Descriptive Statistics

Question 1

Nominal Data

Answer 1

• This is simple category data of how often something occurs, e.g. how many cars are red, green or blue
• The mode is the measure of central tendency
• It provides little information as the data is categorised and looks only at frequency

Question 2

Ordinal Data

Answer 2

• This is ranked data and indicates the positions of participants within the group as they are placed in an order e.g. highest score to lowest score
• The median (middle score) is used as a measure of central tendency rather than the mean as this can be affected by extreme scores
• The gap between each ranking is unclear as there is no indication of how much of a gap there is between each participant only the order is given

Question 3

Interval Data

Answer 3

• This is measured by a fixed scale with equal intervals and is always measurable in the same way e.g. height in inches or temperature in degrees Celsius
• The mean is used as it gives a precise measure of central tendency
• The mean can be affected by extreme scores

Question 4

Bar Charts

Answer 4

• Present discrete data which is in categories so the bars must be separate
• Used for nominal data and all measures of central tendency
• Can be used to see if data appear to support the alternate hypotheses

Question 5

Histogram/Line Graph

Answer 5

• Show pattern in a whole data set where data is continuous and shows the distribution of scores
• Used for ordinal or interval data
• Line graphs are similar but have connected dots instead of bars

Question 6

Scatter Diagram

Answer 6

• Display findings of correlational studies
• Shows direction (positive/negative) as well as the strength (strong/weak)
• Also shows anomalous scores

Question 7

Raw Data

Answer 7

• Data that psychologists collect for each participant
• There has been no mathematical analysis to this data
• It is represented in a table form and these data tables allow for an overview and help with identifying anomalies so that the appropriate measure of central tendency can be used

Question 8

Primary Data

Answer 8

• Is gathered directly from the participants

Question 9

Primary Data Evaluation

Answer 9

+ Collected specifically to inform the psychologists’ research
+ Researchers know how the data was gathered and the controls that were used and put in place to ensure validity

• Takes a lot of time to collect

Question 10

Secondary Data

Answer 10

• Has already been collected for other purposes e.g. the NHS

Question 11

Secondary Data Evaluation

Answer 11

+ This is data that would be impossible or too expensive for psychologists to collect
+ Often from a period of time so that trends overtime can be analysed

• May not have been collected in a valid or reliable way and there may be extraneous variables which haven’t been considered

Question 12

Mean

Answer 12

• The common average found by adding up all the scores in the data set and dividing by the total number of scores

Question 13

Mode

Answer 13

• The most frequently occurring score

Question 14

Median

Answer 14

• The central point in a set of scores is found by placing the scores in order and finding the one in the middle. In an even group of data add the two middle scores together and divide by two

Question 15

Measures Of Dispersion

Answer 15

• These give an indication of how spread out the results within a data set are, showing how they vary around the measure of central tendency, whether they are clustered or widely dispersed
• Two data sets of the same size and same average could vary considerably in terms of where the majority of the data points are
• Range and standard deviation are used

Question 16

Range

Answer 16

• The simplest measure of spread, often used with ordinal or interval data, it tells us how similar groups are
• Subtract the smallest value from the largest value and then add 1

Question 17

Range Evaluation

Answer 17

+ Quick and easy to calculate

• Affected by extreme values (outliers)
• Does not take into account all values

Question 18

Standard Deviation

Answer 18

• Tells us the average distance of each score from the mean

1. Work out the overall mean
2. Then for each participant subtract the mean from their score – this gives the difference
3. Square each result – this gives the squared difference
4. Find the mean of the squared differences – this gives the variance
5. Square root the variance to give the standard deviation

Question 19

Standard Deviation Evaluation

Answer 19

+ More precise measure of dispersion

• Much harder to calculate than the range