What is a Histogram? What do the Vertical bars and Baseline mean?
A Histogram (History of Data) is a bar graph. Vertical lines depict the data frequency. Baselines depict observed scores on the dependent variable
What is a frequency polygon? What to the vertical lines and baseline depict?
A frequency polygon is a line graph. The vertical line depict score intervals or individual scores. The baseline (horizontal axis) depicts frequencies or percentages.
How does a positive scew differ from the normal curve?
There is a lot of negative or low scores with few people having very high scores. So, a curve with a positive scew has a longer tail on the right side (higher score side).
How does a negative scew differ from a normal curve?
Within the data there are a lot of high scores and fewer lower scores. So, the curve has a tail on the left side (lower score side).
What is Kurtosis?
Kurtosis describes the peakedness of a curve or the rate at which a curce rises.
Name both types of Kurtosis.
Platykurtic and Leptokurtic Curves
What is Platykurtic Curve?
Platykurtic curves have distributions that are flat and rise slowly. They are flat.
What is a Leptokurtic Curve?
A leptokurtic curve is a fast-rising curve. This depicts tests that do not spread out or dicriminiate among the scores.
What is tendency?
Tendency = Data Trends
Name the two types of trends.
Central Tencency and Measures of Dispersion
What are the measures of central tendency?
Meadian, Mean, Mode
What are the measures of dispersion?
Range, Variance, and Standard Deviation
What is mode?
The score that most people got.
What is bimodal?
When a set of data has more than one mode it is termed, bimodal.
What is the median and how do you calculate it?
The median is the middle score. If there is an odd number of data, the median is the middle number. If there is an even number of data, you take the sum of the middle two numbers and divide that by two.
How do you calculate mean?
Add up all of the scores and divide by the number of scores.
Where do the mean median and mode fall in a Symmetrical Distribution?
All measures fall in the very middle of the curve.
Where do the mean, median, and mode fall in a positively skewed distribution?
The mode is at the peak of the curve. The the median and the mean follow to the right of the mode.
From left to right: mode median mean
Where do the mean, median, and mode fall in a negatively skewed distribution?
The mode is at the peak of the distribution and the median and mean follow to the left.
From left to right: mean median mode
What is a measure of variablility?
A measure of variability measures how spred out the scores are. It suggests dispersion. Measures of variability cannot be negative.
What do homogeneous scores mean?
There is little variability in the data.
What does heterogenous scores mean?
There is high variability in the data.
Name the measures of variabilty.
Range, Interquartile Range, Variance, and Standard Deviation
What is range?
The difference between the lowest and the highest data points.
What is interquartile range?
The spread among the middle 50% of the scores.
What is variance? How do you measure it?
Variance is how much the scores deviate from the mean. To find variance, you must first find deviation. Deviation is found by distracting the mean of a set of scores from each raw score. Variation is then the average of the squared deviation scores.
Variance is the sum of (the individual scores minus the mean) squared and divided by the number of data points.
What is standard deviation? How do you calculate it?
Standard deviation is another measure of dispersion, it is useful for describing scores (how much they deviate from the mean), puts scores back in original metric. SD = square root of variance
If scores approximate a normal distribution then how many scores in included in + or - 1 Standard Deviation?
If scores approximate a normal distribution then how many scores are there in + or - 2 Standard Deviations?
What is a normal curve? What can it do descriptively and inferentially?
A normal curve is a unimodal, symmetrical graphic depiction of scores.
Descriptively is can locate position of scores and important for norm-referenced interpretation.
Inferentially it has reliability to derive confidence intervals.
How do you cummarize data on more than one variable?
With Bivariate relations, correlations
What are correlations?
Correlations measure the magnitude and direction of the relation between two variables. Pearson r
Name the scales of measurment.
Nominal, Ordinal, Interval, Ratio
What is the nominal scale of measurement?
Classify, no logical order
What is the ordinal scale of measurement?
Classify and rank or order
What is the interval scale of measurement?
Classify, orders, adds zero (arbitrary), and equal units
What is the ratio scale of measurement?
Classify, order, equal units, true zero point, has a true ratio
What are raw scores?
number correct, completion time, etc.
They lack comparability.
Name types of derived scores.
Age/Grade equivalents, Percentile Ranks, Standard Scores
What are some problems with age and grade scores?
They have differeny meanings (raw score of 5 can mean several different things), lots of misenterpretation, ordinal sclae (can't get standard error of measurement), imply constant rate of growth, imply a flase standard, different meanings across tests.
What are percentiles?
Not the percentage correct. As high or higher than xx% of children on this test (not as well or better),
Why are precentiles not useful in comparing scores?
Percentiles overestimeate differences in the center of a normal curve and underestimate differences on the tails of normal curve.
What are standard scores?
They make use of means and standard deviations. They are derived from z-scores. Best scores for comparing.
What are z-scores? How do you calculate z-scores?
z-scores are the number of standard deviations from the mean. Z-scores are easy to convert.
Z scores = (raw-mean) / Standard Deviation.
What is a normative sample?
Normative samples are a representative sample that match the population, is it comparable.
Name two types of measurement error.
Systematic and Random
What is systematic error?
Like a scale that always measures a person 10 pounds lighter
What is random error?
A person reading the weight of scale wrong.
What is a true score?
Hypothetical entities that would result from error free measurement.
What is reliability? How do you measure reliabilty?
Ratio of true score variance to total test score variance
Consistency, precision, trustworthiness
Reliability = true score variance/total variation in a set of scores
The more error, the less likely a peron's score is the result of true variation and less reliable
Extent to which differences in true scores are reflected in differences in observed scores