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FOS 2 > Biostats > Flashcards

Biostats Flashcards

1
Q

What is epidemiology?

A

The study of factors that determine the occurrence and distribution of a disease in a population

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2
Q

What is incidence?

A
  • Frequency of occurrence of disease
  • Number of new cases over course of study
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3
Q

What is prevalence?

A
  • The number of people who have the disease over a given period of time or at a given point in time
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4
Q

What is the mathematical relationship between incidence and prevalence?

A

Prevalence = Incidence * Avg. Duration

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5
Q

What are 2 factors that would cause the prevalence to decrease?

A

A person in the study dies

A person in the study is cured

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6
Q

How do you determine point prevalence?

A

Count the # of cases on a given date and divide by the total # of people in the population. Account for any who have died by subtracting from the total population.

Ex: A community started out with 20 people on October 1st 2004. Six people in the community are sick with HIV on April 1st 2005 and 2 people died between October 1st 2004 and April 1st 2005. The point prevalence is 6 / (20-2) = 6/18 = 33%

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7
Q

How do you calculate the period prevalence?

A

Incidence / Initial population size

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8
Q

What factors result in a high prevalence?

A

High incidence

High survival rates

High detection rate

Rapid fatality

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9
Q

What factors contribute to low prevalence?

A

Low incidence

High cure rate

Short disease course

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10
Q

What are risk events?

A

Events that put people at risk for the disease of interest over the course of a study

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11
Q

What is attributable risk?

A
  • The additional incidence, above baseline, that is caused by the risk factor.
  • The incidence of the disease in people that were exposed to a specific risk factor - incidence in people that were not exposed to that risk factor
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12
Q

What is absolute risk?

A

The absolute risk of getting a disease is equivalent to the incidence of the disease

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13
Q

What is relative risk?

A

The ratio of the proportion of events that occur in one group compared to the number that occur in another group

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14
Q

Relative risk can only be measured in what kind of study?

A
  • A prospective study - finds naturally occurring cohorts in the present and follows them into the future
  • To measure relative risk we prospectively study cohorts that are differently exposed to the risk factor.
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15
Q

What is relative risk reduction?

A

RRR = 1 - RR

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16
Q

What is absolute risk reduction?

A
  • The difference between the absolute risk rate of the placebo and the drug groups
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17
Q

What is the number needed to treat and what does it tell you about a treatment?

A
  • NNT = 100/ARR
  • Tells you the effectiveness of different treatments; tells you the number of people who would need to receive the treatment in order for 1 life to be saved
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18
Q

What is the absolute risk increase?

A

Risk (treatment) - Risk (control)

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19
Q

What is the number needed to harm?

A

NNH = 100/ARI

Reflects the number of people that would need to receive the drug before 1 person would experience negative side effects

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20
Q

What is the odds ratio?

A

The odds that a person with the disease (case) was exposed to the risk factor / the odds that a person without the disease (control) was exposed to the risk factor

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21
Q

When is an odds ratio used?

A

In a retrospective study only (case-control study)

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22
Q

What does an odds ratio of 1 mean?

A

That the odds of prior exposure were the same in both groups of people

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23
Q

What is the hazard rate?

A

The rate at which an event occurs –> the likelihood that a person will be exposed to a hazardous event over a gien period of time

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24
Q

What is a Kaplan - Meier curve used to represent?

A

Survival data

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25
Q

What are the 3 major categories of study design?

A

Experimental design

Quasi-experimental design

Observational Design

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26
Q

Describe an experimental study.

A

In experimental studies, researchers manipulate a variable (independent variable) and measure the effect of this manipulation on a specific factor or factors (dependent variable(s))

27
Q

The _____ variable is the one that the researchers control.

A

Independent

28
Q

The _____ variable is the one being measured.

A

Dependent

29
Q

What is a quasi-experimental study?

A

One where subjects are not randomized to the treatment groups.

30
Q

What is an observational study?

A

One where researchers observe what happens without making any manipulations.

31
Q

What is a cohort study and what kind of study is it?

A

This is a non-experimental or OBSERVATIONAL study

A cohort study is when you identify groups of people who have been exposed or unexposed to a risk factor and then begin the study to see how many of them develop disease in each group.

32
Q

A cohort study is (retrospective or prospective).

A

Prospective

33
Q
  • What is a historical cohort study?
  • What type of study is this?
  • Is it prospective or retrospective?
A
  • You begin by identifying people who either have or have not developed disease and then try to correlate that to exposure to a known risk factor.
  • Observational
  • Retrospective
34
Q
  • What is a case-control study?
  • What type of study is this?
  • Is it prospective or retrospective?
  • What is the difference between a case-control study and a historical cohort study?
A
  • You begin by identifying people who either have (case) or do not have (control) the disease. You then try to determine if they were exposed to a risk factor that contributed to their condition.
  • Observational
  • Retrospective
  • The difference between this and a historical cohort study is that in case-control the risk factor is not known and you are trying to determine what that risk factor is. In a historical cohort, the risk factor is known and you are trying to determine the extent to which it contributed to disease development.
35
Q
  • What is a case series study?
  • What type of study is this?
  • Is it prospective or retrospective?
A
  • A group of people are exposed to a risk factor and develop a known disease. You then just describe the presentation of the disease.
  • Observational
  • Retrospective
36
Q

What is a case report?

A

A special kind of case series study where the presentation is only of a single patient.

37
Q
  • What is a prevalence survey?
  • What type of study is this?
  • Is it prospective or retrospective?
A
  • You identify individuals in whom a disease is either present or absent and assess the prevalence of that disease. You do not know whether exposure to a risk factor occurred or not.
  • Observational
  • Retrospective
38
Q
  • What is a cross-sectional study?
  • What kind of study is this?
  • Is this prospective or retrospective?
A
  • You examine the exposure to the risk factor and the disease status at the same time and you do it only at a single point in time.
  • Observational
  • Retrospective
39
Q
  • What is a longitudinal study?
  • What type of study is this?
  • Is it retrospective or prospective?
A
  • Cross-sectional studies in which the disease status of participants is repeatedly measured over a period of time to assess disease trends
  • Observational
  • Retrospective
40
Q
  • What is an ecological study?
  • What type of study is this?
A
  • Studies in which the unit of analysis is a population rather than an individual
  • Observational
41
Q
  • What is a quantiative study?
  • What is a qualitative study?
A
  • The amount of the dependent variable is measured
  • You assess the quality of the subjects responses to surveys or queries
42
Q

In general, a longitudinal study is weaker than a cross-sectional study.

True/False

A

False

43
Q

In general, a prospective study is stronger than a retrospective study.

True/False

A

True

44
Q

What is the only type of experimental study we learned about?

A

Randomized control trial

45
Q

Order the types of observational studies from least strength in hypothesis generation to most strong.

A

LEAST

Descriptive study

Ecological study

Cross-sectional study

Case-control study

Cohort study

MOST

46
Q

What are the pros and cons of qualitative research?

A

Pros:

  • Potential to generate hypotheses
  • In participant’s own language

Cons

  • Cannot test hypotheses
  • Explore only what is stated by participants
  • Potential for bias
47
Q

What are the pros and cons of cross-sectional surveys?

A

Pros

  • Quick and easy
  • Useful for hypothesis generation

Cons

  • No evidence of relationship between risk factors and disease
  • Subject to bias
  • Not good for hypothesis testing
48
Q

What are the pros and cons of a cohort study?

A

Pros

  • Can be retrospective or prospective
  • Can be used to obtain absolute measure of risk
  • Good for studying rare risk factors

Cons

  • Time consuming and costly
  • Study only risk factors measured at beginning
  • Only appropriate for common diseases
  • Loss to followup
49
Q

What are the pros and cons of case-control studies?

A

Pros

  • Quick and easy
  • Study many risk factors
  • Good for studying rare disease

Cons

  • Only relative measure of risk can be obtained
  • Recall bias
  • Control selection may be difficult
  • Only study one disease at a time
50
Q

What are the pros and cons of randomized control trials?

A

Pros

  • Gold standard for evaluating treatment or preventative interventions
  • Extensive control over research process

Cons

  • Time consuming and costly
  • Can only study interventions or exposures that are controlled by investigator
  • Limited generalizability
  • Often unethical
51
Q

What are the pros and cons of ecological studies?

A

Pros

  • Quick and easy
  • Useful for hypothesis generation

Cons

  • Do not allow for causal conclusions
52
Q
  • What is bias?
  • What does bias produce?
A
  • A process at any stage of inference tending to produce results that depart systematically from the true values
  • Deviations and distortions that tend to go in one direction
    *
53
Q

What are the 2 categories of bias?

A
54
Q

What is assembly bias?

A

When the groups being compared are not equally susceptible to the outcome of interest for reasons other than the factor under study

55
Q

What is allocation bias?

A

Allocation bias is when the investigator chooses a non-random method of assigning subjects to study groups.

56
Q

What is selection bias?

A

Occurs when subjects are allowed to select the study group they want to be in.

57
Q

What is detection bias?

A

The result of failure to detect a case of disease, a possible causal factor, or an outcome of interest. It can be caused by the use of a particular diagnostic technique or type of equipment.

58
Q

What is measurement bias?

A

Occurs when the method of measurement leads to systematically incorrect results.

59
Q

What is confounding?

A

Occurs when we are trying to find out whether a factor is a cause of disease in and of itself. If the factor of interest is associated with another factor, which itself is also related to the outcome, the effect of the factor under study can be confused or distorted by the effect of the other factor.

60
Q

When can you control for confounding?

A

Before a study begins by restriction (narrowing down the group of people you are recruiting for the study to reduce known confounding as much as possible)

After a study is done (in the analyses by matching, stratification, and standardization)

61
Q

How do you minimize the effect of bias and unknown confounding in a study?

A

Randomization

62
Q

Although it reduces the contribution of known confounders, what are the drawbacks to doing pairwise matching?

A

Recruitment can be cumbersome

You cannot examine the effect of a matched variable

63
Q

What is stratification?

A

It allows the association between exposure and outcome to be examiend within different strata of the confounding variable

64
Q

What is standardization?

A

Takes into account differences in characteristics between 2 populations. It allows for adjustment needed to negate the effects of a variety of confounding factors.

FOS 2 (44 decks)

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