critical numbers PT

Question 1

what is a case control study

Answer 1

find people with a disease, look back in time and see if they were exposed to risk factor in question
Retrospective

Question 2

what are the positives of a case control study

Answer 2

works well for investigating rare outcomes
fast + cheap
few ethical considerations

Question 3

what are the negatives of a case control study

Answer 3

cannot prove causation/eliminate cofounders
can be difficult to establish order of events
bias (recall)
can only investigate a single disease

Question 4

what is a cross sectional study

Answer 4

take a sample, see who has the disease right then and there

Question 5

what are the positives of a cross sectional study

Answer 5

fast/cheap
few ethical considerations
generates hypothesis

Question 6

what are the negatives of a cross sectional study

Answer 6

cannot prove causation/eliminate bias
less suitable for rare diseases
difficult to get an understanding of order of events
sample bias

Question 7

what is a cohort study

Answer 7

collect information from a sample, some with exposure, some do not (none with outcome)
follow up over time and see if there is a link between exposure and outcome
prospective

Question 8

what are the positives of a cohort study

Answer 8

few ethical considerations

clarity on event sequence

Question 9

what are the negatives of a cohort study

Answer 9

cannot prove causation/eliminate cofounders
not suitable for rare diseases or when disease takes a long time to develop
time consuming/expensive
difficulty following up
patients can change behaviours in the cohort

Question 10

what is a randomised control trial

Answer 10

multiple groups (arms) , give each different exposures and compare outcomes 
can balance arms by matching, randomising, cross-over, placebos, binding

Question 11

what are the positives of a RCT

Answer 11

gold standard - can prove causation by eliminating cofounders
random - less bias

Question 12

what are the negatives of a RCT

Answer 12

not suitable for rare outcome or when outcome takes a long time to develop
time consuming + expensive
often unethical
issues with follow up/ compliance

Question 13

what is an ecological study

Answer 13

massive sample, by looking at data previously collected to look at prevalence, trends and correlation (populations, not individuals)

Question 14

what are the positives of an ecological study

Answer 14

fast/cheap
very large sample - small SE
easy
good to generate hypothesis

Question 15

what are the negatives of ecological studies

Answer 15

variation/ bias/ inconsistency in data

cannot prove causation

Question 16

what is ecological fallacy

Answer 16

where there is a correlation between predictor and outcome, but this does not mean causation

Question 17

what is the target population

Answer 17

the population the sample represents

Question 18

what is the sample population

Answer 18

the people whom data is collected

Question 19

what is random sampling

Answer 19

random number generator, “draw a name out of a hat”. Usually preferred way of sampling.

Question 20

what is systematic sampling

Answer 20

e.g. count of the list and every “k”th element is taken

Question 21

what is convenience sampling

Answer 21

The first people who approach you are used. Easiest technique but likely the worst.

Question 22

what is cluster sampling

Answer 22

Divide the population into groups, usually geographically
Each group is called a cluster, or block
Clusters are randomly selected, each element in the selected cluster used.

Question 23

what is stratified sampling

Answer 23

Divide the population into groups/strata, based not on geography, but some characteristic, e.g. Males or Females.
A sample is taken from each of these strata using either random, systematic or convenience sampling

Question 24

what is sampling bias

Answer 24

sample is not representative of the target population

Question 25

what is recall bias

Answer 25

people fail to remember specifics innocently

Question 26

what is social-desirability bias

Answer 26

incorrect information is given due to societal pressure

Question 27

what is information bias

Answer 27

where data is consistently measured wrong

Question 28

what is volunteer bias

Answer 28

volunteers aren't representative

Question 29

what is produced bias

Answer 29

subjects in different arms are treated differently

Question 30

what is reliability

Answer 30

how consistent the results of the study are

Question 31

what increases reliability

Answer 31

larger sample size | peer reviewed

Question 32

what is validity

Answer 32

does the test measure what it is supposed to? - have confounders been addressed

Question 33

what are the 2 types of numeric variable

Answer 33

continuous (any value within a range) | discrete (whole numbers)

Question 34

what are the 2 types of categorical variables

Answer 34

ordinal (distinct ordering or hierarchy) | nominal (no distinct ordering)

Question 35

what is risk

Answer 35

number of examined outcomes / total number of possible outcomes

Question 36

what is the absolute risk difference?

Answer 36

difference between 2 risks

Question 37

how do you calculate absolute risk difference (ARD)

Answer 37

work out the 2 individual risks for the subsets you're measuring and then subtract them

Question 38

how do you calculate number needed to treat (NNT) or harm (NNH)

Answer 38

NNT/H = 1/ARD

Question 39

how do you calculate risk ratio/relative risk

Answer 39

divide one risk by another

Question 40

what is odds

Answer 40

the ratio of the probability of the occurrence of the event to the probability of non-occurrence

Question 41

odds equation

Answer 41

odds = probability / (1- probability)

Question 42

how do you calculate odds ratio

Answer 42

divide one odd by the other

Question 43

what is sensitivity

Answer 43

The sensitivity of a test is the proportion of people who test positive among all those who actually have the disease = true positive/ true negative + false negative

Question 44

what is specificity

Answer 44

The specificity of a test is the proportion of people who test negative among all those who actually do not have that disease. = true neg/ true neg+ false pos

Question 45

what is positive predictive value (PPV)

Answer 45

the probability that following a positive test result, that individual will truly have that specific disease. = true pos / true pos + false pos

Question 46

what is negative predictive value (NPV)

Answer 46

the probability that following a negative test result, that individual will truly not have that specific disease. = true neg/true neg+ false neg

Question 47

what is test accuracy

Answer 47

the proportion of true result that were revealed | = TP +TN/ TP +TN + FP +FN

Question 48

what is prevalence

Answer 48

the proportion of people within the community with the disease

Question 49

how do you calculate standard deviation

Answer 49

minus the mean from every data point, square it and sum all values together. Following this, divide by n-1 and then square root the entire result

Question 50

what is standard error

Answer 50

the SD of all the sample means S/ square root of n

Question 51

what does standard error assume

Answer 51

the data is normally distributed and there is a sufficient sample size

Question 52

what is interquartile range , how do you calculate it and what is it useful for

Answer 52

Used in conjunction with the median to describe data. Calculated by subtracting the upper quartile (75%) from the lower quartile (25%) Especially useful to use when the data is not normally distributed (i.e. skewed)

Question 53

what are confidence intervals

Answer 53

give limits in which we are confident (in terms of probability) that the true population parameter lies

Question 54

how do you calculate 95% confidence intervals

Answer 54

mean +/- 1.96 x standard error

Question 55

what is the p-value

Answer 55

the probability of obtaining your results or results more extreme, if the null hypothesis is true

Question 56

when do you reject the null hypothesis

Answer 56

if the p-value is less than 0.05

Question 57

using Pearson's correlation coefficient what does +1, -1, and 0 mean

Answer 57

+1 = perfect positive linear association -1 = perfect negative linear association 0 = no linear relation at all

Question 58

simple linear regression formula

Answer 58

``` y = mx + c y - dependent variable m- gradient x- independent variable c- intercept ```

Question 59

what is multiple linear regression

Answer 59

expansion of simple linear regression to include multiple independent variables

Question 60

what is logistic regression

Answer 60

used when your outcome variable (y) is a binary variable

Question 61

what does PICO stand for

Answer 61

P - patient of population I - intervention or indicator C - comparison or control O - outcome