My Biostats Ppt

7/28/2019 My Biostats Ppt

1/11

Epidemiology


2/11

Now, an unrelated note

epidemiology review

Prevalence all cases of a disease in a population =total # of existing cases / number in total population

Incidence all NEW cases of a disease in a susceptiblepopulation (not susceptible population in both) =number new cases / susceptible population

What decreases/increasese prevalence?

Cures (common cold)?

High mortality rate? (pancreatic cancer)

Good treatment but not cures (AIDS)?


3/11

Sensitivity and Specificity

Sensitivity ability of a test to identify

individuals who have the disease;

Specificity ability of a test to identifyindividuals who do not have the disease;


4/11

Risk Reduction

Relative Risk the ratio of risks b/w 2 groups (usually acontrol and experimntal); = incidence therapy group (It) /incidence control group (Ic)

Relative Risk Reduction the percent decrease of risk b/w

2 groups = 1-RR = (Ic It) / Ic Absolute Risk Reductiondifference in risk between two

groups = Ic-It

Number Needed to Treat- number of patients that must betreated to prevent one occurrence of the disease = 1/ARR

Thinking about them in terms of pharmaceuticals is reallyhelpful in understanding why you need these terms!


5/11

Sensitivity refers to the # of true positivesdivided by the total number of patients w/ thedisease.

Sensitivity = a/(A+C) Screening tests need to have HIGH sensitivity in

order to pick up all cases of the disease (decreasefalse negatives)

False negative ratio: 1- sensitivity

Not affected by disease prevalence


6/11

Calclate Odds Ratio

ratio, all values were not given in tables, uhave to

make ur own table and understand where in

the q stem u have to pick the valuesvery imp!! Lots ofqsthis is

not difficult and

worth knowing this..of coursefor everythingsensitivity,

specificity, PPV, NPV etc


7/11


8/11

Power


9/11

Q about Chlamydia in students, prevalence

decrease /increase of

what? (options incl they treat more pts, less

awareness (dontrememberexactlyso they

described u several situations that might

cause these changesso u need to understand

what they r talking about, very HYepidemiology/stats!)


10/11

Probability

Total probability always = 1.0 or 100%

Probability (at least 1 positive) = 1- Probability (allnegative)

Prevalence = Incidence x Time

Incidence is NOT changed by treatment

Treatment that PROLONGS survival but does not curedisease will Prevalence due to an number afflicted

Incidence = new cases diagnosed over period of time

Prevalence total cases at a particular point in time


11/11

Stats Tests

Means (between 2 groups): T-tests

Means (between more than 2 groups): ANOVA

% or proportions (between 2 or more groups):

Chi Square

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My Biostats Ppt