Participants chosen based on availability to be included
* consecutive sample involves recruiting everyone * volunteers may be recruited by announcing the study and requesting those interested to participate
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quota sample
non-random stratified sampling
* quota established from different strata to match the sample to the population
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purposive sample
researchers purposely select participants based on characteristics desired for the sample
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snowball sample
used for rare or sensitive topics
* after initial group is selected to participate, they are asked to identify others who meet criteria, who are then invited to participate
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simple random sample
all indiv are included in the pool as a random selection occurs
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systematic sample
when there is non ordered list available, every nth indiv is selected
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stratified random sample
to improve representativeness (decrease sampling error), strata are created that relate to the accessible population
* random sample within each strata
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cluster sample
when accessible population is large, it is grouped into cluster
* random selection of cluster is made and then population of the cluster, or a random selection of those within the cluster is sampled
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the flaw in bias is ….
systematic
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misclassificaion bias
participants are not correctly classified as having or not having a quality, based on poor operational definition
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recall bias
participants recall (or do not) historical facts based on wanting to identify a relationship (or not)
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reporting bias
participants in one group systematically underreport/overreport an exposure or outcome
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sampling bias
the sample is no representative of the accessible population for a systematic reason (not by chance)
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allocation bias
in nonrandom samples, when individuals with certain qualities are represented differently in groups
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examples of primary research
* research conducted with patients * observational research * experimental research
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observational research
* describes group of indiv on different variables * may be based on an individual, a single group, or more than one person * some separate descriptive research out as a sep category, while other include it as observational
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experimental research
experimental designs used to compare two or more different conditions/interventions to assess efficacy
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examples of secondary research
* research is conducted on the results of primary research * researchers not working with patients * synthesis research
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synthesis research
combines results of various other studies to provide stronger evidence
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examples of observational study design (4)
* case studies * case report * case series * cross-section studies * case-control studies * cohort
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examples of experimental study design (1)
randomized control trials
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what does pyramid of evidence tell us
1. how common 2. validity
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what type of evidence best in treating patients
systematic review and meta-analysis
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observational studies
* primary study design * used commonly in epidemiology * helpful discover new info * researcher doesnt have large amount of control * doesnt determine cause and effect
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which study mostly used in epidemiology
observation
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case studies (2 types)
\*lowest on evidence pyramid
* case report (indiv) * report of single patient with unique phenomenon * case series (group) * report of a group of patients all with same or similar unique phenomenon
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what is the least valid approach to determining cause because of competing variables and lack of control
case studies
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why are case studies useful
1. understand new and unusual presentations of conditions we already know about 2. identify new treatments for both existing and new conditions 3. discover new conditions that were previously unknown 4. begin to develop hypotheses for testing with other study designs
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case studies objective
describe individuals with disease
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case studies population
all included indiv with same disease
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when is case study used
patient or group is available with no comparable group
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caution with using case study
lack of generalizability
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statistical measures of case study
descriptive statistics
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cross-sectional studies
observational study that measures the association of an exposure to the presence or absence of a disease at a particular point in time
* capture moment in time, nothing historical or future
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surveys are examples of
cross-sectional studies
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objective of cross-sectional studies
describe exposure or disease status of a population at a moment in time
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population of cross sectional studies
study participants must be representative of source population
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when is cross section study used
time or budget limited
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what to be careful of with cross sectional study
sample is not representative of pop
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statistical measure of cross-sectional study
prevalence, linear regression (r)
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case-control study
observational study when we compare
* cases- indiv with the phenomenon of interest, and * controls- indiv without phenomenon of interest * gives retrospective * Investigate previous exposure or risk factors
\*study design is retrospective
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case matching
individual (case) and examine controls and try to match in as many dif ways as possible
Ex: patient is F, native american, 60s, diabetes. what is risk factor smoking and COPD, look for control similar age, ethnicity
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objective of case control studies
comparing exposure histories of people with and people without a disease
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population of case control studies
cases and controls must be similar, aside from disease state
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when is case control study used
disease is uncommon, long induction period, or little is known but a source of cases is available
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what to watch out for with case control studies
recall bias
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statistical measure of case control studies
odds ratio
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cohort studies
* can be prospective or retrospective * observational
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prospective study vs retrospective
begins after exposure /risk/intervention and follows groups forward in time
\ looks for groups with conditions, and then looks even further back to establish a baseline
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difference btw cohort and case control
cohort studies groups people by risk/intervention and look for disease, where case control group by disease and look for previous risk/exposure
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objective of cohort
compare rate of disease overtime in people with or without particular exposure
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population of cohort study
participants must be similar except for exposure status, and not have the disease at the start
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when is cohort study used
exposure is somewhat common and there is group available
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what do you watch out for with cohort study
loss to follow up (prospective) and missing records (retrospective)
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statistical measure of cohort
relative risk ratio
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randomized control trials
experimental designs require an intervention, control, and assignment to group
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two key elements of randomized control trials (RTC)
key elements are randomization and control
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T/F control group is always placebo
F
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randomization
participants assigned to groups by chance- the researchers do not select who will be assigned to what group
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T/F blinding and randomization are the same
F- there can be randomization without blinding, and there can be blinding without randomization
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what allows for cause and effect relationship
randomization
* equal likelihood confounding variables spread across groups
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key concepts in RTC (4)
1. rigorous selection of subjects 2. specific protocol and measurement 3. specific measurements 4. blinding
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objective of RTC study
compare outcomes btw those assigned to an intervention and those assigned to a control
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population of RTC study
similar participants assigned to each group
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when is RTC study used
to assess for cause/effect
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what to watch out for with RTC
non compliance
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statistical measure of RTC
efficacy, risk
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what does CONSORT diagram help determine in RTC study
how patients move through a study
ex: how many pt lost in study?
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systematic review
secondary research
* study question and inclusion/exclusion criteria defined * extracted primary study results are raw data for this primary research * extensive search of literature
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objective of systematic review
synthesize existing knowledge
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population of systematic review
published literature
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when is systematic review used
to compare findings of previously conducted studies on a specific topic
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what to watch out for with systematic review
publication bias
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statistical measure of systematic review
none, but may report measures from included studies
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meta analysis
type of systematic review
uses only studies with quantitative results
summary statistic from each included study is included that is then analyzed with other statistics from primary studies
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objective of meta anlysis
synthesize existing knowledge
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population of meta analysis
published literature
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when is meta analysis used
to compare findings of previously conducted studies on a specific topic using pooled statistics
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what to watch out for with meta analysis
publication bias, studies that cannot be fairly compared
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statistical measures of meta analysis
summary measure
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experimenter effect (internal validity threat)
researcher could treat participants differently if they knew what group the participants were in therefor affecting the participants behavior
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observer bias (internal validity threat)
when the researcher knows the hypothesis and variables of the study and has a biased view because they know what they are looking for
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researcher attribute (internal validity threat)
how the characteristics of the researcher can affect the participants (example how they look, gender)
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hawthorne effect (internal validity threat)
participants responses change because they know they are being observed, similar to the social desirability effect
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testing effect (internal validity threat)
taking a pretest before the experiment can influence the participants views which confounds the experimental results internal validity that the conclusions drawn from experimental results accurately reflect the experiment
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maturation (internal validity threat)
people and their surroundings are continually changing, and such changes can effect the experiment
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experimental mortality (internal validity threat)
people drop out of experiment before it is complete (like if there was a smoking psa experiment, the kids who already smoke might just leave)
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selection bias (internal validity threat)
comparisons between two groups of participants means nothing unless these groups are essentially the same at the beginning of the study (random sampling helps us ensure they will be)
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intersubject bias (internal validity threat)
when participants from the control group and the experimental group have accesses to one another and can share information
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compensatory rivalry
those in the control group may try to compensate for lack of stimulus and work harder that normal
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demoralization
feelings of being denied in the control group may result in them just giving up