Week 8 data distribution Flashcards

1
Q

What does a normal distribution look like

A

symmetrical and bell shaped with most scores focused towards the middle

Mean, mode and median are equal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What mathematically defines a normal distribution

A

mean and standard deviation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the range of skew

A

-infinity to +infinity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the general rule for analyzing skewness

A

If the z-score of skewness (skewness/standard error of skewness) is > 1.96, the data is substantially skewed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What determines direction of skew

A

direction of tail

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does the order of central tendency look like on a negatively skewed graph

A

mean, median then mode is greatest

Eg on a test, most students score well but very few low (outliers) reducing the mean

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does the order of central tendency look like on a positively skewed graph

A

mode, median then mean the greatest

Most data points concentrated to lower end.

Eg income levels where most people earn less but some outliers earn a lot more

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Kurtosis

A

altitude or peak of distribution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the range of kurtosis

A

-2 (flat) to +infinity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

3 types of kurtosis

A
  1. Mesokurtic
  2. Platykurtic
  3. Leptokurtic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Mesokurtic

A

Neutral degree

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Platykurtic

A

flat but thick in shoulders

Wide peak

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Leptokurtic

A

peaked, thick in Centre and tails

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the normal curve called in kurtosis

A

Mesokurtic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is general rule for analyzing kurtosis

A

if the z score of kurtosis aka kurtosis/standard error of kurtosis is > 1.96, then the data is significantly different from Mesokurtic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Unimodal

17
Q

Bimodal

18
Q

Multimodel

A

more than 2 peaks

19
Q

What could be a cause of bimodal distributions

A

Ptsp may be not good at study so eg take longer first try but shorter second producing vastly different scores

20
Q

in non-linear transformations…

A

all values for a particular variable are transformed

21
Q

how to non-linear transform positively moderate skewed data

A

take the square root of each value

22
Q

how to non-linear transform positively more substantial skewed data

A

take the logarithm of each value

23
Q

how to non-linear transform positively severe skewed data

A

take the reciprocal transformation for each value

24
Q

what do you do first when you want to non-linear transform negatively skewed data

A

first reflect the score, x-1 to have a positive skew

25
how to non-linear transform negatively moderate skewed data
take the square root of each value
26
how to non-linear transform negatively substantial skewed data
take the logarithm
27
how to non-linear transform negatively severe skewed data
take the reciprocal
28
why do we transform data
bring it to a normal shape change the measure correcting skew for stats test
29
difference between non linear and linear transformations
non linear change the shape of distribution scores linear DONT change the shape of the distribution or have an effect on stats analyses - allows us to express data in different units
30
how can you linear transform data
multiply or divide by a constant add or subtract a constant combination of both
31
what is the mean and SD of a normal distribution
mean = 0 SD = 1
32
what does the value of z tell us
how many standard deviation units a particular score is from the mean
33
what does a positive z score indicate
observation is greater than the mean
34
what does z score magnitude or absolute value tell you
how far a score or observation is from the mean
35
what does z-score allow us to calculate
the probability of obtaining a particular score within the distribution/area under the curve