Lecture bioinformatic databases - Thursday

16 important questions on Lecture bioinformatic databases - Thursday

What are other names for follow up studies?

Longitudinal study or cohort study

The aim of the follow up / cohort study is ...

To measure the occurence of one or more specific diseases during the period of follow up. Usually with the aim of comparing the disease rates between two or more (exposure) groups

--> estimate association between exposure and outcome

What are exapmles of outcome in a study?

Disease, death, birth defect or costs
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What are examples of exposure in studies?

Medication use, environmental factor, SNP, condition and procedure

How do you indentificate exposure groups?

1. Self selection (natural distribition or risk factor = BMI)
2. Selection by researcher (rare risk factors) = not common
--> researcher search for people in exposure group
3. Selection by chance

What is the difference between an observational and experimental follow up study?

Experiment - randomised controlled trial, so exposure is randomly allocated

Observational - exposure is fixed, determined by participants or circumstances

What are the pros and cons of prospective studies?

Pro: control data collection
Con: time-consuming / expensive

What are two types of study populations?

Closed and open/dynamic cohorts

What is the difference between closed and open/dynamic cohorts?

Closed: no replacements, only losses, so this cohort becomes smaller and smaller

Dynamic: losses and replacements, same number of people (dynamic stationary population)

How do you calculate the cumulative incidence?

1. Directly - for equal follow up duration
2. Via life table (Kaplan-Meier) - takes unequal follow up duration into account
3. From incidence rate - linear approximation / exponential approach

What is the cause of unequal lenghts of follow up?

1. Loss of follow-up
2. Unequal starting times
3. Withdrawn alive 

-> solved by Kaplan Meier method

What is the difference between withdrawn alive and lost to follow up (LtFU)?

Withdrawn alive is when the end of the study is reached --> result is censoring, independent of outcome
Loss to follow up =  dependent on outcome, probably due to sickness or recovery -> influences study

How do you calculate the rate ratio and risk ratio for the absolute risk?

Rate = ci / Ni * ti
Risk = ci / Ni

How do you calculate the absoulte rate difference?

Exposed - unexposed = c1 / N1*t1 - c0/N0*t0

How do you calculate relative risk (RR)?

RR = RA / Rb

-> Ra = absolute risk group A (exposed)
-> Rb = absolute risk group B (not exposed)

How do you calculate the relative risk reduction (RRR)?

1-RR * 100%

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