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Flashcards in Statistics for Public Health Deck (39):
1

Define Odds Ratio

The odds ratio is:

The probability of an event happening divided by the probability of it not happening.

2

State the formula for Odds Ratio

Odds = p / 1 - p

3

What entities can you calculate Odds Ratios for?

Can calculate for:

1 entity eg CD4>250 response to AZT

Many groups eg compare different CD4 count groups to a reference group.

4

Why would you convert a RR to the log scale?

So that the range of possible positive and negative values are equivalent.

5

How do you convert a RR result to a log scale result?

Just take the final RR and use the ln function on the calculator.

6

What’s a narrative difference between relative risk (RR) and odds ratio (OR)?

Relative risk is how frequently (likely) one thing happens compared to another. [Both can happen]

Odds ratio is how likely is one thing to happen *versus* how likely is another. [one versus the other happening]

7

What is the direction of logRR when numerator event is more likely than denominator event? i.e numerator is bigger than denominator.

When numerator is bigger the LEGO tower falls to the right in logRR. ie values will be greater than 0.

When numerator is smaller than denominator the tower leans left, like stable society! ie logRR values are less than 0.

8

What is the formulas for Incidence Rate Ratio?

IRR = number of events / study time

9

When would you use an IRR?

To quantify the TTE differences from 2 samples.

10

How would you compare IRR across 3 or more groups?

Use one as the reference group.

11

What is an advantage of using IRR?

It’s a relative risk measure that enables comparison between groups that have differences in follow-up time.

12

What does Kaplan-Meier summarise?

Cumulative proportion event-free (survival)

13

What’s a synonym for Relative Risk?

Rate Ratio

14

What is the Survival equation in the TTE topic?

N(t) - E(t)
S(t) = ————— - S(pEt)
N(t)

15

Where do you take the median time from for a Kaplan-Meier curve that does not exactly equal 0.5?

From the first time point where Survival drops below 0.5

16

Which groups do RR and RD (ARR) relate to? Personal or population-level?

RD to Population

RR to individual risk

17

Define the ‘sampling distribution’

The sampling distribution is:

The theoretical distribution of all possible values of a sample statistic,

From all possible random samples,

Of the same size from the same population

18

State 3 characteristics of the Central Limit Theorem.

Theoretical sampling distribution of a sample statistics will:
1) be approximately normal
2) contain average of the true population level statistic being estimated
3) have variability that is a function of:
a) variation of population-level values
b) the sample size

19

What is the formula for standard error for continuous data?

It is:

20

What is the SE formula for binary data?

It is:

21

What hypothesis test would you use for comparing two population means comprising unpaired continuous data?

Two-sample t-test

aka

unpaired t-test

22

What are the 3 types of data that can be used in a Hypothesis Test?

Continuous (paired, unpaired)
Binary
Time to event

23

What does the p-value report?

The probability of getting your test result if the null hypothesis is true.

24

What hypothesis test would you use for paired (continuous) data?

Paired t-test

25

What is the mnemonic for the steps involved in hypothesis testing?

SAC.TAR

A sac of tar

26

What is the mnemonic and each of the steps when performing a hypothesis test?

SAC.TAR
S State the competing hypotheses (Ho and Ha)
A Assume Ho is True (ie no difference)
C Compute the d of your test result from the null (0) in SEs (standard errors)
T Translate the d into a p-value
A/R Accept or Reject the null hypothesis Ho

27

What is the mnemonic for accepting the null hypothesis?

PGAA

Tiger Woods played in the PGA, and had to go to AA.

28

What do each of the letters in the hypothesis test p-value result stand for?

PGAA
p-value
Greater than
alpha
Accept Ho

29

What is the mnemonic for rejecting the null hypothesis and what do the letters stand for?

PLAR

Klingons reject that humans and Klingon’s are no different (Ho) “kPLAR Picard!
p-value
Less than
alpha
Reject Ho

30

What hypothesis tests would you use for hypothesis testing proportions (RD, RR, OR) between two populations?

2-sample z-test
Chi-square test
Fisher’s Exact Test

31

What tests is the chi-square equivalent to?

Two-sample z-test

And Fisher’s Exact Test

32

What tests gives the same result as a 2-sample z-test?

Chi-square test

Fisher’s Exact Test

33

When would you use Fisher’s exact test instead of chi-square or 2-sample z-test?

When samples from both populations are small.

34

What goes on the rows (left side) and columns (top) of 2x2 error matrix table, and what goes inside it?

Rows:
Decision: Reject Ho
Decision: Accept Ho

Columns:
u1 = u2
u1 != u2

T1 error (alpha). Power
Correct. T2 error

35

What test could you use for hypothesis test comparison of means between more than 2 populations?

ANOVA

Analysis of Variance

36

What test could you use for hypothesis test comparison of proportions between more than 2 populations?

Chi-square

37

What test is ANOVA an extension of, for more than two populations?

2-sample t-test

38

What test could you use for hypothesis test comparison of TTE between more than 2 populations?

Log-rank test

39

What is a layperson definition of standard deviation?

The average difference between:
Any sample value,
And
The overall sample mean

(So instead of standard deviation you could call it the ‘average’ deviation)