Transcript Elise`s Seminar

Decreased Rate of Coronary
Restenosis After Lowering of
Plasma Homocystine Levels
Seminar 25
Elise Miller
A few definitions….
• Plasma Homocystine- blood amino acid
influenced by genetics and diet.
• Restenosis- renarrowing of an artery after
angioplasty caused by fat or cholesterol
buildup.
• Angioplasty- opens blocked arteries by the
inflation of a tiny balloon.
Which Alternative Makes
Sense?
Luminal Diameter:
Ha: µF>µP
↑
Stenosis:
Ha: µF>µP
Ha: µF<µP
Ha: µF<µP
↑
Late Loss Luminal Diameter:
Ha: µP>µF
Ha: µP<µF
↑
T-test Construction
• When dealing with two means and
unequal sample sizes:
Degrees of Freedom
• Large, complicated formula….
d.f.= (s12/n1 + s22/n2) ÷ (((s12/n1)2 ÷ (n11)) + ((s22/n2)2 ÷ (n2-1)))
• For our purposes it is assumed that
df=160
(somewhere between n1-1 and n1+n2-2)
Practice
• Find the T-statistic for Luminal Diameter
• Given info:
Folate Group: sample n= 92
sample mean= 1.72
sample s.d= .76
Placebo Group: sample n=85
sample mean=1.45
sample s.d= .88
Plug in the values…
(1.72-1.45)/sqrt[(.76^2/92)+(.88^2/85)]
t=2.1765
• This value gets inputted into Minitab to
easily find the P-value.
T-Values
• Luminal Diameter:
T=2.1765
• Stenosis:
T=-2.226
• Late Loss Luminal Diameter:
T=-1.860
Reasoning…
• Luminal Diameter:
-positive value, wider arteries
are better
• Stenosis:
-Negative value, after treatment the severity of
stenosis decreased.
• Late Loss Luminal Diameter:
-Negative value, control is being compared to
treatment group
-the negative shows that the luminal
diameter was smaller in the control
group.
What about the P-values?
• Based on the t-statistics, what may the
p-values be? (large n value)
• Luminal Diameter:
T=2.1765
• Stenosis:
T=-2.226
• Late Loss Luminal Diameter:
T=-1.860
P-value Comparisons
• Luminal Diameter:
given: p=.02
by hand: p=.0155
• Stenosis:
given: p=.01
by hand: p=.01371
• Late Loss Luminal Diameter:
given: p=.03
by hand: p=.0324
Potential Bias?
• Most studies published in medical
journals tend to have little or no bias
• A few people did drop out of the study,
but most likely did not create any
impact on the results.
Research Conclusions
• Folate treatment is beneficial compared
to placebo treatment group.
• Treatment reduced restenosis, and late
loss luminal diameter.
• Treatment increased luminal diameter
post-op.