descriptive statistics Flashcards
(16 cards)
What are descriptive statistics in psychology?
Descriptive statistics are used to summarise, organise, and simplify data. They include measures of central tendency, measures of dispersion, and data presentation methods (e.g., tables, graphs)
What are the three measures of central tendency?
• Mean: Arithmetic average.
• Median: Middle value when data is in order.
• Mode: Most frequently occurring value.
When is the mean the most appropriate measure of central tendency?
When data is interval or ratio level and there are no extreme outliers. It is the most mathematically sensitive measure.
What is a strength and limitation of the mean?
• Strength: Uses all data points — sensitive and representative.
• Limitation: Affected by extreme scores (outliers).
What is a strength and limitation of the median?
• Strength: Not affected by extreme scores — good for skewed data.
• Limitation: Doesn’t consider the exact value of every score — less sensitive.
What is a strength and limitation of the mode?
• Strength: Only measure usable with nominal data.
• Limitation: Not useful with small datasets or if multiple modes exist.
What are the three key measures of dispersion?
• Range: Difference between highest and lowest value.
• Standard deviation: Measures spread of scores around the mean.
• Variance: The average squared deviation from the mean.
What are strengths and weaknesses of the range?
• Strength: Easy to calculate.
• Weakness: Affected by extreme values; doesn’t account for distribution of values between extremes.
What is standard deviation, and why is it important?
It measures how much scores deviate from the mean. A low SD suggests consistency; a high SD indicates greater variability. Examiners value understanding of SD over range.
What are strengths and weaknesses of standard deviation?
• Strength: Takes all values into account — provides precise spread.
• Weakness: More complex to calculate and affected by outliers.
What type of data is needed for calculating the mean and standard deviation?
Interval or ratio level data, as both assume equal intervals between values.
Why do examiners often favour SD over range in longer answers?
Because SD provides a more accurate and detailed picture of data variability, showing how consistent results are around the mean — a key concern in psychological research.
What are tables and how are they used in descriptive statistics?
Tables organise raw data or summary statistics in a clear format.
What graph types are used to display descriptive statistics?
Bar charts: For categorical (discrete) data.
• Histograms: For continuous data.
• Line graphs: To show changes over time.
• Scattergrams: For correlations, not descriptive stats directly but often used alongside.
What are the key exam tips for answering questions on descriptive statistics?
• Link the choice of statistic to the type of data and research aims.
• Comment on suitability, not just definition.
• Interpret meaning in context — especially in extended 4–6 mark questions.
Which measures of central tendency are appropriate for each data type?
• Nominal: Mode
• Ordinal: Median
• Interval/Ratio: Mean (if no extreme scores), otherwise median
