Lecture 3 Flashcards by Heather Elahi

What are the 2 major classes of statistics?

Descriptive

Inferential

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What type of statistics summarize aspects of samples or populations?

Descriptive statistics

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What are all members of a group that share a common characteristic of interest?

Population

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What is a subset of a population that shares the same characteristic of interest?

Sample

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We do research with samples because we don’t have access to what?

Entire populations

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What are used to make generalizations (inferences) from samples to populations?

Inferential Statistics

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Choosing a good sample affects what?

External validity

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What is the ability to generalize findings outside the sample?

External validity

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What type of sample adequately represents the population of interest?

Representative sample

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What type of sample does not adequately reflect the population?

Biased Sample

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What are the 2 major sampling strategies?

Probability

Non-probability

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Probability sampling uses what to choose a sample representative of the population to avoid bias?

Random selection

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Non-probability sampling doesn’t use random sampling so there is no guarantee of what?

that is represents a larger population

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What are the probability sampling methods?

True random sampling
Stratified random sampling
Systematic random sampling
Multi-stage random sampling

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In true random sampling every person in the population has?

An equal

Independent chance of being selected

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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

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What type of sampling randomly selects a starting place to choose participants?

Systematic random sampling

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What is used in systematic random sampling?

Systematic rule to select particiapnts

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In multi-stage random sampling the final random sample is selected through what?

Series of random selection decisions used to eliminate potential particiapnts

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What are the non-probability sampling methods?

Convenience 
Purposive
Quota
Systematic (non-random)
Stratified (non-random)
Multi-stage (non-random)

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In convenience sampling the sample is choosen based on what?

Convenient access

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In purposive sampling the sample is formed by including what?

Available persons who meet a specific criterion, but not randomly.

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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

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In systematic (non random) sampling the same is selected how?

Through a systematic, not random process

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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 ```