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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
Q

what should you not use for averages when the data is skewed

A

mean and standard deviation

26
Q

what do we use to represent the standard deviation

A

σ

27
Q

what do we use to represent the mean

A

µ

28
Q

what is varience

A

σ^2

29
Q

in pearsons correlation coefficiant (denoted r), what is a perfect positive correlation?

A

+1

30
Q

the 2 values that are 1.96 σ away from the mean on each side represent how much of the data

A

95%

31
Q

How do you work out standard error?

A

Standard deviation / root (n)

32
Q

What is Standard error?

A

How precise the mean estimate is

33
Q

What does CI stand for?

A

Confidence interval

34
Q

How do you write that “we are 95% confident that the toe mean weight for cats is between 3 and 8kg”

A

95%. CI: 3kg to 8kg

35
Q

What confidence interval is usually used and what is the exception

A

Normal is 95% but genetics uses 99%

36
Q

How do you calculate the confidence interval?

A

Mean- ( 1.96 x SE ) = lower bound

Mean + ( 1.96 x SE ) = upper bound

37
Q

How do you get from a 95% confidence interval to a 99%, confidence interval?

A

Multiply by the standard error (SE)

38
Q

When can’t you use the SE?

A

When the data is not normally distributed and when n<20

39
Q

As the population size increases, the standard error…

A

Decreases

40
Q

A small p-value means what about the null hypothesis?

A

We reject the null hypothesis

41
Q

What does a larger sample size do to the p-value?

A

Makes it smaller

42
Q

If the null hypothesis is not in the 95% confidence value, the p-value will be…

A

p <0.05

43
Q

What test is used to compare one mean vs a hypothesised mean?

A

One-sample t-test

44
Q

What test is used to compare means between 2 groups?

A

Two-sample t-test (student’s t-test)

45
Q

What test is used to compare 2 binary variables?

A

Chi-squared test

46
Q

What test is used to compare means from 3t groups?

A

ANOVA test

47
Q

What test is used to compare two numeric variables e.g height vs. weight

A

Pearson correlation coefficient

48
Q

If the p value is 0.03 and the hypotherised value is 10, the confidence interval can’t be outside what?

A

7-13

49
Q

What is Standard error?

A

How precise the mean estimate is

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