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AS Psychology > RM - Measures of central tendency and dispersion > Flashcards

RM - Measures of central tendency and dispersion Flashcards

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1
Q

What do descriptive statistics do?

A

Identify general patterns and trends.

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2
Q

What are the 4 levels of measurement?

A

Nominal
Ordinal
Interval
Ratio

NOIR

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3
Q

What is nominal data?

A

Data is in separate categories.

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4
Q

What is ordinal data?

A

Data is ordered in some way. The ‘difference’ between each item is not the same.

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5
Q

What is interval data?

A

Data is measured using units of equal intervals.

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6
Q

What is ratio data?

A

There is a true zero point as in most measures of physical quantities.

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7
Q

What level of measurement is it when data is in separate categories?

A

Nominal

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8
Q

What level of measurement is it when data is ordered in some way and the ‘difference’ between each item is not the same?

A

Ordinal

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9
Q

What level of measurement is it when data is measured using units of equal intervals?

A

Interval

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10
Q

What level of measurement is it when there is a true zero point as in most measures of physical quantities?

A

Ratio

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11
Q

What do measures of central tendency do?

A

Inform us about central (or middle) values for a set of data. They are ways of calculating a typical value for a set of data.

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12
Q

What are the 3 measures of central tendency?

A

Mean
Median
Mode

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13
Q

How is mean calculated?

A

By adding up all the data items and dividing by the number of data items.

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14
Q

What levels of data can the mean be used with?

A

Ratio and interval only.

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15
Q

How is the median calculated?

A

All data items must be arranged in order and then the central value is the median. If there is an even number of data items and therefore two middle values, add the two middle values and divide by two.

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16
Q

What levels of data can the median be used with?

A

Ratio, interval and ordinal data only.

17
Q

How is mode calculated?

A

Nominal - category that has the highest frequency count.

Interval and ordinal - the data item that occurs most frequently.

18
Q

What is it called when a set of data has 2 modes?

A

Bi-modal.

19
Q

What are the 2 measures of dispersion?

A

Range

Standard deviation

20
Q

Why is there an addition of 1 when calculating the range of a set of data?

A

Because the bottom number could represent a value as low as 0.5 lower than the bottom number and the top number could represent a number of up to 0.5 higher than what it is (due to rounding etc).

21
Q

What is the most precise method of expressing dispersion?

A

Standard deviation

22
Q

What is standard deviation a measure of?

A

Dispersion but more precisely, a measure of the average distance between each data item above and below the mean, ignoring plus or minus values.

23
Q

What are the strengths of using the mean?

A

It is the most sensitive measure of central tendency because it takes account of the exact distance between all the values of all the data.

24
Q

What are the limitations of using the mean?

A

Its sensitivity means that it can easily be distorted by one (or a few) extreme values and thus end up being misinterpretive of the data as a whole.

Cannot be used with nominal data.

Doesn’t make sense to use it when you have discrete values such as average number of legs.

Therefore the mean isn’t always representative of the data as a whole and should always be considered alongside the standard deviation.

25
Q

What are the strengths of using the median?

A

Not affected by extreme scores.

Appropriate for ordinal (ranked) data.

Can be easier to calculate than the mean.

Therefore, it can be used to describe a variety of data sets, including skewed data and non-normal distributions.

26
Q

What are the limitations of using the median?

A

Not as ‘sensitive’ as the mean because the exact values are not reflected in the final calculation.

27
Q

What are the strengths of using the mode?

A

Unaffected by extreme values.

Much more useful for discrete data.

The only method that can be used when the data are in categories - nominal data.

28
Q

What are the limitations of using the mode?

A

Not a useful way of describing data when there are several modes.

Tells us nothing about the other values in a distribution.

Therefore, the key is to use the mode only with data sets for which it is appropriate.

29
Q

What are the strengths of using the range?

A

Easy to calculate.

Useful for ordinal data or with highly skewed data or when making a quick calculation.

30
Q

What are the limitations of using the range?

A

Affected by extreme values.

Fails to take account of the distribution of the numbers - for example, it doesn’t indicate whether most numbers are closely grouped around the mean or spread out easily.

31
Q

What are the strengths of using standard deviation?

A

A precise measure of dispersion as takes all the exact values into account.

Not difficult to calculate if you have a calculator.

32
Q

What are the limitations of using standard deviation?

A

May hide some of the characteristics of the data set (e.g. extreme values).

Therefore, best used together with the mean to describe interval or ratio data which is normally distributed.

33
Q

Define mean:

A

The arithmetic average of a data set. Takes the exact values of all the data into account.

34
Q

Define measure of central tendency:

A

A descriptive statistic that provides information about a ‘typical’ value for a set of data.

35
Q

Define measure of dispersion:

A

A descriptive statistic that provides information about how spread out a set of data are.

36
Q

Define median:

A

The middle value of a data set when the items are placed in rank order.

37
Q

Define mode:

A

The most frequently occuring value or item in a data set.

38
Q

Define range:

A

The difference between the highest and lowest item in a data set. Usually one is added as a correction.

39
Q

What does standard deviation do?

A

Shows the amount of variation in a data set. It assess the spread of data around the mean.

AS Psychology (69 decks)

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