STATS Ch. 4

what does a measure of central tendancy indicate?

it indicates where on a variable most scores tend to be located

what two aspects of data determine which measure of central tendancy to use?

-shape of the distribution
-scale of measurement employed

mode and what type of data is it used with?

-most frequently occuring score
-nominal data

median and with what type of data is it most appropriate?

-score at the 50th percentile
-ordinal and highly skewed scores

mean

-the mathematical center of the distribution
-average score
-used with symmetrical distributions of interval and ratio data (ex: IQ scores)

which measure of central tendency is best to use with a normal ditstribution and why?

the mean because:
-it uses all the info in all of the scores
-its close to most of the scores in a normal distribution
-most inferential stats procedures use it

why is it inappropriate to use the mean with a skewed distribution?

its not near most of the scores in a skewed distribution

which central tendency is used most often in research and why

the mean because behavioral research usually produces data having apporximently a normal distribution and bc behavioral research usually produces interval and ratio data

what info about the location of the score does a deviation score convey?

how far the score is from the mean

why do u use the mean of the sample to predict any score that might be found in that sample?

the mean is the center of the distribution so in the long run over- and underestimates of any present or future score will cancel out (add up to zero)

what does it mean to say that "the sum of the deviations around the mean equals zero

for the scores above the mean, the total distance they are above the mean equals the total distance that the other scores are below the mean

what is the u symbol and how do u determine that value

-mean of the population
-estimate it from the mean of a random sample taken from the population

positive skew

mode, median, mean

negative skew

mean, median, mode

is a deviation score of +5 always better than -5 in general?

she is correct unless the variable is something on which it is undesirable to have a high score. Then being below the mean with a negative deviation is better

which of the following types of scores would a deviation of +5 be better

number of correct answers on a test and time between failure