Chapter 3 - Key Words Flashcards
Sum of X
The sum of the scores in a sample
Measures of Central Tendency
Mean, median, and mode
They call these the measures of central tendency because they TEND to MEASURE what is happening in the CENTER of the scores.
Mode
The most frequently occurring score and is used to summarize nominal data.
How to calculate the mode
Just count how many times each score appears, whichever score (or scores) appear(s) the most is the mode. It’s okay to have more than one mode.
Unimodal
One mode (one humped distribution)
Bimodal
Two modes (two humped distribution)
Median
The middle score (your book calls it the 50th percentile)
How to calculate the median
Line up all the scores
Then cross out the highest score
Then cross out the lowest score
Then repeat until you have the middle score left
*If you’re using a distribution with an even number of scores, you need to calculate the average of the two middle scores, which will be the median.
Mean
The average score. Like the median, it doesn’t necessarily have to appear in the data.
Σ (Sigma)
the Greek capital letter S, called sigma. Sigma is the “summation sign,” indicating to add together the scores.
Deviaition
Always subtract the mean from the raw score when computing a score’s deviation. (X-X)
What does a measure of central tendency indicate?
It indicates where on a variable most scores tend to be located.
What are the three measures of central tendency?
The mode, median, and mean.
What is the mode, and with what type of data is it most appropriate?
The mode is the most frequently occurring score; it is used with nominal scores.
What is the median, and with what type of data is it most appropriate?
What is the mean, and with what type of data is it most appropriate?
The mean is the average score, the mathematical center of a distribution; it is used with normal distributions of interval or ratio scores.
Why does the mean accurately summarize a normal distribution?
Why does the mean inaccurately summarize a skewed distribution?
What do you know about the shape of the distribution if the median is a considerably lower score than the mean?
The mean is the average score, the mathematical center of a distribution; it is used with normal distributions of interval or ratio scores.
What two pieces of information about the location of a raw score does a deviation score convey?
Why does the sum of the deviations around the mean equal zero?
The mean is the center, so the positive deviations cancel out the negative deviations, producing a total of zero.
Why do we use the mean of a sample to predict anyone’s score in that sample?
You misplaced one of the scores in a sample, but you have the other data below. What score should you guess for the missing score? (b) Why?
On a normal distribution, four participants obtained the following deviation scores:–5, 0, +3, and +1. (a) Which person obtained the lowest raw score? How do you know? (b) Which person’s raw score had the lowest frequency? How do you know? (c) Which person’s raw score had the highest frequency? How do you know? (d) Which person obtained the highest raw score? How do you know?
He is incorrect if the variable is something on which it is undesirable to have a high score (e.g., number of errors on a test). In that case, being below the mean with a negative deviation is better.
Kevin claims a deviation of +5 is always better than a deviation of –5. Why is he correct or incorrect?
He is incorrect if the variable is something on which it is undesirable to have a high score (e.g., number of errors on a test). In that case, being below the mean with a negative deviation is better.
(a) In an experiment, what is the rule for when to make a bar graph? (b) Define these scales. (c) What is the rule for when to make a line graph? (d) Define these scales.
