Flashcards in Frequency distribution Deck (13)
What are summary statistics?
Mean, median, mode
- describe typical performance (avg)
What are frequency distributions?
Describe prevalence of different types of performance
--> frq of single variable: How many people did well
--> Frq of mutually exclusive categories: How many ppl like R, Q or T?
Describe grouped frq distribution
- data collected sorted into a specific interval width = group
- groups do not overlap!!
- bar graph
* a trade off between loss of info + being able to see patterns
Describe cumulative frq distribution
1. Raw data = total in each cell
2. Cumulative frq = each cell total + all precedings cell totals
3. Cumulative frq = cum.frq as % of total
= line graph
Describe relative frq distribution
- useful for comparing groups with different totals
= (cell total/ overall total) x 100
What is the difference between raw frq and relative frq distribution on the graph?
- only the scale of the graph changes, not the pattern of frq
What is the normal distribution?
- Normal curve = mathematical abstraction which conveniently describes many frq distribution of scores in rl
What are the properties of the normal distribution?
- bell-shaped + asymptotic at extremes
- symmetrical around the mean
- mean, median + mode all have the same value
What are skewed distributions?
lack symmetry around the central point
- left lean = positive skew
- right lean = negative skew
How doe skews distort interpretations of mean performance?
- RT often show positive skew
- SAY typical performance = 200-300ms
- BUT mean would be much higher because of the disproportionate effect of long RT (outliers)
How could we deal with outliers distorting means?
- use median instead?
- OR principle treatment of outliers
--> "trimmed mean" = delete top 5% of scores
What does kurtosis mean?
is the measure of all the "tail-heaviness" of all distribution