Descriptive Statistics - 1

Question 1

Frequency

Answer 1

Number of times one value occurs.

Question 2

Frequency Distribution

Answer 2

Write down all the values in order. Count the frequency with which each value occurs.

Question 3

Bar-charts and Histograms

Answer 3

Bar-charts (with gaps) are similar to histograms but the value labels become individual categories as it is not a continuous variable.

Question 4

What are the measures of central tendency?

Answer 4

1) Mean
2) Median
3) Mode

Question 5

Mean

Answer 5

Total scores and divide by number of scores.

Question 6

Median

Answer 6

Put scores in order; pick the one in the middle. More than one median; add together and divide by two.

Question 7

Mode

Answer 7

The score that happens most frequently. ‘Multimodal’ distribution; more than one mode.

Question 8

What are the measures of dispersion?

Answer 8

1) Range
2) Standard deviation

Question 9

Range

Answer 9

Take away the lowest score from the highest score.

Question 10

Standard deviation

Answer 10

It measures how widely spread the values are around the mean. Unlike the range, it take all the values into account.
- If the data values are close to the mean, the SD is small.
- If the data values are far from the mean, the SD is large.
- If all the values are the same, the SD is zero.

You will not need to work out SD in the exam, only demonstrate what it tells us about the data, eg, more individual differences in condition with higher variance (larger SD).

Question 11

Correlational Analysis

Answer 11

In a correlational study, the variables have to be identified and given a numerical value. The correlational relationship is identified and demonstrated using statistical techniques. The direction and strength of the correlation is measured.

Question 12

Direction

Answer 12

• Positive correlation; as one variable increases, the other one also increases (eg. height and weight).
• Negative correlation; as one variable increases, the other variable decreases (eg. age and memory).

Question 13

Graphs features

Answer 13

When drawing graphs, make sure:
- Detailed title
- Axes clearly labelled
- Appropriate choice of scale
- Correct plotting of points or bars

Question 14

When should mean be used?

Answer 14

Assumes at least interval level of data (parametric).

Question 15

Advantages of mean

Answer 15

Most sensitive measure of central tendency, taking all scores into account.

Question 16

Disadvantages of mean

Answer 16

Can be distorted by extreme scores.

Question 17

When should median be used?

Answer 17

Generally used with ordinal level data.

Question 18

Advantages of median

Answer 18

Unaffected by extreme scores. Better than the mean if extreme scores exist.

Question 19

Disadvantages of median

Answer 19

It only takes into account 1 or 2 scores.

Question 20

When should mode be used?

Answer 20

Used with nominal data.

Question 21

Advantages of mode

Answer 21

Similar to the median, unaffected by extreme scores.

Question 22

Disadvantages of mode

Answer 22

Can be dramatically affected by change in 1 score.

Question 23

When should range be used?

Answer 23

Basic measure of variation when the data is consistent.

Question 24

Advantages of range

Answer 24

Easy to calculate.

Question 25

Disadvantages of range

Answer 25

Easily distorted by extreme scores.

Question 26

When should standard deviation be used?

Answer 26

More sensitive measure of dispersion when data is inconsistent.

Question 27

Advantages of standard deviation

Answer 27

Takes into account all scores.

Question 28

Disadvantages of standard deviation

Answer 28

More difficult to calculate than the range.

Question 29

When should correlation be used?

Answer 29

When variables cannot be manipulated.

Question 30

Advantages of correlation

Answer 30

Can statistically analyse situations that could not be manipulated by the researcher for practical/ethical reasons.

Question 31

Disadvantages of correlation

Answer 31

Does not establish cause and effect.