MEASURING THE DIFFERENCES BETWEEN PROPORTIONS CONFIDENCE INTERVALS Flashcards

1
Q

Why present Confidence intervals

A

It measures the likely difference between proportions is probably more important

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2
Q

If two groups are independant or unpaired what is required

A

The X2 test (chi squared test)

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3
Q

What are the ways to measure confidence intervals?

A
  1. ABSOLUTE DIFFERENCE
    D=π1-π2,
    R=π1/π2
    OR=(πr/(1-π1))/(π2/(1-π2))
  2. THE RELATIVE RISK
  3. THE RATIO
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4
Q

What is the Null hypothesis

A

D=0, R=1, OR=1 are. all the same

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5
Q

Can you work out the probability from the odds or visa versa

A

Yes the probability and odds of an event are EQUIVALENT ways of QUANTIFYING THE SAME DEGREE OF UNCERTAINTY: IF YOU KNOW ONE THEN YOU CAN FIND THE OTHER
For example:
If an event has probability π, then the same event has odds π(1-π) or π/(1-π)
So..
Probability of π=2/3 then odds is (2/3)/(1-2/3)=2.
Odds (n), the probability will be n/(1+n)

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6
Q

What has the probability have to always been between

A

0 and 1

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7
Q

What does odds have to be

A

Bigger than 0

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8
Q

What is the 95% confidence intervals found as

A

D±1.96 x standard error

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9
Q

What is the 99% confidence intervals found as

A

D± 2.58 x standard error

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10
Q

Is there a connection between any odds ratio greater than one between two groups

A

Yes there is a connection between any odds ratio GREATER THAN ONE and its reciprocal, which is between 0 and 1

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11
Q

Are all the values from 1 up to infinity equivalent to the values BETWEEN 0 AND 1 and does it give the distribution of the Odds ratio (OR) a natural skewness

A

Yes all values from 1 upto infinity are in some ways equivalent to the values between 0 and 1 GIVES DISTRIBUTION of the OR A NATURAL SKEWNESS

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12
Q

How to work out the standard error of logOR

A

It is the SQUARE ROOT OF THE SUM OF THE RECIPROCALS OF THE ENTITIES IN THE 2X2 TABLE UNDERLYING THE RATIO

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13
Q

What is the natural logarithm for OR

A

0.8019

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14
Q

How to find the confidence intervals for the OR

A

Confidence intervals for the odds ratio (OR) is found by TAKING THE NATURAL ANTILOG OF THE VALUES (sometimes written as the EXPOTENTIAL of the values)

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15
Q

Who do you find the mid-point inbetween the confidence intervals

A

You do 1/2 (first interval+ second interval)
This will be larger than the Odds Ratio (OR)

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16
Q

Odds ratio (OR) =1 if….

A

The disease/condition/event is EQUALLY LIKELY to happen in exposed and non-exposed subjects

17
Q

Odds Ratio (OR) IS>1 if….

A

More likely to happen in exposed subjects

18
Q

Odds Ratio (OR) IS<1 or <0 if..

A

Less likely to happen in exposed

19
Q

What does Odds ratio (OR) equaling the difference in proportions or their ratios (RR) signify

A

The condition is rare

20
Q

How can confidence intervals be found

A

By getting Cl first for LOG OR and back transforming

21
Q

What do you need to use for Log OR

A

Natural logs

22
Q

What is logistic regression based on

A

The NATURAL LOG TRANSFORMATION (logit)

23
Q

What does the exponential logistic regression coefficient equal

A

The odds ratio