Research Methods II Flashcards
(174 cards)
Frequency distribution
Organized tabulation of individuals in each category on the scale of measurement.
f (frequency)
Frequency of a particular score.
Cumulative frequency
Accumulation of individual scores as one moves up the scale. Lowest score, sum of all frequencies, and all scores below it. Highest score should have cumulative frequency equal to total sample size.
Cumulative percentile rank
Accumulation of percent of all scores as one moves up the scale. Start with lowest score divide the cumulative frequency of a particular score by the total sample size.
Mean
Sum of scores divided by number of scores. Average.
Median
Score divides distribution in half. 50th percentile.
Mode
Score in distribution with greatest frequency.
Degrees of Freedom (v or df)
Number of values used to estimate a parameter minus the number of parameters to be estimated.
Why use df in sample SD?
All scores in a set of scores are free to vary, EXCEPT for the last score. Last score is restricted if the mean (or the sum) and the number of scores are known. The correct way to get the UNBIASED estimators of the population is to divide the square deviations by N - 1.
Transformation of the Scale for the SD
- Adding or subtracting a constant to each score in a distribution will not change the standard deviation but will change the mean by the same constant.
- Multiplying or dividing each score by a constant causes the standard deviation and the mean to be multiplied or divided by the same constant.
Symmetrical distribution
Distribution which the left side of the distribution “mirrors” the right side of the distribution.
Skewed distribution
Distribution is skewed if one tail is longer than the other. Long tail in positive direction = positive skew. One tail in negative direction = negative.
Order of Mode, Median, & Mean for Positive skew
Left to right:
- Mode
- Median
- Mean
Order of Mode, Median & Mean for negative skew
Left to right:
- Mean
- Median
- Mode
Kurtosis
“Peakedness” or “flatness” of distribution. How fat or thin a distribution is. Degree of frequency distribution is flat (low kurtosis) or peaked (high kurtosis).
Mesokurtic
Distribution with zero kurtosis. Normal distribution.
Leptokurtic
Distribution with positive kurtosis. Acute peak around the mean, fat tails.
Platykurtic
Distribution with negative kurtosis. Small peak around mean, thin tails.
Bimodal distribution
2 modes.
Rectangular distribution
Mean, median & no mode. No mode because all scores have the same frequency.
Sampling error
The amount of error between statistics calculated from sample to corresponding population parameter.
A sampling distribution
Distribution selected by all possible samples of a specific size from the population.
Distribution of sample means
Collection of sample means for all possible random samples of a particular size (n) that can be obtained from the population.
Central Limit Theorem
For any population with mean µ and standard deviation σ, the distribution of sample means for a sample size of n will approach normal distribution with a mean of µ and a standard deviation of σ/ square root n as n approaches infinity.