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AKT > Statistics - calculations > Flashcards

Statistics - calculations Flashcards

1
Q

Number needed to treat (NNT)
definition

A

How many patients need to be treated with an intervention to reduce the expected number of outcomes by one

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2
Q

Number needed to treat (NNT)
calculation

A

1/absolute risk reduction (ARR)

Round to the next highest number

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3
Q

Absolute risk reduction definition

A

Is the difference between the event rate in the treatment group (experimental event rate (EER) )and the event rate in the control group (control event rate CER)

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4
Q

Absolute risk reduction calculation

A

Outcome undesirable:
ARR=CER-EER

Outcome desirable:
ARR=EER-CER

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5
Q

Experimental event rate (EER) definition/caluation

A

Number who had particular outcome with the intervention / Total number who had the intervention

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6
Q

Control event rate (CER)

A

Number who had a particular outcome with the control/ Total number who had the control

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7
Q

Variance definition

A

A measure of the spread of scores away from the mean

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8
Q

Variance
calculation

A

Square root stand deviation

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9
Q

Standard deviation calculation

A

Square root of variance

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10
Q

Odds definition

A

A ratio of the number of people who incur a particular outcome to the number of people who do not incur the outcome

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11
Q

Odds definition calculation

A

Total no to benefit from new treatment/those who received treatment but didn’t benefit

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12
Q

Odds ratio definition

A

Defined as the ratio of the odds of a particular outcome with experimental treatment and that of control

Usual reported measure in case-control studies. It approximates to relative risk if the outcome of interest is rare

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13
Q

Odds ratio example

A

Odds of experiment arm outcome/odds of placebo outcome = ratio

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14
Q

Probability definition

A

The fraction of times you’d expect to see an event in many trials – when expressed as a single number probability is always 0 and 1

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15
Q

Incidence definition

A

A measure of the number of new cases

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16
Q

Incidence calculation

A

New cases/total group surveyed x requested volume in population

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17
Q

Prevalence definition

A

A snapshot of existing cases

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18
Q

Point prevalence

A

Point prevalence = no. of cases in a defined population/number of people in a defined population at the same time

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19
Q

Period prevalence

A

Period prevalence = no. of identified cases during a specified period of time/total number of people in that population

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20
Q

95% confidence interval definition

A

a range of values within which the true effect of intervention is likely to lie

IF a repeat sample of 100 observations are taken from the same group 95 of them would be expected to lie in that range

21
Q

95% confidence interval calculation

A

Mean +/- 2 x SE

22
Q

Relative risk

A

is the ratio of risk in the experimental group (experimental event rate, EER) to risk in the control group (control event rate, CER). The term relative risk ratio is sometimes used instead of relative risk.
Usual outcome measure in cohort studies

23
Q

relative risk calculation

A

EER/CER

24
Q

Relative risk reduction (RRR) or relative Risk increase (RRI)

A

Divde the absolute risk change by the control event rate

25
Q

Relative risk reduction (RRR) or relative Risk increase (RRI) calculation

A

RRI = (EER-CER)/CER

26
Q

Power of a study definition

A

Probability of correctly rejecting the null hypothesis (that there is no difference between treatment arm and placebo) when it is false (i.e. not making a type II error)

27
Q

Power of a study
calculation

A

Power = 1 – the probability of a type II error

28
Q

Sensitivity calculation

A

TP/(TP+FN)

29
Q

Sensitivity definition

A

Proportion of patients with the condition who have a positive test result

30
Q

Specificity definition

A

Proportion of patients without the condition who have a negative test results

31
Q

Specificity calculation

A

TN/(TN+FP)

32
Q

Positive predictive value definition

A

The chance that the patient has the condition if the diagnostic test is positive

33
Q

Positive predictive value calculation

A

TP/(TP+FP)

34
Q

Negative predictive value definition

A

The chance that the patient does not have the condition if the diagnostic test is negative

35
Q

Negative predictive value calculation

A

TN/(TN+FN)

36
Q

Likelihood ratio for a positive test result definition

A

How much the odds of the disease increase when a test is positive

37
Q

Likelihood ratio for a positive test result calculation

A

Sensitivity/(1-specificity)

38
Q

Likelihood ratio for a negative test result definition

A

How much the odds of the disease decrease when a test is negative

39
Q

Likelihood ratio for a negative test result calculation

A

(1-sensitivity)/specificity

40
Q

Standard error of the mean
definition

A

The standard error of the mean is a good measure to determine the accuracy of the mean value of a dataset. You divide the standard deviation by the square root of your sample size

41
Q

Standard error of the mean
calculation

A

Standard deviation/square root (number of patients)

42
Q

Standardised mortality ratio
Definition

A

is a tool used to compare mortality within different populations while taking into account the effect of confounding factors such as age and sex.

43
Q

SMR Calculation and result indicates

A

It is the observed deaths divided by the expected deaths (sometimes multiplied by 100).

An SMR of 100 (or 1) indicates that the mortality in the group being studied is the same as the standard population. An SMR of greater than 100 indicates a higher than expected amount of mortality.

44
Q

Incidence

A

is the number of new cases per population in a given time period.
New cases in population over a given time period/total population at risk during that time period 2a

Note: don’t forget that people currently with the disease, or those previously positive for it, are not considered at risk.

45
Q

Prevalence definition

A

is the total number of cases per population at a particular point in time. It can be divided into two types:
point prevalence
period prevalence

46
Q

prevalence calculation

A

incidence * duration of condition

47
Q

Point prevalence calculation

A

number of cases in a defined population / number of people in a defined population at the same time

48
Q

Period prevalence calculation

A

number of cases in a defined population / number of people in a defined population at the same time

AKT (10 decks)

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