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Psychology as a Science > Frequency distribution > Flashcards

Flashcards in Frequency distribution Deck (13)
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What are summary statistics?

Mean, median, mode
- describe typical performance (avg)


What are frequency distributions?

Describe prevalence of different types of performance
- quantitative
--> frq of single variable: How many people did well
- qualitative
--> 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


What are different kurtosis distributions?

- like normal: Mesokurtic distribution
- Positive/ high kurtosis = leptokurtic distribution = more outliers = BAD
- Negative/ low kurtosis = platykurtic distribution = fewer outliers = thinner tails