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what is a case study

study of a particular situation/individual
used to narrow down a very broad field of research into one more easily researchable topic
testing whether scientific theories and models work in the real world


advantages of case studies

focus on specifics
large amounts of data
help adapt ideas and produce novel hypothesis
challenge theoritcal assumptions


disadvantages of case studies

opinion based research
large amounts of data from multiple sources
hard to replicate
hawthorne effect - people change their behaviour when they know they are being watched
researcher bias
time consuming


what is a case control study

a study that compares individuals who have a disease or outcome of interest with indivudals who do not
looks back retrospectively
determins a relationship
often observational


advantages of case control study

good for studying rare conditions of disease
less time needed
simultaneously look at risk factors
useful as inital studies
less costly


disadvantages of case control studies

retrospective - rely on past data and memory
can be difficult to find a suitable control group
selection bias
limited to examining one outcome


what is a cohort study

one or more samples are followed prospectively and subsequent status evaluations with respect to disease or outcome are conducted to determine which risk factors are associated with it


advantages of cohort studies

subject cohorts can be matched
standarisation of criteria is possible
easier and cheaper than randomaised
multiple exposures and outcomes measured
demonstrate direction of causality


disadvantages of cohort studies

cohorts can be difficult to identify due to confounding variables
no randomisation
outcome of interest could take time to occur
costly and time consuming
participants may move between groups
not good for rare diseases


what is a randomised control study

randomly assigning participants into an experimental group or control group
effect of specific treatment/practice


advantages of randomsied studies

easier to blind
results can be analysed with well known stats
populations of participating individuals are clearly idenified
provide strong epidemiological evidence


disadvantages of randomised studies

time consuming
volenteer bais - popluation may not be representative of the whole
does not reveal causation
inefficient for rare diseases


what are kock postulates

1. the microorgaism must be found in abundance in all orgasims suffering from the disease but should not be found in healthy organisms
2. the microrganism must be isolated from a diseased organism and grown in pure culture
3. the cultureed microorganism should cause disease when introduced into a healthy orgaism
4. the microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original


what is the paradigm shift

a change in the way we view concepts and practices


how does a paradigm shift occur

evidence builds up that contridicts the prevaling theory
the current theory undergoes crisis
a new paradigm is eastblished
scientists work normally again


what is PCR used for

to amplify a section of DNA
to detect specific DNA sequences
alter DNA sequences
clone DNA


what are the 3 stages of PCR



what happens in the denaturing stage

a cocktail containing the template DNA and all other core ingredients is heated to 94-95 degrees
the high temp causes the H bonds between the bases of the two strands to break
the strands seperate, these will act as the templates
temp must be maintained for long enough to ensure strands seperate
usually takes between 15-30 secs


what temp is reached in the denaturing stage

94-95 degrees


what happens in the annealing stage

reaction cooled to 50-60 degrees
primers attached to a specific location on the single strand by way of H bonds
once primer is bound, polymerase enzymes attach and start making the complementary strand
the two seperate strands are complementary and run in opposite directions
this steps usually takes about 10-30 secs


what are primers

a single strand of DNA around 20-30 bases long which are designed to be complementray in sequence to the start of each section to be copied


what happens in the extending stage

heat is increased to 72 degrees to enable Taq DBA polymerase
primers and bases attached
results in brand new strand of DNA and a double stranded molecule of DNA


how long is the extending stage

depends on the lenght of DNA sequence being amplified but normally 1 mintue for 1000 bases


how are the results of PCR seen

visualised using gel electrophoersis
fragments of DNA are pulled through a gel matrix by an electrical current and seperare DNA according to size
forms a band on the gel


what is qPCR used for

to qualify the amount of a specific DNA sequence in a sample
quanify experssion levels of specific mRNA to see how active a gene is


how does qPCR work

use reverse transcriptase to create cDNA from mRNA
run normal PCR
die attached to primers, becomes flourescent when bound in double DNA strand


what is the ct value

value when the PCR curve crosses the threshold


what does a higher ct mean

less mRNA detected


calculation for delta ct

ct gene test - ct endogenous control