PUB561 > Module 4 > Flashcards

Module 4 Flashcards

(52 cards)

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1
Q

What do the values have to be between for Pearson’s Correlation coefficient?

A

-1 and +1

values f r close to this indicate a strong linear association

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2
Q

What does a r value close to 0 indicate?

A
  • little linear association between variables
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3
Q

What are the hypothesis for Pearson’s Correlation?

A

H0: p=o (no linear association)
H1: p not equal to 0 (linear association

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4
Q

What p-value shows a significant linear correlation?

A

p<0.05

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5
Q

What are the assumptions of a Pearon’s correlation coefficient?

A
  • linear association
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6
Q

What test is used if there is no linear association between two variables?

A
  • Spearman’s (rank) correlation coefficient

- require association to be monotonic

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7
Q

Define Monotonic?

A
  • always increasing or always decreasing (but doesn’t have to be at the same rate
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8
Q

Does a correlation between 2 variables mean there is a cause and effect relationship?

A
  • no

- there may be an unobserved variable that can this

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9
Q

What does correlation measure?

A
  • magnitude of the association between 2 variables
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10
Q

What does regression measure?

A
  • magnitude of dependence of one variable upon another
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11
Q

What is the idea of linear regression?

A
  • find relationship between the independent (x) and dependent (Y) variable
  • want to determine the straight line that best ‘fits’ the data
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12
Q

Can you have more than one independent variable for regression?

A
  • yes
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13
Q

What is the linear regression model formula?

A

Yi=Bo+B1 Xi + Ei

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14
Q

What are the three main steps in regression analysis?

A
  • estimate equation (find coefficients)
  • assess model (significance and assumptions)
  • use good model to make predictions
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15
Q

In Rcomander what is the Bo and B1?

A
  • Bo is the (intercept) under estimate Std.

- B1 is the value under this

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16
Q

What is b1?

A
  • regession coefficient (slope of line)
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17
Q

What is Bo?

A
  • y-intercept

- the value of Y when X=0

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18
Q

What are the assumptions for regression?

A
  • Y and X are linearly related
  • the values of Y are independent from each other
  • the random part of Y (error) is normally distributed around 0 with constant variance
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19
Q

What is the residual?

A
  • is the difference between what our model predicts at a given value of x and what we observe
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20
Q

What are the assumptions for residual analysis?

A
  • normally distributed
  • mean of zero
  • constant variance (homoscedasticity)
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21
Q

What do you do is the variance is not equal for residual analysis?

Study These Flashcards
A
  • transform data (Ynew=log(Yi)

- use different methods (weighted least squares regression)

22
Q

What are the two types of prediction?

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A
  • interpolation (predict Y value using X values within data range)
  • extrapolation (predict Y values using X value beyond sample data)
23
Q

What is a simple linear regression?

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A
  • one dependent variable and one independent variable
24
Q

What is linear regression?

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A
  • one dependent variable and 2 or more independent variables
25
What is the formula for MLR?
Yi= B0+B1 Xi,1 + B2 X1,2 + ......
26
How do you asses a MLR?
- look at each (y,x) bivariate pair
27
What are rhe main steps in MLR analysis?
1. estimate regression equation 2. asses the model and test hypothesis (ANOVA F test, Model validitity, explanatory power/adjusred R^2, multicollinearity, parsimony) 3. test hypotheses regarding individual Xs 4. if model is 'good', use to predict value of dependent variable
28
Why do we use an adjusted R^2?
- the non-adjusted becomes increasingly biased with increasing number of X's
29
What is an example of a partial regression coefficient hypotheses?
- H0: all partial regression coefficients are zero | - H1: at least one partial regression coefficient is not equal to zero
30
What is parsimony?
- principle of explaining the most variation with the leas number of variables
31
What is information criteria (IC)?
- statistics that consider both parsimony and explanatory power together - AIC (akaike IC) - BIC (bayesian IC)
32
What is the basic formula for IC?
IC = lack of fit (= observed y - predicted Y) + penalty (num of parameters)
33
What is multicollinearity?
- occurs when independent variables are not independent
34
How can you identify mylticollinearity on a correlation matrix?
- a high number compared to others between 2 variables
35
How can you calculate the magnitude of multicollinearity?
- Variance inflation factor (VIF)
36
What does VIF indicate?
- increase in B variance due to presence of other collinear variables in model - VIF< 5 is ok
37
What is confounding?
- variables that changes the effect (slope) of an explanatory variable when it is added to the model
38
What is the minimum sample size?
- minimum number of people needed to decalre clinically important effects that are also statistically significant
39
What is power?
- the probability of declaring an effect statistically significant when it is true - larger sample size increases its power
40
What is the ethical principle?
- Inadequate sample sizes (too large or too small) to answer the posed question leads to wasted resources and, in clinical trials, unethical issues
41
What is alpha level?
``` p-value = probability of type 1 error = significance level p-value = 0.05 ```
42
What is beta level?
power = 1-prob of type 2 error power = 0.8 or 0.9 type 2 error (0.2, or 0.1)
43
What are the 4 types of effect size models for sample size?
- pilot study - scientific literature - expert suggestion - wild guess
44
What are the three variables for sample size?
- expected difference - power - sample size
45
What is the difference between correlation and agreement?
- correlation means a consistent ratio | - agreement means the numbers are the same
46
What is used to measure agreement for continuous data?
Bland-Altman plots
47
What is bias?
- a systematic difference
48
What is used to measure agreement for categorical data?
- cross tabulation | - if perfect agreement the off diagonal would be 0
49
What is sensitivity/positive predicitive value?
- proportion of true positives correctly classified
50
What is specificity/ negative predictive value?
- proportion of true negatives correctly classified
51
What can be used to test a questionares reliability?
- Cronbach's alpha
52
What are the rule of thumb for ranges with cronbach's alpha?
- 0-0.7 = unreliable - 0.7-0.8 = adequate - 0.8-0.95 = good - 0.95-1.0 = too similar
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