Lecture 3 Flashcards
Lecture 3:
What are real limits when working with grouped frequency distribution?
Real limits help account for the rounding error between bins as the real limit is the middle value between 2 bins
Lecture 3:
What are the rules for real limits when working with grouped frequency distribution?
The lower real limit is 0.5… meaning add 5 on the end
The upper real limit uses 0.499 with one more decimal place than the data uses
Lecture 3:
What is a Percentile?
A point/position on a continuous scale of 100 such that a certain fraction of the population of raw scores lies at or below that point
-eg; 75th percentile = a score that is equal to or greater than 3/4 of the scores in the raw data set
Lecture 3:
Why are percentiles useful?
Useful because they use a standard score that is derived from raw data & has a known basis for comparison
- commonly used in clinical & educational settings
Lecture 3:
What are 2 things that standard scores allow us to do?
Allow us to;
1.) evaluate raw scores
2.) compare 2 sets of scores that have different units
Lecture 3:
When discussing common percentile divisions… what are quartiles & deciles?
Quartiles = quarters or groups of 25%
Deciles = 100 divided into blocks of 10 so divided into groups of 10%
Lecture 3:
What are the 3 key steps to calculating percentiles?
1.) Rank data in descending order
2.) count how many cases there are up to & including the target value
3.) divide # of cases by total sample (n) & multiply by 100
Lecture 3:
When calculating a percentile with a tie what do you do?
Since we define percentile as a fraction at or below a given score, we use the highest position when there is a tie as it is considered the “highest achievable value”
Lecture 3:
How do you determine a score if given the percentile?
- 4 steps?
1.) convert percentile to decimal
2.) multiply decimal by number of scores (n)
3.) round to the nearest interger
4.) Count that many scores up from the bottom
- Example; if only the top 25% of class get an A…. Then you must find the score at the 75th percentile
Lecture 3:
When calculating a percentile using the equation… what does “X” represent?
The raw score
Lecture 3:
When calculating a percentile using the equation… what does “L” represent?
The lower real limit of the interval in which the raw score falls
Lecture 3:
When calculating a percentile using the equation… what does “i” represent?
The size of interval (the number of scores counted in a bin)
Lecture 3:
When calculating a percentile using the equation… what does “f” represent?
Frequency of the interval in which the raw score falls
Lecture 3:
When calculating a percentile using the equation… what does “C” represent?
The cumulative frequency of the interval immediately below the one in which X falls
Lecture 3:
When calculating a percentile using the equation… what does “N” represent?
The total number of cases