is said to be positive if it indicates that HIV
is present in a blood sample, and the ELISA is said to be negative if it does not indicate that HIV is present in a
blood sample. Instead of directly measuring the presence of HIV, the ELISA measures levels of antibodies in the
blood that should be elevated if HIV is present. Because of variability in antibody levels among human patients,
the ELISA does not always indicate the correct result.
As part of a training program, staff at a testing lab applied the ELISA to 500 blood samples known to contain
HIV. The ELISA was positive for 489 of those blood samples and negative for the other 11 samples. As part of
the same training program, the staff also applied the ELISA to 500 other blood samples known to not contain
HIV. The ELISA was positive for 37 of those blood samples and negative for the other 463 samples.
(a) When a new blood sample arrives at the lab, it will be tested to determine whether HIV is present. Using the
data from the training program, estimate the probability that the ELISA would be positive when it is applied
to a blood sample that does not contain HIV.
(b) Among the blood samples examined in the training program that provided positive ELISA results for HIV,
what proportion actually contained HIV?
(c) When a blood sample yields a positive ELISA result, two more ELISAs are performed on the same blood
sample. If at least one of the two additional ELISAs is positive, the blood sample is subjected to a more
expensive and more accurate test to make a definitive determination of whether HIV is present in the
sample. Repeated ELISAs on the same sample are generally assumed to be independent. Under the
assumption of independence, what is the probability that a new blood sample that comes into the lab
will be subjected to the more expensive test if that sample does not contain HIV?</li>
</ol>
<p>also there was question</p>
<ol>
<li>A manufacturer of toxic pesticide granules plans to use a dye to color the pesticide so that birds will avoid eating
it. A series of experiments will be designed to find colors or patterns that three bird species (blackbirds, starlings,
and geese) will avoid eating. Representative samples of birds will be captured to use in the experiments, and the
response variable will be the amount of time a hungry bird will avoid eating food of a particular color or pattern.
(a) Previous research has shown that male birds do not avoid solid colors. However, it is possible that males
might avoid colors displayed in a pattern, such as stripes. In an effort to prevent males from eating the
pesticide, the following two treatments are applied to the pesticide granules.
Treatment 1: A red background with narrow blue stripes
Treatment 2: A blue background with narrow red stripes
To increase the power of detecting a difference in the two treatments in the analysis of the experiment, the
researcher decided to block on the three species of birds (blackbirds, starlings, and geese). Assuming there
are 100 birds of each of the three species, explain how you would assign birds to treatments in such a block
design.
(b) Other than blocking, what could the researcher do to increase the power of detecting a difference in the
two treatments in the analysis of the experiment? Explain how your approach would increase the power.</li>
</ol>
<p>also question one
- As gasoline prices have increased in recent years, many drivers have expressed concern about the taxes they pay
on gasoline for their cars. In the United States, gasoline taxes are imposed by both the federal government and
by individual states. The boxplot below shows the distribution of the state gasoline taxes, in cents per gallon,
for all 50 states on January 1, 2006.
(a) Based on the boxplot, what are the approximate values of the median and the interquartile range of the
distribution of state gasoline taxes, in cents per gallon? Mark and label the boxplot to indicate how you
found the approximated values.
(b) The federal tax imposed on gasoline was 18.4 cents per gallon at the time the state taxes were in effect.
The federal gasoline tax was added to the state gasoline tax for each state to create a new distribution of
combined gasoline taxes. What are approximate values, in cents per gallon, of the median and interquartile
range of the new distribution of combined gasoline taxes? Justify your answer.</p>
<p>median was estimated a 20.8 and IQR 7.2</p>
<p>What did you do… write the questions down and such… honestly, I cant help because I did not take form B, but seriously, you should know how to do those, they seemed VERY EASY to me, assuming you showed ALL WORK!</p>
<p>question 2 i didnt know how to do. if you know how to do it can you help. and question one since the median was 20.8 i added 18.4 to the median bc 18.4 federal tax was added to the state tax. so wouldnt the median increase by 18.4 as well as the IQR? thats how i approached question one. and question 4 i said that for part a you use random numbers table number each species and for eahc species 50 would go in each treatment. but part b got me because i said that the other way you can increase power is by replicating experiement??? im not sure if thats entirely right…i know you didnt do form b but if its easy could you shed some light on me :(?</p>