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Stats Flashcards

1
Q

what is cohens Kappa statistic?

A

measure of agreement between raters for categorical measures

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2
Q

there are two different types of agreement dependant on which data types?

A

continous

categorical

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3
Q

equivalent of kappas for continous data?

A

Intraclass correlation (ICC)

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4
Q

is agreement the same as correlation?

A

no

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5
Q

which plot can be used to calculate the means and differences between two techniques?

A

Bland-Altman method

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6
Q

Kappa and weighteed kappa is used for which type of data set?

A

categorical ratings

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7
Q

ICC and bland altman is used for which type of data set?

A

continuous

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8
Q

when are repeated measures seen?

A

measuring same experimental unit on several occasions

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9
Q

give examples of repeated measures?

A

glucose uptake by cells at different time points

cholesterol in RCT of new statin at 3,6 and 12 months

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10
Q

what test is commonly used when analysing repeated measures?

A

t-tests

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11
Q

multiple testing when analysing repeated measureshas what effect on error?

A

increases type I error

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12
Q

how is the inc in type I error with multiple testing accounted for?

A

adjustign p-value

Bonferoni correction

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13
Q

why is bonferoni correction necessary?

A

multiple tests assumes aim of study is to show sig difference at every time point but most studies aim to show overall effect

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14
Q

how would you describe the primary hypothesis when dealing with overall analysis of repeated measures?

A

primary hypothesis os global

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15
Q

what is ANOVA?

A

Analysis of Variance

determines whether there are any statistically significant differences between the means of 3 or more unrelated groups

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16
Q

what is sphericity?

A

refers to teh issue of similarity of variances in the differences between treatments

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17
Q

when sphericity is not met what can be used as an alternative to the correction factors?

A

MANOVA

has less power than repeated measures analysis so generally avoided

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18
Q

what can be used in addition to MANOVA if spherivity is not met?

A

Greenhouse-Geisser

Huynh-Feldt adjustment

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19
Q

what are parametric tests?

A

involve estimating parameters such as the mean and assumes that distribution of sample means are normally ditributed

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20
Q

what is skewness?

A

skewed distributions i.e. postive or negative

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21
Q

if distribution is skewed what can be done to normalise data?

A

use log

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22
Q

what are non-parametric tests?

A

tests for situations where nothign is assumed about the distribution

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23
Q

Non-parametric tests are sometimes called?

A

Distribution free tests

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24
Q

what is a practical difference between parametric and non-parametric methods?

A

NP mehtods use ranks of values rather than actual values

25
Q

what is the median?

A

value above and below which 50% of the data lie

26
Q

in symmetric distributions the median and the mean are the same true/false?

A

true

27
Q

in skewed distributions which is more appropriate the median or the mean?

A

the median

28
Q

what is a T-test?

A

used to test whether the mean of a sample is significantly different from another

relies on sample being drawn from a normally distributed population

29
Q

if a sample is not normal what can be used instead of a t-test?

A

Wilcoxin Signed Rank Test

30
Q

what is the difference between teh Wilcoxin signed rank and the Wilcoxin Rank sum?

A

Signed Rank= paired t-test

Rank Sum= independant t-test

31
Q

give an advantage and a disadvantage of a paired t-test?

A

advantage= uses all detail of available data- most powerful test if data normally distributed

disadvantage= assumes data are a random sample from a population which is norally distributed

32
Q

describe paired and not paired comparisons

A

paired- same sample measured on 2 diff occasions

not-paired- two independant samples

(‘matched’ samples by age/gender are paired)

33
Q

what is another name for the Wilcoxin Rank Sum?

A

Mann-Whitney test

34
Q

when is the Mann whitney test used?

A

used when you want to compare two unrelated or INDEPENDANT groups

35
Q

what assumptions does the Mann Whitney have?

A

distributions have similar shape but need not be normal

can be used for small/large sample sizes

36
Q

what is the spearman rank correlation?

A

tests monotonic relationship between 2 measured variables

lies between -1 to +1

37
Q

a spearman rank correlation close to 0 is strong/weak?

A

weak or no correlation

38
Q

when is Chi-squared testing used?

A

when comparing 2 or more groups of categorical or nominal data (as opposed ot measured data)

39
Q

when comparing 3 or more groups and data is not normal what is used when independant and related samples?

A

independant sample= Kruskal-Wallis

related samples= Friedman

40
Q

what are survival regression models?

A

risk of event (mortality) in next time interval t, conditional to having survued to start of interval t

(expressed in terms of hazard function)

41
Q

what is hazard?

A

hazard rate is an instantaneous rate of events as a function of time

42
Q

which model expresses the relationship between the hazard and a set of variables or covariates?

A

The cox model

43
Q

what is hazard ratio?

A

ratio of hazards (HR) in two groups e.g. men v women

(it is the improvement of one group over the other)

44
Q

what happens to the HR over time?

A

stays constant

45
Q

explain the following hazard ratios: HR= 1, HR= <1, HR= >1

A

HR= 1 do not reject null hypothesis (i.e. no difference)

HR= <1 reduction in hazard relative ot comparator i.e 0.6 is 40% reduction

HR= >1 increase in hazard relative to comparator i.e. 1.7 is 70% increase

46
Q

what is the logrank test?

is it parametric or nonparametric

A

a hy[pothesis test used to compare survival distributions of two samples

47
Q

if a 95% CI for a HR included 1 can you reject the null hypothesis?

A

no

48
Q

how is hazard ratio interpretated for continuous and categorical variables?

A

continous i.e. age- HR represents inc per unit in age

categorical i.e. dukes staging- HR represents inc per category

49
Q

when is multiple regression modelling used?

A

to asses relationship between two variables whilst allowing for another variable

50
Q

what is a cofounder?

A

factor which is related to both the variable of interest and the outcome

51
Q

give two examples of selection criteria used when model has many variables?

A

Alaike’s Information Criterion (AIC)

Schwarts’s Bayesian Information Criterion (BIC)

52
Q

multipe regression models are the most used analytical tool in which type of research?

A

quantitive research

53
Q

define correlation

A

strength of the linear relationshop between two variables

54
Q

what is regression analysis?

A

determines nature of a relationship i.e. is there a relationship between alcohol units drank and liver cirrhosis

55
Q

what is pearsons coefficient of correlation?

A

measures the strength of the linear relationship between one dependant and one independant variable

56
Q

what are the values of pearsons coefficient?

A

r= +1 positive correlation

r= -1 negative correlation

r= 0 no linear relationship

57
Q

define residual

A

a residual is teh difference betwween the predicted value (fitted line) and the actual value or unexplained variation

58
Q

what is a durbin watson test?

A

test for autocorrelation in the residuals from a statistical regression analysis

BMSc (2 decks)

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