Midterm Flashcards
Descriptive Statistics
Brief descriptive coefficients that reflect either a sample or a population (e.g. mean)
Inferential Statistics
Techniques used to draw inferences about the population from a sample (e.g. estimation)
Population
Complete collection of all elements of the researcher is interested in (e.g. average age of all first-year students in Canada)
Sample
Subset of members selected from the target population (e.g. all first-year students in Canada)
Cases
The entities from with the data is gathered to make up your sample (e.g. one first-year student in Canada)
Variables
Traits that can change values from case to case (e.g. age)
Discrete variables
Measured in units that cannot be subdivided (e.g. sex)
Continuous variables
Measured in a unit that can be subdivided infinitely (e.g. age)
What are the levels/scales of measurement?
Nominal, ordinal, interval, ratio
What is a nominal level of measurement?
Only named, no quantitative value (e.g. sex)
What is an ordinal level of measurement?
Attributes can be ordered (e.g. 1st, 2nd, 3rd place in a race)
What is an interval level of measurement?
Measuring on a scale that has equal units through its scale (e.g. temperature) - negatives
What is a ratio level of measurement
Ranks categories in terms of differences in magnitude, absolute 0 (e.g. speed) - no negatives
What is proportion and how do you calculate it?
Compares part to the whole, P=f/N
where f is part, N is the whole
What is ratio and how do you calculate it?
A number calculated by dividing the number of cases in one category by the number of cases in another, R=f1/f2
where f1 is the smaller category, f2 is the bigger
What is rate and how do you calculate it?
The number of occurrences of an event/characteristic divided by the number of possible occurrences per unit of time (typically multiplied by a larger number e.g. 1000, 10,000). R=(f1/f2)x the given number
What is percent change and how do you calculate it?
Measures the magnitude of change in a variable from time 1 to time 2 (relative increase/decrease over time)
PC=(f2-f1/f1)x100
What is skewness?
When a distribution has a few very high or very low scores, the mean will be pulled in the direction of the extreme scores.
What does a positive/right skew occur?
When the mean is greater than the median
When does a negative/left skew occur?
When the mean is less than the median
When is there no skew?
When the mean is equal to the median
What are percentiles?
Indicate the relative standing of a person or object within a whole distribution. Split a set of ordered data into hundredths
How do you calculate percentiles?
i=P/100(N+1)
1) rank values from lowest to highest
2) calculate which rank is the percentile using the formula
What is inter-quartile range and how do you calculate it?
A measure of spread or dispersion - the difference between the 75th percentile (Q3) and the 25th percentile (Q1).
IQR=Q3-Q1
- to find Q1, find the “median” of the scores above and below the real median
What is variance and how do you calculate it?
The average squared deviation of values from the mean value
- I can’t put the formula in here, but basically:
1) calculate mean
2) subtract mean from each score then square
3) sum
4) divide sum by (n-1)
What is standard deviation and how do you calculate it?
Represents the average distance of a set of scores from the mean
- I can’t put the formula in here, but basically:
1) calculate mean
2) subtract mean from each score then square
3) sum
4) divide sum by (n-1)
5) take the square root of the quotient
What is the coefficient of variation and how do you calculate it?
The ratio of the standard deviation of a distribution to its arithmetic mean
CV=(SD/sample size)x100
What is kurtosis?
Measures the degree of “peakedness” of a distribution.
What is positive kurtosis?
Observations cluster more at the centre and have longer tails
What is negative kurtosis?
Observations cluster less and have shorter tails
What is leptokurtic?
Distribution with a high peak
What is platykurtic?
Distribution with a low peak
What is mesokurtic?
Normal distribution
What are z-scores?
The position a particular value of x in relation to the mean, measured in SD units.
How do you calculate z-score from a raw score?
z=(value-mean)/SD
What are parameters?
Mathematical characteristics of populations, estimated through statistics
What are statistics?
Mathematical characteristics of samples
