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SoBe II > Biostats -- Beehler > Flashcards

Biostats -- Beehler Flashcards

1
Q

What concepts measure the frequency of a disease in a population?

A

Prevalence, incidence, attack rate

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2
Q

What concepts determine how well a test differentiates sick from healthy people?

A

Sensitivity, Specificity

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3
Q

What concept determines how many in a population are truly sick of those that test sick or healthy?

A

Predictive Value

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4
Q

What concepts determine the impact of a medicine/treatment?

A

Risk reduction/increase, number needed-to-treat/harm

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5
Q

Define Prevalence.

A

Prevalence = number of people with a disease at a specific point in time / number of people AT RISK for the illness at that point in time

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6
Q

What is point prevalence?

A

Prevalence during a period of time

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7
Q

What is lifetime prevalence?

A

Prevalence over the course of a lifetime

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8
Q

A county in Minnesota has a population of 1,500. In 2013, 180 individuals were diagnosed with type 1 diabetes. Last year, 30 individuals were diagnosed with it. What is the prevalence of type 1 diabetes in this population in 2014?

A

Prevalence = (180+30)/1500 = 210/1500 = 0.14

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9
Q

Define Incidence.

A

Incidence = number of NEW people with the disease during a time period / number of people AT RISK for illness during that time period

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10
Q

What is cumulative incidence?

A

Total number reported over time

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11
Q

What is the attack rate vs. secondary attack rate?

A

Attack rate = number of new cases / number exposed

Secondary attack rate = number of new cases / (number exposed - primary cases)

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12
Q

A county in Minnesota has a population of 1,500. In 2013, 180 individuals were diagnosed with type 1 diabetes. Last year, 30 individuals were diagnosed with it. What was the incidence of type 1 diabetes in this population in 2014?

A

Incidence = 30/(1500-180) = 30/1320 = 0.023

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13
Q

Define Attack Rate.

A

Type of incidence used when nature of disease is acute & population observed for short period of time (e.g., outbreaks, specific exposures)

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14
Q

Within a kindergarten class, 5 of 35 kids develop chicken pox during a 1-week period. In the next two weeks another 10 kids also come down with chicken pox. What are the attack and secondary attack rates of chicken pox in the classroom?

A

Attack = (5+10)/35 = 15/35 = 0.43

Sec. Attack = 10/(35-5) = 10/30 = 0.33

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15
Q

What affects prevalence and incidence?

A

Duration of illness (longer -> higher prevalence)
Number of new cases (more new cases -> higher prevalence)
Migration
In-migration (ill -> higher prevalence)
Out-migration (well -> higher prevalence)
Recovery & death -> lower prevalence
Prevention -> lower incidence
Changes in diagnostic criteria or reporting

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16
Q

What is the relationship between prevalence and incidence?

A

Prevalence > incidence if disease is long term (e.g., diabetes)

Prevalence ≈ incidence if illness is acute (e.g., flu)

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17
Q

Define Sensitivity.

A

The probability that a diseased person will be identified correctly by a diagnostic/screening test (AKA true-positive probability or true-positive rate)

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18
Q

What are true positives?

A

Ill people identified as ill

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19
Q

What are false negatives?

A

Ill people identified as well

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20
Q

What is sensitivity?

A

Sensitivity = true positives / total number of ill people (true positives + false negatives)

21
Q

A group of individuals who were exposed to Lyme disease were screened using a new test developed for early detection. Of the 344 screened, the disease was confirmed in 258. The new test detected 263 cases of Lyme disease, 32 of which were disconfirmed. What is the sensitivity of the new test?

A

Sensitivity = True positives / total # ill = 231/258 = 0.90

22
Q

Define Specificity.

A

The probability that a well (non-diseased) person will be identified correctly by a diagnostic/screening test (AKA true-negative probability)

23
Q

What are true negatives?

A

Well people identified as well

24
Q

What are false positives?

A

Well people identified as ill

25
Q

What is specificity?

A

Specificity = true negatives / total number of well people (true negatives + false positives)

26
Q

A group of individuals who were exposed to Lyme disease have been screened using a new test developed for early detection. What is the specificity of the new test?

A

Specificity = true negatives / total number of well people = 54 / 86 = 0.63

27
Q

High Sensitivity test err on the side of _________________.

A

Over-diagnosing: identifying most or all possible disease cases.
Most useful when under-diagnosing may lead to severe consequences (fast-developing cancers)

28
Q

High Specificity test err on the side of _________________.

A

Under-diagnosing: identifying most or all well people.

Most useful when over-diagnosing may lead to dangerous, painful, or unnecessary treatment.

29
Q

If negative is a lower score and positive is a higher score, then lowering the cutoff will increase the _______. and decrease the _______.

A

Sensitivity

Specificity

30
Q

Define Predictive Value.

A

Probability that a test will give the correct diagnosis, which depends on sensitivity, specificity, and prevalence of the disease in the population being tested.

31
Q

What is positive predicted value?

A

Probability that a person who tests positive for a disease truly have it.
PPV = true positives / all positives (true + false positives)

32
Q

What is negative predicted value?

A

Probability that a person who tests negative for a disease truly is well.
NPV = true negatives / all negatives (true and false negatives)

33
Q

With higher disease prevalence, what happens to the PPV and NPV?

A

Higher PPV = greater chance that a positive test reflects true illness.
Lower NPV = lower chance that a negative test reflects disease-free state.

34
Q

With lower disease prevalence, what happens to the PPV and NPV?

A

Lower PPV = lower chance that a positive test reflects true illness.
Higher NPV = higher chance that a negative test reflects disease-free state.

35
Q

What are randomized controlled trials?

A

They have at least one treatment group and one control group with people in both groups responding either positively or negatively.

36
Q

What is the control event rate (CER)?

A

Proportion of control group participants who have a bad outcome after “treatment”

37
Q

What is the experimental event rate (EER)?

A

Proportion of treatment group participants who have a bad outcome after treatment

38
Q

What is the absolute risk?

A

Absolute risk or risk difference is the difference in risk of developing a disease or undesired outcome after treatment
= |control event rate - experimental event rate| = |CER - EER|

39
Q

What is absolute risk reduction?

A

Higher rate of adverse outcomes in control group when CER > EER

40
Q

What is absolute risk increase?

A

Higher rate of adverse outcomes in treatment group when CER

41
Q

What is relative risk?

A

Relative risk or risk ratio is the proportion of treatment group risk to control group risk
= experimental event rate / control event rate = EER / CER

42
Q

What is relative risk reduction/increase?

A

difference in 2 event rates, as a proportion of the event rate in the control group
RRR/RRI = 1-RR = AR/CER
Reduction: CER > EER
Increase: CER

43
Q

After participating in an RCT of a new cancer drug, 10 of 30 control group participants become sicker and 4 of 30 treatment group participants become sicker. Did the new treatment reduce or increase absolute risk? By how much?

A

CER – EER = 10/30 – 4/30 = .33 - .13 = .20 =

20% reduction

44
Q

After participating in an RCT of a new cancer drug, 10 of 30 control group participants become sicker and 4 of 30 treatment group participants become sicker. Did the new treatment reduce or increase the risk of illness relative to the control group? By how much?

A

1 – RR = 1 – EER/CER = 1 - .13/.33 = 1 - .39 = .61 = 61% reduction

45
Q

What is number needed to treat (NNT)?

A

Number of patients who need to be treated to get 1 additional patient a favorable outcome
NNT = 1/ARR

46
Q

What is number needed to harm (NNH)?

A

Number of patients who, if they were treated, would result in 1 additional patient being harmed
NNH = 1/ARI

47
Q

What do NNT and NNH depend on?

A

Condition, Severity, and Outcome

48
Q

In a study,200 patients received a new drug to slow the progression of Parkinson’s and 300 patients did not receive the medication. 20 patients in the treatment group and 60 patients in the control group had a typical progression of Parkinson’s. What is the absolute risk reduction and number needed to treat?

A 
CER = 60/300 = .2
EER = 20/200 = .1
ARR = CER - EER = .1
NNT = 1/ARR = 1/.1 = 10

SoBe II (12 decks)

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