stad 2300

Entities measured and studied

Individuals

The entire group to be studied

Population

Subset of pop. from which you collect data

Sample

Numerical summary of population

Parameter

Numerical summary of sample

Statistic

Methods for summarizing collected data via tables, graphs, numerical summaries (averages or percentages)

Descriptive statistics

Methods that take a result from a sample, extend it to the population and measure the reliability of the result. Always contains uncertainty

Inferential stats

Any characteristic of the individuals within the pop.

Variable

What values a variable takes and how often it takes those values

Distribution of variable

If observation takes on numerical values

Quantitative

If each observation belongs to a set of categories

Qualitative variable

Measurement if the values of the variable name, label, or category. Doesn’t allow for ranking

Nominal (qualitative)

Measurement if the variable has properties of nominal level but can be ranked

Ordinal (qualitative)

Measurement if the variable has the properties of the ordinal level but each difference in value has meaning. (A value of zero doesn’t mean the absence of the quantity)

Interval level (quantitative)

Measurement if the variable has the properties of the interval level but the ratios of the value has meaning. A value of zero means absence of quantity

Ratio level (quantitative)

When someone assigns individuals in a study to certain experimental conditions then observed outcomes

An experiment

When someone observes and records the behavior of the individual without imposing any conditions

Observational study

Explanatory variable that was not considered in the study but that affects the value of the response

Lurking variable

characteristics typical of those possessed by the population of interest

Representative sample

n subjects from a population of N size in which each possible sample size of n has the same chance of being selected (n = sample, N = pop.)

Simple random sample

When dividing the population into separate groups called strata then selects a simple random sample from each stratum. (Each stratum should be homogeneous in some way w respect to variable of interest)

Stratified sample

Dividing the population into large number of clusters then a simple random sample of clusters is selected and all individuals in the selected clusters are included

Cluster sample

Selecting every kth individual from a pop. first individual selected corresponds to a random number btween 1 and k

Systemic sample

When the technique used tends to favor one part of the pop. over another

Sampling bias

When individuals selected to be in the sample who do not respond have different opinions from those who do respond

Non response bias

Response bias

When the answers on a survey do not reflect the true opinions of the respondents

Subject do not know what treatment they’re receiving

Single blind experimen

Neither subject nor researcher knows what treatment they’re subject is getting

Double blind experiment

frequency distribution

listing each category of data and the number of observations in each

listing category of data together with the relative frequency and the proportion of observation in each category. found by taking the frequency for a particular category and dividing by total number of observations

relative frequency distribution