Semester 2

Question 1

What is the 95% confidence interval?

Answer 1

The range of valves you can be 95% sure the the mean of the population lies within

Question 2

When is the 95% confidence interval larger?

Answer 2

when more variety in population values and smaller samples

Question 3

why is 95% confidence level used?

Answer 3

to estimate precision of observed values and determine statistical significance of a difference between two differnt observations

Question 4

Describe how data should be set up in a case control study analysis

Answer 4

• top row is expose ppl bottom row is of unexposed ppl
• first column is the cases (number of outcomes) of exposed and unexposed
• 2nd column is of number of controls (no outcome)

Question 5

How is odds ratio calculated?

Answer 5

odds of outcome in exposed ppl / odds of outcome in unexposed

Can also be calculated by: a X d/ c X b or (a/b)/(c/d)

Question 6

how is error factor calculated?

Answer 6

1) 1/a+ 1/b+ 1/c +1/d = ans
2) square of ans, X 2= ans2
3) e^ans2= error factor

Question 7

How are confidence limits calculated from error factor and odds ratio?

Answer 7

OR/ error factor is lower limit

OR X error factor is upper limit

Question 8

What is the null hypothesis?

Answer 8

that there is no significant difference between the two variables and so the odds ratio is one

Question 9

1 lies within the confidence interval, is the null hypothesis accepted or rejected?

Answer 9

null hypothesis is accepted as no significant difference

Question 10

Can you ever fully reject a null hypothesis?

Answer 10

no as there is always a possibility it occurred by chance, but 5% chance is acceptable for significance of differences

Question 11

Is odds ratio relative or absolute risk?

Answer 11

relative risk- it is only comparing risk as compared to the a different population, not compared to the whole population

Question 12

How is incidence rate calculated?

Answer 12

of new events/ (# of persons x # of years)

Question 13

What is tendency?

Answer 13

the true value (observation is out best estimate of the tendency)

Question 14

Why are case control studies good?

Answer 14

• theyre quick
• theyre cheap
• theyre good for rare diseases as you can select based on outcome

Question 15

What issues are there with case control studies?

Answer 15

• selection bias (need to select control from similar population to the cases)
• information bias (make sure you do the same to both groups)
• confounding

Question 16

how can confounding be reduced in case control studies?

Answer 16

match cases with similar people who dont have disease (controls)
adjust for it in analysis by standardisation

Question 17

What are disadvantages of cohort studies?

Answer 17

• big scale
• expensive
• take long time
• survivor bias (high number of losses to follow up, healthy ppl tend to drop out)
• not good for rare outcomes
• unknown confounders cannot be accounted for

Question 18

What ratios can be used to describe relative risk?

Answer 18

• risk ratio (prevelance proportions at particular time (100 per thousand))
• rate ratio (incidence rates after a particular time (50 per 1,000 person years))
• odds ratio (odds between groups at end of time period (#dead: #alive)

Question 19

What measurements of relative risk can be applied to case control and cohort studies?

Answer 19

cohort: risk ratio, indcience rate ratio, odds ratio

case- control: odds ratio

Question 20

How would you describe the relative risk if the odds ratio for getting cancer if you smoke vs if you dont smoke is 3?

Answer 20

you are 3 times as likely to get cancer if you smoke than if you didnt