analysis and distributions Flashcards

1
Q

what is a scatterplot?

A

display relations between two quantative variables

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2
Q

how to know if a relationship is strong or weak

A
  1. strong = points lie close to the line
  2. weak = points are widely scattered
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3
Q

what does it mean when variables are correlated?

A

variables are related

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4
Q

what is the purpose of a correlation analysis? (3)

A

determine

  1. if linear relationship
  2. direction of relationship
  3. strength of relationship
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5
Q

what are correlation coefficients

A

number between 1 and -1

tells us strength and direction of relationship

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6
Q

what does a positive correlation coefficent mean?

A

positive relationship

positive correlation

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7
Q

what does a negative corellation coeeficient mean?

A

negative relationship

negative correlation

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8
Q

what is the difference between linear and non linear relationship?

A

linear = measuring correlations okay

non linear = cant measure correlations

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9
Q

what are the two types of coefficient

A
  1. pearson r
  2. spearman r
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10
Q

what is pearson r coefficient?

A
  1. calculated from raw scores
  2. suitable for interval or ratio data
  3. highly affected by outliers
  4. not suitable for skewed data
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11
Q

what is spearman r coefficient?

A
  1. calculated from ranking raw scores
  2. suitable for ordinal data
  3. marginally affected by outliers
  4. suitable for skewed data
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12
Q

what is a density curve?

A

histogram distribution of scores of ppt

useful when lots of ppt

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13
Q

what do density curves show?

A

the overall pattern of a distribution

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14
Q

density curve + median

A

point that divides area into two equal parts

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15
Q

density curve + quartiles

A

point that divide area under curve into quarters

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16
Q

density curve + mode

A

positions at the peak of the curve

17
Q

density curve + mean

A

balancing point of the curve

18
Q

what does symmetrical density curve mean?

A

mean = median = mode

19
Q

what does skewed density curve mean?

A

mean does NOT = median and mode

20
Q

how is a normal distribution described?

A

by a normal curve

21
Q

what is a normal curve? (5)

A
  1. symmetrical
  2. single peaked
  3. tail meet x axis at infinity
  4. location determined = mean
  5. shape determined = standard devation
22
Q

how to assume if data is normally distributed?

A

statistical tests

23
Q

what to do if data is not normally distributed

A

use a non parametric test

24
Q

what are z scores / standard scores?

A

allow us to compare values from different data sets

25
Q

what is the standard score z of an observation ?

A

deviation of x from mean / standard deviation

26
Q

how to get a standard normal distribution

A

standardising all values of a normal distribution

27
Q

what does a standard normal distribution do?

A

allow us to determine proportions of observations

28
Q

why are parametric & non parametric tests used?

A

test significant differences between data sets

29
Q

what are 2 key things about parametric tests?

A
  1. make assumptions about population parameters
  2. require interval or ratio data
30
Q

what does a violation of test assumptions leads to?

A

erroneous interpretations of the data

31
Q

3 key things about non parametric tests

A
  1. make no assumptions on popular parameters
  2. can use nominal data
  3. not as powerful as parametric tests
32
Q

why is the chi square test for goodness of fit used? (4)

A
  1. used on unrelated data
  2. used to answer q about proportions
  3. used to compare different levels of a variable
  4. compare sample proportions to population proportions
33
Q

what are observed frequencies?

A

number of ppt measured in indivdual catergories

34
Q

what are expected frequencies

A

frequencies predicted by the null hypothesis

35
Q
A