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STEPH BPT 2021 > Statistics > Flashcards

Statistics Flashcards

1
Q

Reliable test

A

Consistent result

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2
Q

Valid test

A

Reflective of the true value

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3
Q

The mean

A

Average no

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4
Q

The median

A

Middle no in the data set

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5
Q

The null hypothesis

A

nothing of statistical significance happened

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6
Q

The alternative hypotheisis

A

Something of statistical significance did happen and we can therefore reject the null hypothesis

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7
Q

When to use z statistic

A

Examining a sample taken from a population with a known standard deviation

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8
Q

When to use the t statistic

A

Sample of a population with unknown standard deviation (usual case)

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9
Q

P value

A

The chance of finding the value in the control population

A p value of <0.05 means that there is less than a 5% chance of rejecting the null hypothesis when it is actually true

i.e <5% chance the test statistic is due to chance alone rather than statistically different from the control

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10
Q

Type 1 error

A

Rejecting the null hypothesis when it is true

= False positive

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11
Q

Type 2 error

A

Rejecting the alternative hypothesis when it is true

= False negative

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12
Q

Changes that lead to an increase in power

A

Increase in sample size
Increase in significance level
Increase in the detected difference

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13
Q

A confidence level of 95%

A

investigators are 95% confident that the mean value of the population is between this interval (5% of time it will not!)

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14
Q

When to use mean

A

parametric data

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15
Q

When to use median (middle no)

A

Non-parametric data

eg. ordinal data, binary date

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16
Q

The issue with post hoc analysis

A

Inflation of p value and risk of type 1 error

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17
Q

Relative risk

A

risk of outcome in intervention group/risk of outcome in control

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18
Q

Relative risk reduction

A

1 - RR

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19
Q

Absolute risk reduction

A

Risk of outcome in control minus risk of outcome in the intervention group

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20
Q

NNT

A

Number of people need to undergo the intervention in order to prevent the outcome in one person

NNT = 1 / ARR

21
Q

Cross-sectional study

A

Examines the relationship between diseases (or other health- related characteristics) and other variables of interest as they exist in a defined population at one particular time i.e. exposure and outcomes are both measured at the same time.

22
Q

Case-control study

A

Identifies those with the disease and without the disease and compares how they differ in terms of an explanatory variable

23
Q

Cohort study

A

Follows exposed and unexposed people

24
Q

Reason for testing mortality rate over survival time in screening test

A

Leading bias and length bias

25
Q

Allocation bias

A

Researches allocate which intervention the participant is to receive

26
Q

Channeling bias

A

When a patient’s prognosis influences which group they are allocated to

27
Q

Ascertainment bias

A

Type of sample bias, the study population does not represent true population

28
Q

Interviewer bias

A

A systematic difference in how information is obtained, recorded or interpreted

29
Q

Chronological bias

A

Difference between those recruited earlier in the process and those recruited later

30
Q

Recall bias

A

Paticipants do not remember previous events

31
Q

Attrition bias

A

Participants leave the study

32
Q

Placebo

A

improved performance due to intervention

33
Q

Nocebo

A

Worsened performance due to intervention

34
Q

Hawthorne effect

A

participants report improvement because they know they are on the drug/ or being observed

35
Q

Likelihood ratio of a positive test

A

sensitivity / (1-specificity)

36
Q

likelihood ratio of a negative test

A

(1-sensitivity) / specificity

37
Q

False positive rate = (type I error)

A

1 − specificity

38
Q

False negative rate = (type II error)

A

1 − sensitivity

39
Q

Effect of decreased prevalence

A

increases NPV & decreases PPV

40
Q

Effect of increased prevalence

A

decreased NPV ad increased PPV

41
Q

True positive rate

A

sensitivity

42
Q

True negative rate

A

specificity

43
Q

Focus of phase 1 trials

A

pharmacology

44
Q

Focus of phase 2 trial

A

safety

45
Q

Focus of phase 3 trial

A

efficacy

46
Q

Focus of phase 4 trial

A

long term safety

47
Q

Population attributable factor

A

PAFI = [Pe (RR - 1)] divided by [1 + Pe (RR - 1)].

Pe= % of the population exposed to the risk factor

48
Q

Hazard ration

A

Time from recruitment until event

STEPH BPT 2021 (16 decks)

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