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PAS statistics > statistics > Flashcards

statistics Flashcards

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1
Q

What does a case series do?

A

tracks subjects with a known exposure

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2
Q

What does a cross-sectional study do?

A

uses data fro a population at a specific point in time

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3
Q

What does a case-control study do?

A

2 existing groups differing in outcome are identified and compared based off causal attribute

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4
Q

What do cohort studies do?

A

you map a cohort and perform cross-sectional itnervals over time

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5
Q

What is the hierarchy of evidence?

A 
systematic reviews
critically-appraised topics
critically-appraise individual articles
RCTs
Cohort studies
Case-controlled studies
background information / expert opinion
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6
Q

what are confounders?

A

another variable associated with the outcome of interest and independent variable.

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7
Q

What is reverse causality?

A

because we are recruiting from the point of outcome, , the outcome may be affecting the variable

(oesophageal cancer may cause people to drink hot tea)

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8
Q

What do RCTs do?

A

similar people are randomly assigned to 2 (or more) groups to rest an intervention

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9
Q

what do systematic reviews do?

A

go through all the literature to identify every published (and some unpublished ones too) to answer the question we are posing

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10
Q

What are the 2 types of quantitative data?

A

continuous

discrete

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11
Q

What are the types of categorical data?

A

2 categories - binary

>2 categories - nominal / ordinal

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12
Q

What would you use to describe information if there are no outliers?

A

mean

standard deviation

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13
Q

What would you use to describe information if there are outliers?

A

Mean

interquartile range

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14
Q

What would a small SD suggest about a mean?

A

it is more useful

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15
Q

What sort of study design would be used to measure treatment effect?

A

RCT

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16
Q

What sort of study design would be used to measure exposure effect?

A

observational studies

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17
Q

In 10 000 control patients, 1 200 had a subsequent vascular event within 1 month…

What is the probability of a vascular event?

A

1 200 / 10 000 =

0.12

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18
Q

In 10 000 control patients, 1 200 had a subsequent vascular event within 1 month…

What is the percentage of those with a vascular event?

A

12%

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19
Q

In 10 000 control patients, 1 200 had a subsequent vascular event within 1 month…

What is the risk of a vascular event?

A

12 per 100

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20
Q

In 10 000 control patients, 1 200 had a subsequent vascular event within 1 month…

What are the odds of a vascular event happening?

A

1200 / 8800 =

0.14

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21
Q

What is relative risk?

A

probability of event on treatment / probability of event on control

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22
Q

What does a risk ratio of 1 suggest?

A

risk equal in intervention and control arm

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23
Q

What does a risk ratio > 1 suggest?

A

risk of outcome greater in treatment arm

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24
Q

What does a risk ratio < 1 suggest?

A

risk of outcome less in treatment arm

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25
If you were looking at an exposure, what might you use instead of 'treatment' or 'control?
risk in the exposed group | risk in the unexposed group
26
Name 3 ways you might interpret the relative risk
as a percentage increase or decrease in risk as percentage of the risk in the other arm risk in the intervention arm is RR times the risk in the control arm
27
What is the number needed to treat?
The number of patients, who on average need to be treated to prevent one event that would otherwise occur NNT is 1/absolute risk difference
28
How do relative and absolute effects compare?
- relative measures are commonly reported - relative measures can look large where an event is rare - absolute measures are less susceptible to misinterpretation NNT is an effective way to communicate to lay population
29
What are odds?
number with event / number without event
30
What is an odds ratio?
the odds of event on treatment / the odds of event on control
31
how does odds ratio compare to relative risk?
it's a bit less intuitive
32
What is a mean difference?
mean in group 1 - mean in group 2
33
What might you use to measure treatment / exposure effects in continuous outcomes?
mean difference
34
What might you use to measure treatment / exposure effects for a binary outcome?
relative measures (risk ratio / relative risk, odds ratio) absolute measures (risk difference)
35
What is sample variability?
the difference between truth (parameter) of the population and sample (statistic)
36
What is a parameter?
a value referring to the population that we cannot know
37
What is the standard error?
- describes the variability in the means - tells us how accurate the mean of any particular sample is compared to the true population mean the mean of 95% of the samples is within 2 SEs of each other
38
What does a large standard error suggest?
the mean from each sample are likely to differ a lot and so could be an inaccurate representation of true population mean
39
What does standard deviation do?
describes the variability in a sample. essentially, how far, on average, a measurement is from the mean about 95% of the sample have an observation within SDs of the sample mean
40
How does SE suggest how certain we are about estimates?
Small study - large SE - uncertain large study - small SE - more certain
41
Which of SD or SE is usually bigger?
SD
42
What does a confidence interval do?
suggests how accurate our estimate is likely to be expresses a range of values which we are pretty sure the population parameter lies in (centre being the sample mean)
43
What is the size of the confidence interval affected by?
1 - variation within the population 2 - sample size 3 - how confident do we want to be?
44
What conditions might make the confidence interval really wide?
greater variation in population small sample we want to be really accurate
45
What does a '95% confidence interval' suggest?
95% of the time, it would contain the true mean
46
How would you calculate the lower value of a confidence interval?
2 SEs below the mean/exposure effect
47
How would you calculate the upper value of a confidence interval?
2 SEs above the mean/exposure effect
48
What does a 95% CI for a RD above 0 (null value) suggest?
95% certain the risk in the treatment arm is greater than in the control arm
49
What does a 95% CI for a RD below 0 (null value) suggest?
95% certain that the risk in the treatment arm is less that the control arm
50
What does a 95% CI for a RD containing 0 (null value) suggest?
there is not enough evidence to say that the risk is different in the treatment arm compared to the control arm
51
Name the 5 steps required to construct a hypothesis test
``` specify null and alternative hypothesis assume the null hypothesis is true and calculate test statistic convert to a p-value assess the evidence interpret the result ```
52
What does a null hypothesis suggest?
(H0) there is no difference
53
What would an alternative hypothesis suggest?
(H1) there is a difference
54
What is a p value?
the probability that the data could have arisen if the null hypothesis H0 were true
55
What does a high p value tell us?
high chance of seeing the difference we've seen if the null hypothesis were true
56
What does a smaller p value suggest?
greater evidence that the null hypothesis is not true
57
How is statistical significance assessed?
p-value
58
How is clinical importance assessed?
estimates | confidence intervals
59
Is a 95% CI contains the null value, then what is the p value likely to be?
>0.05
60
If a 95% CI does not contain the null value, what is the p value likely to be?
<0.05
61
If a 95% CI ends at the null value, what is the p value likely to be?
0.05
62
What are the 3 categories used when comparing 2 CIs?
significant difference unclear if significantly different if boundaries overlap but means don't not significantly different if means overlap
63
What is a forest plot?
a way of summarising results of a systematic review
64
In a forest plot, what sort of studies are given a larger weight?
larger studies

PAS statistics (1 decks)

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