Exam 3 Flashcards
What are the uses of statistics in research?
- Provide a description of the research sample (descriptive statistics)
- Perform statistical tests of significance on research hypotheses (inferential statistics)
What do descriptive characteristics characterize?
- Shape
- Central tendency (averages)
- Variability
What do descriptive statistics do?
*Provide a description (“picture”) of the dataset
Include
–frequency distributions
–measures of central tendency
–measures of variability
*These statistics illustrate the characteristics of a sample
–allow comparison of the sample to other samples
What does a table of rank ordered scores do?
*Shows how many times each value occurred (frequency)
What is a histogram?
- A bar graph
- -composed of a series of columns
- -each representing a score or class interval
What is a normal distribution? (bell shaped)
- Most scores fall in the middle
- Fewer scores found at the extremes
- Symmetrical
- Mean, median and mode represent the same value
- Important assumption for parametric statistics
What is a skewed distribution?
- asymmetrical
- to the right or left
- distribution of scores above and below the mean are not equivalent
- there are specific statistics appropriate to non-normal distributions
What is a positive skew?
- Skewed to the right (tail points to the right)
- Most scores cluster at low end
- Few at high end
what is a negative skew?
- Skewed to the left (tail points to the left)
- Most scores at the high end
- Few at low end
What is mode?
Score that occurs most frequently
What is median?
Value above which there are as many scores as below
What is the mean?
Sum of scores divided by number of scores
How do you measure variability?
- Range
- Percentiles; quartiles
- Variance
- Standard Deviation
- Coefficient of variation
What is range?
Difference b/w highest and lowest values in the distribution
What is percentile?
Percentage of a distribution that is below a specified value
What is variance?
Measure of variability in a distribution, equal to the square of the standard deviation
What is standard deviation?
Descriptive statistic reflecting the variability or dispersion of scores around the mean
What is coefficient of variation?
Measure of relative variation as a %
—(SD/mean) *100
What is a standardized score?
*Expresses scores in terms of standard deviation units
What is inferential statistics?
- Decision making process
* Estimate population characteristics from data from a sample
What is statistical inference?
- Draw valid conclusions from research data
- –Does the sample represent the population?
- Probability and sampling error
What is probability?
- Likelihood an event will occur given all possible outcomes
- p represents probability e.g. p=0.50 that a coin flip will be heads
- Used in research to make decisions about how well sample data estimates characteristics of a population
- Did differences we see b/w treatment groups occur by chance or are we likely to see these differences in the larger population?
- Estimating what would happen to others based on what we observe in our sample
What is sampling error?
- Estimating population characteristics (parameters) from sample data
- -Assumes that samples are random i.e. individuals randomly drawn from the population
- -And that samples represent the population
- Sampling error: sample values and population values differ
Give an example of sampling error
- *Say there are 1000 000 people over the age of 55 years in the population with population mean age of 67 and SD of 5.2 years
- We randomly select 15 people and find that mean age is 62 yrs and SD is 2.7
- A second sample of 15 people might have age of 73 and SD of 6.4
- -i.e. means and SD will very likely differ with each time we sample
