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MTBs Step 3 > Biostats > Flashcards

Biostats Flashcards

1
Q

What is the mode?

A

data point that occurs most frequently

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2
Q

What is the mean?

A

average of all the data points

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3
Q

What is the median?

A

halfway between highest and lowest value

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4
Q

What is the range?

A

distance between highest and lowest value

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5
Q

Describe a right skewed distribution and relation to mean, median & mode

A

Right skewed = tail is to the right, peak to the left

from tail –> peak: mean, median, mode

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6
Q

Define incidence

A

the rate at which new disease occur

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7
Q

Define prevalence

A

total number of cases in a population at any given time

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8
Q

Define Precision

A

data points around 1 point = points in a cluster. Doesnt mean they have to be right, just clustered

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9
Q

Define Accuracy

A

= validity. Are the points in the correct spot? *gold standard tests

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10
Q

Define Reliability in terms of tests

A

can a test outcome be reproduced

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11
Q

What % is 1 SD? 2SD? 3SD?

A 
1SD = 68%
2SD = 13.5% more (95% total)
3SD = 2.5% more (99.7% total)
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12
Q

If 40,000 students take step3 each year. The mean score is 222 with a SD of 16. How many students scored above 254? explain your answer.

A

1st how many SD above the mean is 254? (222-254)/SD(16) = 2
2nd what do they want? they want those that scored ABOVE 254 aka those that are 3SD area. 3SD = 2.5% at each tail. we want those at the tippy tippy top. ==> 2.5% of 40,000 = 1,000

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13
Q

What is the Standard Error of the Mean(SEM)?

A

a measure of how tightly grouped data is

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14
Q

What does a small Standard Error of the Mean(SEM) tell you?

A

the data is tightly grouped = more precise.

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15
Q

What is a Z-score?

A

tells you how many SD up or down from the mean the data is.

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16
Q

What is the Z-score: Average 240, SD 18. Zscore for 254?

A

254-240 = 14. 14/18(SD) = 0.78.

Zscore = 0.78

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17
Q

What is a confidence interval?

A

tells you how precise a group of data is. tells you where 95% of the data is located

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18
Q

What does it mean if a confidence interval contains 1?

A

CI contains 1 = data is not reliable, way too spread out = useless =(

19
Q

What is a correlation Coefficient(r)? What does a +r mean? -r? what if r=0?

A 
R = relation between data
R = +  positive correlation
R = - negative correlation
R = 0 no correlation
20
Q

When would you want to use a T-test?

A

when comparing 2 groups of data

21
Q

When would you want to use ANOVA test?

A

when comparing 3+ groups of data

22
Q

When would you want to use Chi-Squared test?

A

when comparing non-numerical data; are these groups related?

23
Q

What is a Randomized Controlled Trial?

A

RCT = prospective trial

*avoids many forms of bias

24
Q

What is a Cohort Study?

A

Cohort = follow the fish! ~ observes prospectively over time what happens to a group of patients with certain exposures or underlying illnesses. *used to assess risk

25
Q

What is Relative Risk? Which study type is used to calculate this?

A

RR = risk of disease based on who was exposed in the past.

*cohort studies are used to calculate this

26
Q

What is a Case Control Study? Whats the bias?

A

CCS = retrospective studies looking for the odds of a previous exposure on the development of a rare disease manifestation. (taking ppl with disease and looking for exposures)

Bias = subject to recall bias

27
Q

What is an Odds Ratio?

A

OR = those who have a disease and looking at the chance of exposure.

==> (case exposured/cases not exposed)/(control exposed/controls not exposed)

28
Q

What is Berkson Bias? How can you solve this?

A

hospitalized patient are used as trial subjects instead of the general population resulting in different results from the general population.

solution: random selection of trail subjects

29
Q

What is the Hawthorn Effect? How can you combat this?

A

those being studied know they are being studied and change their behavior.

solution: using a placebo and blinding both the investigator and the participants.

30
Q

What is lead time bias?

A

early detection is confused with increased survival

31
Q

What does it mean if a P = 0.05?

A

there is a 95% chance the ALTERNATE hypothesis is true(reject null)

32
Q

What does it mean if a P <0.05

A

Null hypothesis is rejected

33
Q

What does it mean if a P > 0.05

A

accept null

34
Q

What is a type 1 error?

A

false positive

35
Q

What is a type 2 error?

A

false negative

36
Q

What is sensitivity? How do you calculate this?

A

the likelihood a test will detect all the ppl with the disease.

TP/(TP + FN) = sensitivity

37
Q

What is specificity? How do you calculate this?

A

the likelihhood that ppl without a disease are correctly identified as disease negative

TN/(TN+FP) = specificity

38
Q

What is NPV? How do you calculate this?

A

If the test is negative, what is the likelihood you really dnt have the disease?

TN/(TN+FN) = NPV

39
Q

What is PPV? How do you calculate this?

A

If the test is positive what is the likelihood you really do have the disease?

TP/(TP+FP) = PPV

40
Q

What is Absolute Risk Reduction(ARR)?

A

% decrease in the risk of death or disease from a treatment compared to 100% of ppl in a population

ex: 3% no tx vs 2 % with tx arr=1%

41
Q

What is Number Needed to Treat(NNT)? How do you calculate this?

A

NNT = 1/ARR ~number of ppl you have to treat to save 1 life

42
Q

What is the Number Needed to Harm(NNH)? How do you calculate this?

A

NNH = number of ppl you have to treat to harm 1 person.

NNH = 1/Absolute Risk

Absolute Risk = incidence w/exposure - incidence without exposure

43
Q

How do you calculate Absolute Risk?

A

Incidence with exposure - incidence without exposure

MTBs Step 3 (30 decks)

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