ANTC67 Mar 8 Lec.doc

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2 Apr 2012
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ANTC67Lec 8
eg smoking (exposure factor) is a medical condition
What would expose people to a certain entity that would decrease or increase rate
of smoke?
Lung cancer (disease condition)
Eg autism (condition)
What exposure factor is considered to give rise to the condition
Vaccine
Eg diabetes (condition)
What exposure factor contributes to elevation of diabetes
Obesity
Eg breast cancer
Eg estrogen pills
Breast feeding could lower the rate of breast cancer
Have matrix
Always +/- (disease present or not)
Then exposure (yes and no)
Then have high middle low income classes?
Odds ratio: (a*b / b*c)
If the value is around 1 then no relationship, no association
But before can interpret what Odds ratio is, we have to look at Chi Square
Because chi square says ‘highly sig’ means that this relationship is stsistically sig
Eg breast cancer (y/n), child (y/n), breastfeed (y/n), how many children (y/n) (across)
Names of women going down
Hypothesis is basically the question
Null hypothesis (Ho) (no relationship)
Is there a relationship, which is H1
So we’ll be using chi square to test our odds ratio
Region of rejection: how much error are you willing to let into your decision
How confident are you that you made the right decision
Alpha is typically 0.5, so 0.5% error, and we allow this because we are always dealing with
samples
Degrees of freedom= (rows-1)*(columns-1)
If in the assignment there is a percentage, convert that percentage into a whole number
No cell in matrix should be zero
But can put in decimal points?
MH chi square: MH stands for Mantel and Haenezel
Formulas are on the exam
Common rule of thumb is that in a b c d should not drop below 5, so staticians let it even
go down to 1
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