Task 2: The characteristic score. Flashcards

1
Q

Statistic is

A

the science of learning from data.

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2
Q

Data can be

A

Numerical and qualitative

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3
Q

Cases are

A

the objects described by a set of data.

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4
Q

A label is a

A

special variable used in some data sets to distinguish the different cases.

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5
Q

A variable is

A

the characteristic of a case.

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6
Q

Variables can be

A

Categorical (places the case into a group)

Quantitative (takes numerical values for which arithmetic operations make sense).

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7
Q

Distribution of a variable tells us

A

what values it takes and how often it takes these values.

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8
Q

Explanatory data analysis

A

Statistical tools and ideas that help us examine data to describe their main features.

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9
Q

Categorial representations of a set of variables are

A

Bar graphs (more flexible) and pie charts (include all categories that make up a whole).

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10
Q

Quantitative representations are made with the help of..

A

Stemplots (work better for small numbers that are greater than 0);
and
Histograms (columns don’t have spaces between them).

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11
Q

Tails of the distribution contain..

A

the extreme values.

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12
Q

The two principles of data examination:

A

1- plot your data

2- look for an overall pattern and any striking deviations.

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13
Q

When examining a distribution, take the further three steps:

A

1- Overall patterns + striking deviations
2- Look at the shape (does it have modes = major peaks)
3- Is it symmetric? (mirror image)
4- Is it skewed? (skewed to the right if the right tail is longer)
5. Outliers.

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14
Q

An outliers is

A

an individual value that falls outside the overall pattern.

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15
Q

We can measure the centre with the help of:

A

The mean x(bar) and the median M.

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16
Q

Characteristics of the mean.

A
  • average value;

- is sensitive to the influence of outliers => NOT a resistant measure of the centre.

17
Q

Characteristics of the median.

A
  • midpoint of a distribution;
  • more resistant than the mean;
  • typical. value.
18
Q

How to find the median?

A
  1. arrange all obs. from the smallest to the largest.
  2. (n+1)/2 = M
    that gives the location, not the actual mean.
19
Q

Methods for measuring spread:

A

1-Quartiles Q1 and Q3;

2- Standard deviation s

20
Q

To calculate Q1 and Q3:

A
  1. Find the M.
  2. Q1 (1/4 of the obs.) = the M of the observations whose position is to the left of the location of the overall M.
  3. Q3 (3/4 of the obs.) = the M of those obs. that are located to the right of the overall M.
21
Q

The five-number summary consists of:

A
Minimum
Q1
M
Q3
Maximum.
22
Q

The interquartile range is used for describing..

A

skewed distributions.

23
Q

IQR =

A

Q3 - Q1

24
Q

The 1.5 x IQR is used for detecting

A

suspected outliers.

25
Q

Variance s2 is the..

A

average of squares of the deviations of the observations from their mean.

26
Q

Standard deviation s is the

A

square root of the variance.

27
Q

The sum of the deviations of the observation from their mean will always be..

A

0

28
Q

When there is no spread s =

A

0

29
Q

We only know s when we know the..

A

Mean.

30
Q

s is not

A

resistant.

31
Q

Linear transformations change…

A

the original variable x into the new variable x new.

32
Q

x new =

A

a + bx

33
Q

The characteristics of linear transformation are:

A
  1. it does not change the shape of a distribution.
  2. it changes the origin if a is not equal to 0.
  3. if b > 0 => changes the size of the unit of measurement.