critical numbers Flashcards

1
Q

experimental trials

A

researcher intervenes/ changes something

  • randomised control trial
  • cross-over trial
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2
Q

observational trials

A

researcher observes only

  • case control
  • cross-sectional
  • cohort
  • ecological
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3
Q

what uses retrospective data

A

case-control study

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4
Q

case-control trials are subject to which kind of bias

A

recall bias

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5
Q

what uses prospective data (collect data at start follows up over time)

A

cohort study

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6
Q

which does not use individual data

A

ecological

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7
Q

which uses a whole population

A

ecological

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8
Q

what is a case-control study

A

finds individuals with a specific outcome and some without
take random sample of each
look to see who had exposure

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9
Q

what is a cross-sectional study

A

snapshot of time/ whats happening now

who currently has exposure/ outcomes

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10
Q

what is a cohort study

A

collect information on a group of people and follow up over time

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11
Q

what is a randomised control trial

A

multiple groups

expose them to different conditions

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12
Q

what is a crossover trial

A

extension of RTC

everyone gets exposed to all conditions but in different orders

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13
Q

steps to avoid bias in an RTC

A

blinding
randomisation
placebos
matching

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14
Q

ordinal variable

A

2 or more categories with a natural ordering

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15
Q

nominal variable

A

2 or more categories with no natural ordering

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16
Q

discrete variable

A

where there is a distinct number of values e.g. age in years, number of times something happens

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17
Q

how to work out the odds of people who like cake

A

people who like cake/people who dont

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18
Q

for risk ratio a/b, what does a value higher than 1 mean?

A

risk in group a is larger than group b (if the number is 1.34, the risk in group a is 34% higher than the risk in group b)

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19
Q

an odds ratio of 1.9 means what (given odds a/ odds b)

A

90% increase in odds of an outcome for a compared to b

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20
Q

when does the risk ratio roughly equal the odds ratio

A

when the outcome is rare

21
Q

when is the risk ratio much smaller than the odds ratio

A

when the outcome is more prevalent (common)

22
Q

why can using the risk ratio in the media be misleading

A

it doesnt take into account sample size

23
Q

what is the standard deviation

A

a measure of how spread out the values are from the mean

24
Q

if the data is skewed, what should we use for the average

A

median and IQR

25
what should you not use for averages when the data is skewed
mean and standard deviation
26
what do we use to represent the standard deviation
σ
27
what do we use to represent the mean
µ
28
what is varience
σ^2
29
in pearsons correlation coefficiant (denoted r), what is a perfect positive correlation?
+1
30
the 2 values that are 1.96 σ away from the mean on each side represent how much of the data
95%
31
How do you work out standard error?
Standard deviation / root (n)
32
What is Standard error?
How precise the mean estimate is
33
What does CI stand for?
Confidence interval
34
How do you write that "we are 95% confident that the toe mean weight for cats is between 3 and 8kg"
95%. CI: 3kg to 8kg
35
What confidence interval is usually used and what is the exception
Normal is 95% but genetics uses 99%
36
How do you calculate the confidence interval?
Mean- ( 1.96 x SE ) = lower bound | Mean + ( 1.96 x SE ) = upper bound
37
How do you get from a 95% confidence interval to a 99%, confidence interval?
Multiply by the standard error (SE)
38
When can't you use the SE?
When the data is not normally distributed and when n<20
39
As the population size increases, the standard error...
Decreases
40
A small p-value means what about the null hypothesis?
We reject the null hypothesis
41
What does a larger sample size do to the p-value?
Makes it smaller
42
If the null hypothesis is not in the 95% confidence value, the p-value will be...
p <0.05
43
What test is used to compare one mean vs a hypothesised mean?
One-sample t-test
44
What test is used to compare means between 2 groups?
Two-sample t-test (student's t-test)
45
What test is used to compare 2 binary variables?
Chi-squared test
46
What test is used to compare means from 3t groups?
ANOVA test
47
What test is used to compare two numeric variables e.g height vs. weight
Pearson correlation coefficient
48
If the p value is 0.03 and the hypotherised value is 10, the confidence interval can't be outside what?
7-13
49
What is Standard error?
How precise the mean estimate is