Research methods 21 | Distributions Flashcards
What is a normal distribution?
A symmetrical, bell-shaped curve where most scores cluster around the mean; mean, median, and mode are equal.
What are the key features of a normal distribution?
- Symmetrical (mirrored sides) 2. Mean = median = mode 3. Never touches the x-axis (theoretically infinite tails).
How is IQ an example of normal distribution?
Average IQ = 100; scores symmetrically distributed (e.g., 85 and 115 are equally rare).
What percentage of data falls within ±1 SD in a normal distribution?
68% of scores fall within ±1 standard deviation (SD).
What percentage falls within ±2 SD?
95% of scores fall within ±2 SD (e.g., IQ 130 = top 2.5%).
What is a skewed distribution?
An asymmetrical distribution where scores cluster on one side, creating a “tail.”
What is a positive skew?
Tail points right; most scores are low (e.g., very hard test). Mean > median > mode.
What is a negative skew?
Tail points left; most scores are high (e.g., very easy test). Mode > median > mean.
How do mean, median, and mode differ in skewed distributions?
“Mode = highest peak; Median = middle; Mean is pulled toward the tail by extreme scores.”
What graph displays frequency vs. score values?
A histogram (y-axis = frequency, x-axis = score values).
How is abnormality defined using normal distribution?
Statistically rare traits (e.g., IQ <70 or >130 = ±2 SD from mean).
