All sections for Final Flashcards

Question

Cross-sectional studies and causality

Answer 1

Cross-sectional studies are not enough to determine causality. Only mathematical associations Case-Control designs are the next step in order to determine causality. - They themselves do not conclusively determine causality.

Answer 2

Cross-sectional studies are not enough to determine causality. Only mathematical associations Case-Control designs are the next step in order to determine causality. - They themselves do not conclusively determine causality.

Answer 3

Relatively feasible and not too time-consuming Relatively inexpensive to conduct Helps to estimate burden of diseases within a population - Useful for health planning We can study multiple outcomes/exposures at once - Demographics of the people they occurs in/does not occur in - Conditions in which the health outcomes/exposures occurs - What exposures are near the outcome at the time that the snapshot was taken. Prompts further research

Answer 4

Can establish an association, but NOT causation - Temporal relationship between exposure and outcome may be difficult to establish VERY susceptible to bias - Impossible to ensure that confounders are distributed equally among the groups - Often either exposure or outcome or both depend upon recall, which is fallible - Groups could have different sample sizes, resulting in loss of statistical efficiency Weaknesses of using aggregated data. - Ecological Fallacy: Ecological inference fallacy or Population fallacy - EX: falsely assumes that every individual's IQ is high, since the class average IQ is high Occurs when inferences about the nature of individuals are deduced from inferences about the group to which those individuals belong.

Answer 5

Observational – there is no manipulation of events/variables.

Answer 6

- Can study multiple outcomes/exposures - Inexpensive, feasibility, not too time-consuming - Helps to estimate burden of disease - Prompts further research

Answer 7

- Cannot determine causality - May not be generalizable - Susceptible to other bias (confounders, recall, sample size)

Answer 8

the possible relation of an exposure to a certain disease - We identify a group of individuals with that disease or outcome of interest called (cases) - For comparison, a group of people without that disease or outcome of interest (controls)

Answer 9

to determine the proportion of exposure in each group

Answer 10

the prevalence of exposure should be higher in cases (disease) than in controls (no disease).

Answer 11

1. definition of cases 2. selection of cases 3. selection of controls 4. ascertainment of exposure status 5. analysis 6. conclusion and interpretation

Answer 12

Be specific - what type of ling cancer? - level of severity - how long have they been diagnoses - clinical characteristics cases should be representative of all disabled Correctly defining cases (outcome) helps us to select the cases and limit bias.

Answer 13

Selecting our cases is important because it can introduce bias. What is bias? “systematic error introduced in to sampling or testing by selecting or encouraging one outcome or answer over another.” Lots of different types Bias is not always purposeful

Answer 14

selection of individuals, groups, or data for analysis in such a way that the sample is not representative of the population intended to be analyzed. sources - hospital patients, physicians practice patients, clinic patients, disease registries

Answer 15

- some tertiary and quarternary care facilities selectively admit severely ill patients - Risk factors only in individuals with severe forms of the disease - Not generalizable to all patients with the disease if used would need to select from several hospitals in the community

Answer 16

- Quarternary (experimental medicine and uncommon specializations) - Tertiary (hospitalization and higher specialization like neurosurgery) - Secondary (specialists like cardiologists, oncologists, ect.) - Primary (essentials of screening, illness, injury, referral

Answer 17

- Must often wait for new cases to be diagnosed - Prevalent cases have already been diagnosed and represent a larger number of cases available for the study Tub example - prevalence is in the tub - mortality (death) is the drain - recovery is evaporation - incidence is the faucet

Answer 18

Risk factors that we identify in a study using prevalent cases may be related more to survival with the disease rather than to the development of the disease Such a study is more likely to include longer-term survivors. Non-representative group of cases

Answer 19

One of the most difficult problems in epidemiology. If we find more exposure in the cases than in the controls - Would like to conclude that there is an association between the exposure and the disease. The way controls are chosen is a major determinant of whether this conclusion is valid. Fundamental conceptual issue: - Should controls be similar to the cases in all respects other than having the disease in question? - OR, should they be representative of all persons without the disease in the population from which the cases are selected.

Answer 20

School rosters Birth records Selective service lists Insurance company lists Residents of a defined areas (neighborhoods) Random digit dialing - Why is this a problem?

Answer 21

A case is asked to provide the name for a friend who may be more likely to participate in a study - Friends tend to be similar in age and sociodemographic variables - Spouses and siblings May be too similar, including the variables under investigation.

Answer 22

Hospital inpatients are a ‘captive population’ and are clearly identified. Sick people go to hospitals - Many of the risk factors that got them there may also be a risk factor for whatever disease is being studied. - For example, cigarette smoking Selecting from hospitals may mean that controls do not represent the general population. If we use hospital controls, which do we use? - Use a sample of all other admitted patients? Or select patients with a specific ‘other’ diagnosis? - Unlikely to be representative of the reference population. - Perhaps have a lower-than-expected prevalence of the exposure of interest.

Answer 23

Hospital inpatients are a ‘captive population’ and are clearly identified. Sick people go to hospitals - Many of the risk factors that got them there may also be a risk factor for whatever disease is being studied. - For example, cigarette smoking Selecting from hospitals may mean that controls do not represent the general population. If we use hospital controls, which do we use? - Use a sample of all other admitted patients? Or select patients with a specific ‘other’ diagnosis? - Unlikely to be representative of the reference population. - Perhaps have a lower-than-expected prevalence of the exposure of interest.

Answer 24

Major concern is that cases and controls may differ in characteristics or exposures other than the one that has been targeted for study. - Is an observed association due to factors other than the exposure being studied? Confounding One approach is to match the cases and controls so that they are similar to the cases in certain characteristics. Matching may be of two types: - Group matching - Individual matching Match only on variables that we are convinced are risk factors for the disease and are not interested in investigating in this study Matching variables other than these is called overmatching.

Answer 25

Selecting the controls so that they have the proportion of a characteristic identical to that in the case group. Requires that all the cases are selected first, so that proportions can be calculated before selecting controls.

Answer 26

For each individual case selected for the study: - A control is selected who is similar to the case in terms of the specific variable(s) of concern. Often used for hospital controls.

Answer 27

If we want to match cases on too many characteristics, it may be too difficult to find appropriate controls. Gender Age Race Education Income Geography Once we have matched controls to cases according to a given characteristic, we cannot study that characteristic. Why? - Matching creates an artificially identical proportion of a factor in the control group. - Because case-control studies looks at how a much exposure occurs naturally in a population given an outcome: - We cannot look at a factor whose proportion has been artificially established.

Answer 28

Set criteria for exposure - Understand the methods of exposure Collect information: - Observation - Interviews - Questionnaire - Examination of records

Answer 29

Data is collected from subjects by interviews/questionnaires - All humans are limited in their ability to recall information People may also not have the information being requested - For example, circumcision If limitation of recall regarding exposure affects all subjects in a study to the same extent (both cases and controls). - Causes misclassification of exposure: - Cases or controls who were exposed will be classified as unexposed - Leading to an underestimate of the true risk of a disease associated with an exposure More serious than information recall - Social desirability - “Skin in the game” Differential recall of important exposures between cases and controls - Can artificially suggest a relationship between exposure and outcome that is not there or is not as strong

Answer 30

Sometimes the exposure that you are investigating is not dichotomous Ie. You cannot have it or not have it. However, sometimes you have an exposure for which you legitimately cannot have a zero amount of. i.e. Blood pressure, weight, height, blood sugar Dichotomous: Have blood pressure vs. have no blood pressure Can we instead think of the exposure as having multiple levels/categories?

Answer 31

We choose one of the levels/categories to serve as the ‘unexposed status’ We call the group that we consider ‘unexposed’ the ‘reference’ group/category/level We compare this group to those we consider to be ‘exposed’ The other levels/categories serve as ‘exposure status’ Each level is a different ‘exposure’ For many health issues, this would be the expected normal/healthy value: The reference is not the reference because it has the most people in it, though this may often be the case We can also arbitrarily pick a reference category for characteristics that have no ‘normal/healthy’ Gender Race Education SES

Answer 32

Statistical power The probability that a statistical test will say there are no significant differences when there really are none Power is typically gained when you have a ratio of at least 1 case to 4 controls Investigators can determine how many controls will be used per case in a case-control study. Multiple controls are frequently used

Answer 33

For rare diseases, there may be a limit to the number of possible cases. Because the number of cases cannot be increased without extending the length of the study a different option is to increase the number of controls. Either: Controls of the same type Controls of different types

Answer 34

All controls come from the same type of source Registry OR Hospitals OR Clinics Can be multiple registries, multiple hospitals etc.

Answer 35

Suppose we’re concerned that our controls are not representative of the rate of exposure that is expected in the population of non-diseased persons. i.e. the controls may be highly selected subset of non-diseased individuals and may have a different exposure To address this problem, we may choose to use an additional control group Like neighborhood controls

Answer 36

- Can be used to study low-prevalence conditions - Relatively quick and easy to complete - Usually inexpensive - Involve smaller number of subjects - Multiple risk factors can be assessed at one time

Answer 37

- Measurement of exposure may be inaccurate - Representativeness of cases and controls may be unknown - Only provides indirect estimates of risk - Data quality may be a factor (information bias) - The temporal relationship between exposure factor and outcome cannot always be ascertained.

Answer 38

We’ve selected all our cases and controls and we ascertained their exposure. If exposure is dichotomous (exposure has occurred, or not occurred), break down into four groups is possible: A cases who were exposed B controls who were exposed C cases who were not exposed D controls who were not exposed

Answer 39

The proportion of cases who were exposed should be greater than the proportion of the controls who were exposed.

Answer 40

In a case-control study: Do not know the incidence in the exposed population or the incidence in the non-exposed population Because we start with the diseased people (cases) and non-diseased people (controls). Because of this, we cannot say that someone has a risk of developing a disease given an exposure. However, we can calculate another measure called the odds ratio. Under certain conditions, the odds ratio can serve as an estimate of risk.

Answer 41

Compares the odds of exposure in the cases to the odds of exposure in the controls

Answer 42

Calculate them from data from - Cross-sectional studies - Cohort studies - Case-control studies

Answer 43

1. We calculate the odds of exposure in cases # of cases with exposure / # of cases without exposure A/C 2. We then calculate the odds of exposure in the controls # of controls with the exposure / # of controls without the exposure B/D 3. Calculate the odds Odds of exposure in the cases/ odds of exposure in the controls (a/c) / (b/d)

Answer 44

OR = 1 - No difference in the odds of the exposure, given outcome status - Those with the outcome have the same amount of exposure than those without - Those with (insert the case outcome) had the same odds of (insert the exposure) than those without (insert the outcome). - There was no relationship between (insert the outcome) and (insert the exposure). OR > 1 - There are higher odds of exposure, given outcome status - Those with the outcome have more of the exposure than those without - Exposure is a risk factor for the disease - Those with (insert the case outcome) had (insert OR) higher odds of (insert the exposure) than those without (insert the outcome). OR < 1 - There is lower odds of exposure, given outcome status - Those with the outcome have less of the exposure than those without - Exposure is a protective factor for the disease - Subtract OR from 1 to indicate how much less the odds are. - Those with (insert the case condition) had (1 – OR) less/lower odds of (insert the exposure) than those without (insert the case condition).

Answer 45

- Are used to determine whether an exposure is related to a disease - Used to compare the magnitude of different risk factors

Answer 46

- The investigator selects a group of exposed individuals and a group of non-exposed individuals - Cannot have the outcome of interest at the start of the study - Follows them over time to see who in each of the groups develops the disease. - Compares the two groups based on exposure.

Answer 47

Typically involves two groups (exposed and unexposed) but can have multiple exposure groups of varying levels. - i.e. blood pressure categories, types of diets, amount of smoking. - Need to pick a ‘reference’ group to serve as the ‘unexposed’ group. Because we are identifying NEW (incident cases) of the disease we can determine whether a temporal relationship exists between the exposure an disease. - Absolutely necessary for determining causality in a disease.

Answer 48

incidence of disease

Answer 49

We want to look at whether a heart murmur (exposure) is a causal factor in atrial fibrillation (outcome). We find a group of individuals (4500) and determine which of them have a significant heart murmur and which of them do not. We follow them for 30 years. Of those with a heart murmur (exposed), 102 developed atrial fibrillation. Of those without the heart murmur (unexposed), 76 developed atrial fibrillation. What is the incidence of atrial fibrillation among those with heart murmur (exposed)? a/a+b 102/ 900 0.11333 x 10n Incidence of atrial fibrillation in exposed persons is 113.3 per 1000 people What is the incidence of atrial fibrillation among those without the heart murmur (unexposed)? c / c+d 76 / 3,600 0.021111 x 10n Incidence of atrial fibrillation in unexposed persons is 21.1 per 1000 people What is the incidence of atrial fibrillation among the entire population? a+c/ a+b+c+d 178 / 4500 0.039555 x 10n Incidence of atrial fibrillation in entire population is 39.6 per 1000 people

Answer 50

Option 1: We create a study population by selecting groups for inclusion in the study on the basis of whether or not they were exposed. Example: find a group of people with a specific occupational exposure to a chemical we think leads to CVD and equal numbers of people with an occupational exposure that did not use that specific chemical.

Answer 51

Option 2: We can select a defined population before any of its members become exposed or before their exposures are identified. - We select a population on the basis of some factor not related to exposure (such as community of residence) - Take histories of or perform tests on the entire population. - Using the results of the histories or the tests, one can separate the population into exposed and nonexposed groups.

Answer 52

Cohort studies often require a long follow-up period, lasting until enough events (outcomes) have occurred. - Length of follow-up in the second option for study population selection is even greater.

Answer 53

The population often must be followed-up for a long period to determine whether the outcome of interest has developed. The study takes a very long time to complete. Funding from grants typically only lasts between 2-5 years

Answer 54

The population often must be followed-up for a long period to determine whether the outcome of interest has developed. The study takes a very long time to complete. Funding from grants typically only lasts between 2-5 years

Answer 55

Also called ‘concurrent cohort’ or ‘longitudinal study’ Investigator identifies the original population at the beginning of the study. Exposure and non-exposure are ascertained during the study Groups are then followed (concurrently/prospectively) into the future, and incidence is measured. Prospective means the data is collected as it happens

Answer 56

Also called ‘historical cohort’ or ‘nonconcurrent’ study - Cohorts are defined from a previous point in time and are not followed into the future. - Exposure status is determined from information or data that was collected in the past (i.e. past clinical records) - The outcome of interest is determined by the researchers in the present Designs for both prospective cohort study and retrospective or historical cohort study are identical: We are comparing exposed and non-exposed populations. Only difference is ‘calendar time’. Can have a combination: Exposure is ascertained from objective records in the past, and follow-up and measurement of outcome continue into the future. Student records about smoking and alcohol from the past Follow them until they graduate school Which ever study design, the participant cannot have the outcome of interest at the time that exposure status is determined.

Answer 57

There are two main types of cohort studies, prospective and retrospective. Combination of the two The main difference between these types: When researchers are collecting information about exposure/outcome in relationship to the present time period.

Answer 58

Prospective One of the most important and best-known prospective cohort studies is the Framingham Study of cardiovascular disease: - Begun in 1948 - Framingham, MA - 30,000 lived there in 1948 - Planned to follow for 20 years - Residents were eligible if they were 30-62 years of age. Took a sample of 5,127 men and women, who did not have heart disease at the time the study began. Exposures: smoking, obesity, high blood pressure, elevated cholesterol, low levels of physical activity, and others. New coronary events were identified by: Examining the study population every two years Daily surveillance of hospitalizations at the only hospital in Framingham. This study used the second option of selecting a cohort population: A defined population was selected on the basis of location of residence or other factors not related to the exposures in question. The population was then observed over time to determine which individuals developed or already had the ‘exposures’ of interest. Doing so provided an important advantage: Permitted the investigators to study multiple exposures at one time Complex interactions among those exposures by using advanced statistical procedures.

Answer 59

Tested the following hypotheses: Incidence of CHD increases with age It occurs earlier and more frequently in males Persons with hypertension develop CHD at a greater rate than those who are ‘normotensive’ Elevated blood cholesterol is associated with increased risk of CHD Tobacco smoking and habitual use of alcohol are associated with increased risk of CHD Increased physical activity is associated with decrease in development of CHD An increase in body weight predisposes a person to the development of CHD An increased rate of development of CHD occurs in patients with diabetes All of the hypotheses seem like common knowledge, right? They are only common knowledge BECAUSE of the Framingham study The study is the origin of the word risk factor.

Answer 60

- Genetic research - Looking at how social networks affect health and prevention

Answer 61

In 1978, Cowan identified a population of women who had been patients at Johns Hopkins Infertility Clinic from 1945-1965 - All had a late first pregnancy - During infertility evaluation, detailed hormonal profiles were taken. - Patients were divided into exposure groups based on their past medical records (hormonal abnormality vs. normal hormones). - Both groups were followed for subsequent development of breast cancer Results showed that women who had hormonal abnormalities had 5.4 times greater risk of developing premenopausal breast cancer. This study: - Was a cohort because it compared exposed and unexposed persons - And was retrospective because an investigator in 1978 looked at records from 1945-1965 to determine exposure status.

Answer 62

Selection bias in cohort studies Were the people who participated in a cohort study different from those who didn’t? Does this difference also impact the likelihood of being exposed or unexposed?

Answer 63

Selection bias in cohort studies Sometimes study individuals are unwilling to participate in all of the study procedures: - Surveys/Questions - Clinical evaluation This is an issue if those who responded and those who didn’t, are different in meaningful ways that effect exposure or outcome. - Sexual behavior questions and STI outcomes.

Answer 64

Selection bias in cohort studies Participants who at one time were actively participating in the study, but have become ‘lost’ at the time of follow-up. - If those who are lost to follow up differ from those not lost to follow-up - The incidence rates calculated in the exposed and non-exposed group will be difficult to interpret. ex: TOP Project - students move schools or leave state

Answer 65

Quality and extent of information obtained is different for exposed persons than for unexposed person’s. - Particularly likely to occur in retrospective cohort studies, in which information is obtained from past records. Quality of information is an issue….and is understandable to a degree. - However, there should be no difference in information between exposed and unexposed individuals.

Answer 66

If the person who decides whether disease has developed in a subject also knows that the subject was exposed: - If that person is aware of the hypothesis being tested - That person’s judgement as to whether the disease developed may be biased by that knowledge. The problem may be addressed by using different people to make the disease assessment and determine whether this person was exposed. Epidemiologists and statisticians who are analyzing data my have strong preconceptions. - They may unintentionally introduce bias into their analyses and their interpretation of the study findings.

Answer 67

We must have some idea of associations of exposure to disease….so that we know what exposures to track. - Indicated when good evidence suggests an association of a disease with certain exposures. - Perhaps after a case-control studies Because of the long follow-up period, the cohort study is a good approach if we can minimize attrition (loss to follow-up) - Easier to do when the interval between exposure and development of disease is shorter.

Answer 68

Determine whether there is a an excess or reduced risk of a certain disease in association with a certain exposure or characteristic.

Answer 69

Risk is defined as the probability of an event (such as developing a disease) occurring. There are several different measures of risk: - Absolute risk - Relative risk - Attributable risk - Odds ratio

Answer 70

Absolute risk: - The incidence of a disease in a whole population. - The number of people experiencing an event in relation to the population at risk Absolute risk can indicate: - Magnitude of the risk in a group of people with all exposures Absolute Risk - Because it does not take into consideration the different risks of disease in unexposed individuals vs. exposed individuals: we Cannot indicate whether the exposure is associated with an increased risk of disease. However, comparison of risk is fundamental to epidemiology. - We do not all have equal risk - Making prevention ineffective without this knowledge

Answer 71

Absolute risk has important implications in both clinical and public health policy. - Though absolute risk does not stipulate any explicit comparison, an implicit comparison is often made whenever we look at the incidence of disease. However, to address the question of association: - We must use approaches that involve explicit comparisons.

Answer 72

We must determine using data obtained in case-control and cohort studies: - Is there excess risk of the disease in persons who have been exposed to a certain agent? Remember foodborne disease

Answer 73

probability of an event occurring in exposed compared to probability of the event in unexposed

Answer 74

= 1 : There was no relationship between the (insert the exposure) and the (insert the outcome). Those with (insert the exposure) had the same risk of (insert the outcome) as those without (insert the exposure). greater than 1 : Those with (insert the exposure) had (insert RR number) times the risk/increased risk of (insert the outcome) compared to those without (insert the exposure). Less than 1: Those with (insert the exposure) had (1 – RR number) less risk/decreased risk of (insert the outcome) compared to those without (insert the exposure).

Answer 75

measure of the strength of an association establishes causal relationships

Answer 76

to know how much of the disease that occurs, can be attributed to a certain exposure

Answer 77

Incidence not due to exposure there are multiple factors for multiple diseases everyone shares the background risk, regardless of wether or not they have the exposure in question

Answer 78

we should subtract the background risk from the total risk

Answer 79

randomized control trial evaluated both the effectiveness and the side effects of new forms of intervention

Answer 80

randomized control trial evaluated both the effectiveness and the side effects of new forms of intervention

Answer 81

observational 1. cross-sectional 2. case-control 3. cohort experimental 1. RCT

Answer 82

observational 1. cross-sectional 2. case-control 3. cohort experimental 1. RCT

Answer 83

evaluate new drug/tech assess screening program assess intervention program evaluate new ways to deliver health services

Answer 84

1. Ambroise Pare (1510-1590) - unplanned trail with cauterization and topical treatment 2. James Link (1716-1794) - Scottish naval physician - planned clinical trial for scurvy - advanced preventative med and nutrition 3. Austin Bradford Hill (1948) - first published RCT

Answer 85

1. define population 2. Randomize treatment and no treatment 3. follow subjects

Answer 86

1. define population 2. Randomize treatment and no treatment 3. follow subjects

Answer 87

inclusion and exclusion criteria must be extremely specific

Answer 88

should be no element of subjective decision-making on the part of the investigator in deciding who is included or not included in the study. Test of adequacy: If we have spelled out our criteria in writing, and someone not involved in the study walks in off the street and applies our criteria to the same population, will that person select the same subjects whom we would have selected?

Answer 89

- can only match on variables that are measurable

Answer 90

- can only match on variables that are measurable

Answer 91

divide or stratifies the population into groups that differ in important ways select random sample from within each group basis for grouping must be known before sampling to address the issue of randomized groups being weighed inefficiently

Answer 92

Participants receive each treatment in a random order they serve as their own controls used when researchers think it will be difficult to find participants

Answer 93

Participants receive each treatment in a random order they serve as their own controls used when researchers think it will be difficult to find participants

Answer 94

- influence of confounders are reduced because each participant serves as own control -statistically efficient, requiring fewer participants

Answer 95

- influence of confounders are reduced because each participant serves as own control -statistically efficient, requiring fewer participants

Answer 96

- possible order treatment is administered may affect outcome - carry-over effect, combated with wash-out period - cant make a group unlearn a skill to act as a control in later phase

Answer 97

tested aspirin for primary prevention of cardio disease tested beta-carotene for primary prevention of cancer - study pop split into aspirin and placebo - aspirin was later split into B-C and placebo - placebo was later split into B-C and placebo result could be both, only Aspirin, only BC, or neither

All sections for Final Flashcards

(121 cards)