Lecture 3 Flashcards
What are the 2 major classes of statistics?
Descriptive
Inferential
What type of statistics summarize aspects of samples or populations?
Descriptive statistics
What are all members of a group that share a common characteristic of interest?
Population
What is a subset of a population that shares the same characteristic of interest?
Sample
We do research with samples because we don’t have access to what?
Entire populations
What are used to make generalizations (inferences) from samples to populations?
Inferential Statistics
Choosing a good sample affects what?
External validity
What is the ability to generalize findings outside the sample?
External validity
What type of sample adequately represents the population of interest?
Representative sample
What type of sample does not adequately reflect the population?
Biased Sample
What are the 2 major sampling strategies?
Probability
Non-probability
Probability sampling uses what to choose a sample representative of the population to avoid bias?
Random selection
Non-probability sampling doesn’t use random sampling so there is no guarantee of what?
that is represents a larger population
What are the probability sampling methods?
True random sampling
Stratified random sampling
Systematic random sampling
Multi-stage random sampling
In true random sampling every person in the population has?
An equal
Independent chance of being selected
In stratified random sampling we identify subgroups in the population and randomly sample from these groups to get what?
Same proportions in sample as represented in population
What type of sampling randomly selects a starting place to choose participants?
Systematic random sampling
What is used in systematic random sampling?
Systematic rule to select particiapnts
In multi-stage random sampling the final random sample is selected through what?
Series of random selection decisions used to eliminate potential particiapnts
What are the non-probability sampling methods?
Convenience Purposive Quota Systematic (non-random) Stratified (non-random) Multi-stage (non-random)
In convenience sampling the sample is choosen based on what?
Convenient access
In purposive sampling the sample is formed by including what?
Available persons who meet a specific criterion, but not randomly.
In quota sampling individuals of a specified group are added to the sample until when?
Until a pre-specified number is met but not randomly
In systematic (non random) sampling the same is selected how?
Through a systematic, not random process
With stratified (non random) sampling the sample is selected how?
To have a specified ratio for each target group but not randomly
In multi-stage (non-random) sampling, the final sample is selected how?
Through a series of non random selection decisions used to eliminate groups of potential particiapnts
What type of sampling is it when stratified samples are selected from designated age groups at the same point in time so the effect of age can be examined?
Cross-sectional sampling
What type of sampling is it when a single sample of participants is measured repeatedly over time so the effect of age or time can be examined?
Longitudinal Sampling
What type of sampling is it when repeated samples of the same population are measured over time so the effect of time can be examined?
Trend Sampling
What type of sampling is a subset of the population that is repeatedly sampled over times so the effect of time can be examined among the subset?
Cohort sampling
What is a count of the number of times a value occurs?
Frequency
What is the term for a distribution showing the frequency for each value of the variable
Frequency distribution
Frequency distributions usually include what other statistics?
Percent
Valid percent
cumulative percent
What are the shapes of distributions?
Skew
Kurtosis
What are the types of skew?
Symmetrical
Negative
Positive
A symmetrical skew means what?
Normal (mean,median,mode are the same)
A negative skew means what?
Mean is lower than median
A positive skew means what?
mean is higher than median
What does the skew tell you?
How much the distribution deviates from symmetry
What is kurtosis?
Peakedness or flatness of distribution
What is a skewness of 0?
Perfectly symmetrical distribution (normal)
What is a skewness < (less than)2 (not 0)?
Normal enough
What is a skewness > (greater than)2 (not 0)?
Skewed
- positive = positive skew
- negative = negative skew
What is the typical or most commonly occurring observation in the data?
Central Tendency
Central tendency includes?
Mode
Median
Mean
What is the most frequently occurring score in distribution?
Mode
What is the score that divides the distribution in half in the middle?
Median
What is the average?
Mean
The mean gives the most what?
Information from data
What allows you to determine how much the scores are clustered around the center of a distribution or how far out they are dispersed (spread)?
Measures of dispersion
What are the 4 main measures of dispersion?
Range
Semi-interquartile Range
Standard Deviation
Variance
What is a very crude measure of dispersion?
Range (highest score-lowest score)
What is a better but not to meaningful measure of dispersion?
Semi-interquartile range
What is the percentage of score that fall below a value?
Percentile rank
What is the average of the score from the mean?
Standard Deviation
Standard deviation is used with the mean for?
Interval or ratio data
What is the average squared deviation of each score from the mean of the distribution
Variance
What do bodies in box plots display?
Location of quartiles
What does the lines extending out from boxes display?
Distance to the furtherest observations that aren’t outliers
What are displayed in box plots as points beyond the lines?
Outliers
What do z-scores allow us to understand?
Individual scores in a distribution
What type of variable can be converted into a z score?
Any continuous variable
What is a standard normal distribution?
- bell-shaped and symmetrical
- mean, median, mode are equal
- total area under curve is 1.00
What do standardized score represent?
How far a score is from the mean in standard deviation units
The sign of the z score tells you what?
positive = above mean negative = below mean 0 = equal to mean
