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Year 1 Medicine > Critical numbers > Flashcards

Critical numbers Flashcards

1
Q

What is a sample?

A

A selection from a population which aims to represent the whole population.

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2
Q

What is the bradford hills criteria?

A

Criteria used to support a causal association

  • Plausibility: reasonable pathway to link exposure to outcome
  • Consistency: same results if repeated at different times with different people/geographical location
  • Temporality: exposure precedes outcome
  • Strength: with or without a dose response relationship
  • Specificity: causal factor relates only to outcome in question
  • Change in risk factor: incidence drops if risk factor is removed
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3
Q

Name some types of bias and explain

A

Sampling bias, some people are more likely to be included in your sample than others. (omission, inclusive bias)

Recall bias, people cannot remember information correctly
Social- desirability bias, change answers to more acceptable ones

Information bias, errors in your measurements.

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4
Q

What is a confounding factor?

A

Risk factors other than those being studied that influence the outcome

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5
Q

What are the categories of studies?

A

– Experimental vs. Observational
– Retrospective vs. Prospective
– Individual vs. Population level

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6
Q

What is an experimental research method?

A

One where the researcher has made some kind of intervention eg crossover trial or RCT

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7
Q

What is an observational study?

A

There is no intervention data is just collected about what happens, E.g. case-control, cross-sectional,cohort,ecological studies

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8
Q

What is a retrospective study?

A

One which looks back at what has already happened case-control

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9
Q

What is a prospective study?

A

Collect information then follow up over time Cohort study

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10
Q

What is an individual study?

A

Collect information about individuals all studies except ecological.

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11
Q

What is a popilation study?

A

Talk about a whole population

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12
Q

What is the ecological fallacy

A

making inferences from populations about an individual.

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13
Q

Describe case-control studies

A

Find individuals with the outcome and a similar group without and take a random sample of each and see who had the eposure compared to others.

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14
Q

What are the strengths and weaknesses of case-control studies?

A 
Strengths:
Quick and inexpensive
suitable for rare diseases
multiple exposures can be measured
suitable for measuring outbreaks

Weaknesses:
Only a single disease can be measured
not suitable for rare exposures
need data before the study (retrospective study)
affected by selection bias and confounding variables

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15
Q

Describe a cross-sectional study

A

Investigates what is happening at the current time.

Outcomes and exposures are measured simultaneously

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16
Q

What are the strengths and weaknesses of a cross-sectional study?

A

Strengths:
fast and inexpensive
rapid feedback on current events
multiple outcomes and exposures can be studied

Weaknesses
not suitable for rare diseases
limited potential to establish disease aiteology
affected by selection bias and confounding variables

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17
Q

Describe a cohort study

A

Collect information on a sample and follow- up over time to explore who gets the outcome

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18
Q

What are the strengths and weaknesses of a cohort study?

A

Strengths:
useful for demonstrating casual affects
multiple diseases can be studied
multiple exposures can be studied

Weaknesses:
expensive and time-consuming
not suitable for rare diseases
need to deal with confounding factors

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19
Q

Describe a RCT?

A

Have multitple groups with different exposures compare the outcomes to get a causal relationship.

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20
Q

What are the strengths and weaknesses of an RCT?

A

Strengths:
most convincing evidence for cause and effect
The gold standard for evaluating interventions

weaknesses:
expensive
not always practical for showing long term effects
can be affected by non-compliance
not always ethical
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21
Q

What is a crossover trial?

A

an extension to an RCT. everyone does all the arms of the study. which reduces confounding even more as each person can be compared across the arms. thre can be carry-over effects and more technical analyses

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22
Q

What steps should be taken in an RCT to minimise bias?

A

Blinding, randomisation, placebos, matching

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23
Q

What are the two main groupings for variables?

A

Categoric and numeric

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24
Q

What are the types of categoric variables?

A

Binary, ordinal, nominal

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25
Q

what are the numeric variables?

A

Discrete and continuous

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26
Q

What is the odds?

A

number with the outcome/ number without the outcome

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27
Q

How can you quantify differences?

A

Risk differences, risk ratios, absolute risk, and relative risk.

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28
Q

What is risk difference?

A

the difference between the two risks you have calculated

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29
Q

What is a risk ratio?

A

divide one risk by the other. the top group is the focus group compared to the other one.

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30
Q

How do you interpret a risk ratio?

A

RR> 1 the focus risk is higher
RR=1 the two groups are the same
RR<1 the focus risk is lower than the other
1 is no difference

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31
Q

How can you swap the focus of the risk ratio is?

A

inverse 1 divide by it

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32
Q

What is odds ratio?

A

Odds divided by odds

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33
Q

How do you interpret odds ratio?

A

OR is assessed between 0-1

0= no relationship

1 = high probability of the event happening

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34
Q

Why might you use risk ratio?

A

It puts it in context more

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35
Q

Why do we use Odds ratios?

A

they are useful for some statistical methods

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36
Q

If something is very rare how does OR and RR compare?

A

RRroughly= to OR for rare outcoumes

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37
Q

If something is more prevalent what happens to RR and OR?

A

it makes the OR a poor approximation of the RR

38
Q

What is the median

A

middle value in sequential order

39
Q

What is positive skew?

A

where the peak is to the left

the mean is greater than the median which is greater than the mode

40
Q

What is negative skew?

A

most of the values are to the right,

the mean is less than the median which is less than the mode

41
Q

How to decide which measure of spread to use?

A

if it is symmetric and normally distributed (with the median and mean close together) then use mean and SD
Otherwise use median and IQR as they are less affected by skew

42
Q

What is the use of the normal distribution?

A

The sd can tell you about percentage certainty

43
Q

What are the limits of correlation coeffiecient?

A 
-1 = perfect negative correlation
0 = no linear relationship
\+1 = perfect positive correlation
44
Q

What is standard error?

A

How well your sample representing the population.

45
Q

How can standard error be reduced?

A

Enlarging the sample size the more similar the people are.

46
Q

What is the formula for the standard error of a mean?

A

SD/root(n)

47
Q

What is the difference between standard error and standard deviation?

A

Standard deviation is a descriptive value about the data collected

Standard error is an inferential number about how well our estimate represents the true population value

48
Q

What is the use of confidence interval?

A

It is often used as a comparative value between data sets. can be used for inferential statistics

49
Q

What are confidence intervals?

A

The true value is quite certain to lie between those two points.

50
Q

What are confidence interval calculated from?

A

Standard error and SD values

51
Q

What is the null hypothesis?

A

There is no link between the two variables

52
Q

What is a p value?

A

A p-value measures the probability of obtaining the observed results, assuming that the null hypothesis is true

The probability that the mean could be from the standard deviation.

53
Q

If mean is close to the null what will the p value be?

A

Close to one

54
Q

How should you phrase rejecting the null hypothesis?

A

The evidence suggests to reject the null hypothesis

55
Q

What is the generally accepted significant p value?

A

p=0.05 for statistical significance

56
Q

What is another significance test?

A

One sample t test, two sample t test, chisquare tests, ANOVA test, Pearson correlation coefficient

57
Q

What is regression?

A

Plotting the correlation between variables using y=a+bx

58
Q

What is the effect of using multivariable method?

A

It accounts for the effect of confounding factors

59
Q

How can you appraise the study design?

A

Who is studied? are there missing groups over sampling? is it clear what the aim is

60
Q

What can you appraise the descriptive statistics?

A

Summariesed data appropriately, Normal distribution, SD

61
Q

What can you appraise the inferential statistics?

A

p values CI did they look at normality test

62
Q

A 25-year-old woman presents to a general practitioner reporting
that she is suffering from stress and has recently been having increased
negative thoughts and poor concentration. What type of stress response is
this patient experiencing?

A

Cognitive: Cognitive signs of stress - Negative thoughts; Loss of
concentration)

63
Q

An elderly man presents to his general practitioner reporting that he
is suffering from stress. On examination the GP notices that the patients’
blood pressure is raised and his breathing is shallow. What type of stress
response is this patient likely to be experiencing?

A

Physiological: Physiological signs of stress - shallow breathing;
Raised blood pressure; Increase in acid production in the stomach)

64
Q

A 42-year-old woman has attended her general
practitioner reporting that she is suffering from stress. She says
that she very tearful, has been increasingly irritable with her
partner and has had mood swings. What type of stress response
is this patient experiencing?

A

Emotional: Emotional signs of stress - Mood swings;

Tearful; Irritable; Aggressive; Apathetic

65
Q

Which term would best describe: The total number of UK

adults with a BMI greater than 30 (i.e. obese) at a given time?

A

Prevalence: Proportion of a population with a

disease/condition at a point in time

66
Q

Which term would best describe: The detection of early
disease in order to alter its course, for example cancer screening and
the early identification of heart disease?

A

Secondary prevention: Early detection of disease, followed

by appropriate intervention

67
Q

Which term would best describe: The number of
diagnosed cases of alcohol related liver disease per
100,000 in England during 2009.

A

Incidence: Rate at which new cases occur in a

population in a certain time period

68
Q

Which type of study design below would be best to investigate
the following; to identify patients who have had heart attacks and
compare their diet, smoking habits and exercise activity with people
that are similar to them except that they have not had heart attacks?

A

Case control: Observational study of persons with the
disease of interest and a suitable control group (without disease).
Analysis of events that occurred before onset of disease
(retrospective

69
Q

A new drug has been developed to reduce blood pressure and the
drug manufacturer wants to measure its clinical effectiveness in the very
elderly. A professor in care of the elderly agrees to run a research study. In
order to have enough power he will need to recruit patients from the clinics
of other hospitals as well his own patients. Which type of study design would
be most appropriate?

A

RCT: Investigation involving intentional change in some aspect of
the status of the subjects; randomisation of subjects to intervention and
control conditions)

70
Q

What aspect of the relationship between occupation and

asthma could only be examined through prospective studies?

A

(Causation: The existence of a causal relationship between

variables; the cause must precede the effect

71
Q

If these figures came from an analysis of time to
infection (mean= 2.5, median= 1.2, SD=2, IQR= 0.6 to
2.8); which would you expect to see published in the
article:

A

There is a big difference between mean and
median, so not normally distributed. That leads to median,
and IQR goes with the median

72
Q

In a small randomised trial of a new treatment in type 2
diabetes, the mortality in the treated group was half that in the
control group, but the difference was not significant. We can
conclude that:

A

The treatment shows promise (half the mortality) but

we need a larger size to make sure the difference is not by chance

73
Q

The Odds Ratio (OR) of death for a new treatment
compared to placebo is 0.51 (95% 0.30, 0.83). This
means:

A

There is a 49% reduction in the odds of death for

treatment vs. placebo

74
Q

Which of the following is true about linear regression:
A. The predictor variables can be only numeric
B. The outcome variable is binary (yes/no)
C. Can only explore the joint associations between two variables
D. Can remove background associations to reveal a clearer picture of
the relationship between the main exposure of interest and outcome
E. Cannot produce confidence intervals for the coefficients

A

Can remove background associations to reveal a clearer picture of
the relationship between the main exposure of interest and outcome

75
Q

What is prevalence probability?

A

The probability of having a disease at a given point in time

76
Q

What is incidence probability?

A

The probability of getting a disease during a specified point in time

77
Q

What is the incidence rate?

A

The average rate of change over time

78
Q

What is the hazard rate?

A

Instantaneous rate of change.

79
Q

What is conditional probability?

A

The probability that something will happen given that an event has already happened

80
Q

What are odds?

A

The probability that an event will occur.

Range between 0 and 1

81
Q

What is length time bias?

A

Conditions with a longer duration are more likely to be captured in prevalence.

82
Q

Drug A has a risk of 0.6
Drug B has a risk of 0.2. of causing heart attacks

What is the risk difference
What is the risk Ratio
What is the absolute risk difference
What is the relative risk difference

A

Risk difference = 0.4 (0.6-0.2) and therefore is 40%
Risk Ratio = 3 (3x the risk of drug A than B)

Absolute risk = 0.4 (A-B)
Relative risk difference = (A-B)/B *100 = 200%

83
Q

What information does risk difference provide?

A

An absolute measure of the association of exposure on disease occurrence
Gives a clear sense of public health impact

84
Q

What information does risk ratio give?

A

Gives a relative measure

Gives a clear sense of the strength of the effect

85
Q

What is an association?

A

A statistical link between exposure and disease.

may not reflect a cause and effect relationship

86
Q

What is a Causation?

A

A statistical link where a disease is directly caused by exposure.

87
Q

How can sample variability be measured both within a sample and between a sample?

A

Within a sample - use the SD

Between a sample - Use the SE

88
Q

What do 95% confidence intervals mean?

A

That 95% of the data falls within 2 SDs of the mean and this contains the true mean value.

89
Q

What is an application of regression?

A

Develop a model for risk prediction of a clinical outcome

90
Q

What is the difference between crude and adjusted effects?

A

Crude effects do not take confounding variables into account whereas adjusted does.

91
Q

What form are regression lines written in?

A 
Y= a + bx
Y= Continuous outcome
a = intercept
b = coefficient (slope)
x = explanatory  (predictor value) variable

Year 1 Medicine (25 decks)

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