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UKMLA Prep > Statistics > Flashcards

Statistics Flashcards

1
Q

What does bias describe in a trial?

A

A situation where one outcome is systematically favoured

Variations in definitions and classifications of bias exist.

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2
Q

What is selection bias?

A

Error in assigning individuals to groups, leading to differences that may influence the outcome

Subtypes include sampling bias and volunteer bias.

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3
Q

What is volunteer bias?

A

When subjects who are at risk are more or less likely to participate in a study

Example: A study on Chlamydia prevalence among students.

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4
Q

What is non-responder bias?

A

When those who do not respond to a survey may differ significantly from those who do

Example: People who did not respond to a dietary habits survey likely have poorer diets.

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5
Q

What is recall bias?

A

Difference in the accuracy of recollections retrieved by study participants

Particularly problematic in case-control studies.

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6
Q

What is publication bias?

A

Failure to publish results from valid studies, often due to negative results

Important in meta-analyses.

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7
Q

What is work-up bias?

A

Occurs when clinicians are reluctant to order gold standard tests unless new tests are positive

Can distort study results, affecting specificity and sensitivity.

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8
Q

What is expectation bias?

A

Observers may subconsciously report data that favours expected outcomes

Only a problem in non-blinded trials.

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9
Q

What is the Hawthorne effect?

A

A group changes its behavior due to the knowledge of being studied

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10
Q

What is late-look bias?

A

Gathering information at an inappropriate time, such as studying a fatal disease years later

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11
Q

What is procedure bias?

A

Occurs when subjects in different groups receive different treatments

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12
Q

What is lead-time bias?

A

Occurs when a new test diagnoses a disease earlier without affecting the outcome

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13
Q

What are the four phases of clinical trials?

A

0, I, II, III, IV

Each phase has specific goals and participant numbers.

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14
Q

What is the goal of Phase I clinical trials?

A

Safety assessment, determining side effects in healthy volunteers

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15
Q

What is the goal of Phase II clinical trials?

A

Assess efficacy with a small number of patients affected by a disease

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16
Q

What is the goal of Phase III clinical trials?

A

Assess effectiveness, typically involving hundreds to thousands of participants

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17
Q

What is the goal of Phase IV clinical trials?

A

Post-marketing surveillance to monitor long-term effectiveness and side effects

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18
Q

What is a confidence interval?

A

A range of values that likely includes the true effect of an intervention

Specified probability called the confidence level.

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19
Q

How is the confidence interval calculated?

A

Lower limit = mean - (1.96 * SEM); Upper limit = mean + (1.96 * SEM)

SEM = SD / square root(n)

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20
Q

What does confounding refer to in statistics?

A

A variable that correlates with other variables, leading to spurious results

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21
Q

What is an example of confounding?

A

Age may confound a study on aspirin and colorectal cancer if groups are not matched

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22
Q

What is correlation?

A

A test for the association between variables

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23
Q

What does the correlation coefficient (r) indicate?

A

The degree of correlation between two variables

r can range from -1 to +1.

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24
Q

What is the difference between correlation and regression?

A

Correlation tests for association; regression predicts values of dependent variables

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25
Q

What is linear regression used for?

A

To predict how much one variable changes when another variable is changed

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26
Q

What are the phases of drug development?

A

Phase 1, Phase 2, Phase 3, Phase 4

Each phase has distinct goals and participant criteria.

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27
Q

What does the GRADE system assess?

A

The quality of evidence in systematic reviews and guidelines

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28
Q

What does a forest plot illustrate?

A

Results from different studies, typically in a meta-analysis

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29
Q

What does a funnel plot demonstrate?

A

The existence of publication bias in meta-analyses

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30
Q

What is a box-and-whisker plot?

A

Graphical representation of sample minimum, lower quartile, median, upper quartile, and sample maximum

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31
Q

What is a histogram?

A

Graphical display of continuous data categorized into a number of categories

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32
Q

What is a scatter plot?

A

Graphical representation using Cartesian coordinates to display relationships between variables

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33
Q

What is a box-and-whisker plot?

A

Graphical representation of the sample minimum, lower quartile, median, upper quartile, and sample maximum.

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34
Q

What is the purpose of a funnel plot?

A

Used to demonstrate the existence of publication bias in meta-analyses.

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35
Q

Define a histogram.

A

A graphical display of continuous data where the values have been categorised into a number of categories.

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36
Q

What does a forest plot provide?

A

A graphical representation of the strength of evidence of the constituent trials in meta-analyses.

37
Q

How is a scatter plot represented?

A

Graphical representation using Cartesian coordinates to display values for two variables for a set of data.

38
Q

What does a Kaplan-Meier survival plot show?

A

A plot of the Kaplan-Meier estimate of the survival function showing decreasing survival with time.

39
Q

What is a hazard ratio?

A

Similar to relative risk but used when risk is not constant over time.

40
Q

What is incidence in epidemiology?

A

The number of new cases per population in a given time period.

41
Q

What is prevalence?

A

The total number of cases per population at a particular point in time.

42
Q

Fill in the blank: The formula for prevalence is _______.

A

incidence * duration of condition.

43
Q

How does intention to treat analysis function?

A

All patients randomly assigned to one of the treatments are analysed together, regardless of whether or not they completed or received that treatment.

44
Q

What is the normal distribution also known as?

A

Gaussian distribution or ‘bell-shaped’ distribution.

45
Q

What percentage of values lie within 2 standard deviations of the mean in a normal distribution?

A

95.4%.

46
Q

Define standard deviation.

A

A measure of how much dispersion exists from the mean.

47
Q

What does NNT stand for?

A

Numbers needed to treat.

48
Q

How is absolute risk reduction calculated?

A

ARR = CER - EER or EER - CER.

49
Q

What is the difference between odds and probability?

A

Odds are a ratio of the number of people who incur a particular outcome to those who do not, while probability is the fraction of times an event is expected to occur.

50
Q

What does power refer to in a study?

A

The probability of rejecting the null hypothesis when it is false.

51
Q

True or False: Publication bias refers to the tendency for only studies with negative results to be published.

A

False.

52
Q

Define relative risk.

A

The ratio of risk in the experimental group to risk in the control group.

53
Q

What is sensitivity in the context of screening tests?

A

TP / (TP + FN), the proportion of patients with the condition who have a positive test result.

54
Q

What does specificity measure?

A

TN / (TN + FP), the proportion of patients without the condition who have a negative test result.

55
Q

What is the formula for positive predictive value?

A

TP / (TP + FP).

56
Q

Fill in the blank: Likelihood ratio for a positive test result is _______.

A

sensitivity / (1 - specificity).

57
Q

What does reliability in statistics imply?

A

Consistency of a measure.

58
Q

What is validity in the context of a test?

A

Whether a test accurately measures what it is supposed to measure.

59
Q

What does the null hypothesis state?

A

That two treatments are equally effective.

60
Q

What is the p value?

A

The probability of obtaining a result by chance as extreme as the one observed, assuming the null hypothesis is true.

61
Q

True or False: A Type I error occurs when the null hypothesis is rejected when it is true.

A

True.

62
Q

What is the probability of making a Type II error called?

A

Beta.

63
Q

Fill in the blank: The power of a study is expressed as _______.

A

1 - beta.

64
Q

What is the null hypothesis accepted when it is false?

A

Failing to spot a difference when one really exists, a false negative

This is referred to as a Type II error.

65
Q

What is the probability of making a Type II error called?

A

Beta

66
Q

What does the power of a study represent?

A

The probability of correctly rejecting the null hypothesis when it is false

This is also the probability of detecting a statistically significant difference.

67
Q

How can the power of a study be increased?

A

By increasing the sample size

68
Q

What is a Type I error also known as?

A

Alpha

69
Q

What is the formula for power in hypothesis testing?

A

Power = 1 - the probability of a Type II error

70
Q

What type of data requires parametric tests?

A

Data that is normally distributed

71
Q

Name two examples of parametric tests.

A
  • Student’s t-test
  • Pearson’s product-moment coefficient
72
Q

What is the Mann-Whitney U test used for?

A

To compare ordinal, interval, or ratio scales of unpaired data

73
Q

What does the Wilcoxon signed-rank test compare?

A

Two sets of observations on a single sample

74
Q

What is the chi-squared test used for?

A

To compare proportions or percentages

75
Q

What do normal (Gaussian) distributions satisfy?

A

Mean = median = mode

76
Q

In a positively skewed distribution, which is greater?

A

Mean > median > mode

77
Q

In a negatively skewed distribution, which is less?

A

Mean < median < mode

78
Q

What are the key features of a randomized controlled trial?

A
  • Participants randomly allocated to intervention or control group
  • May have practical or ethical limitations
79
Q

What is a cohort study?

A

Observational and prospective study following selected groups based on exposure to a particular agent

80
Q

What is the usual outcome measure in a cohort study?

A

Relative risk

81
Q

What is the purpose of a case-control study?

A

To identify past exposure to a possible causal agent for a condition by matching cases with controls

82
Q

What is a cross-sectional survey also known as?

A

Prevalence studies

83
Q

What is the highest level of evidence according to levels of evidence?

A

Ia - evidence from meta-analysis of randomized controlled trials

84
Q

What does Grade A recommendation indicate?

A

Based on evidence from at least one randomized controlled trial

85
Q

What is meta-analysis considered in terms of evidence?

A

The ‘gold standard’

86
Q

What is the primary goal of meta-analysis?

A

To increase power and improve estimates of treatment effect or association

87
Q

What can affect meta-analyses?

A

Publication bias

88
Q

What does variance measure?

A

The spread of scores away from the mean

89
Q

How is variance calculated?

A

Variance = square of standard deviation

UKMLA Prep (46 decks)

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