data
are observations (such as measurements, genders, survey responses) that have been collected.
Statistics
is a collection of methods for planning studies and experiments, obtaining data, and then organizing, summarizing, presenting, analyzing, interpreting, and drawing conclusions based on the data.
Population
the complete collection of all elements (scores, people, measurements, and so on) to be studied. The collection is complete in the sense that it includes all subjects to be studied.
Census
the collection of data from "every" member of the population
Sample
A subcollection of members selected from a population
Parameter
a numerical measurement describing some characteristic of a population
Statistic
A numerical measurement describing some characteristic of a sample
Quantitative data
consist of numbers representing counts or measurements (158 lbs)
Qualitative Data
can be separated into different categories that are distinguished by some nonnumeric characteristic (male/female) [also called categorical or attribute data]
Discrete data
result when the number of possible values is either a finite number or a "countable" number. (i.e. the number of possible values is 0 or 1 or 2 and so on)
Continuous (numerical) data
result from infinitely many possible values that correspond to some continuous scale that covers a range of values without gaps, interruptions or jumps
Nominal level of measurement
characterized by data that consist of names, labels, or categories only. The data cannot be arranged in an ordering scheme (such as low to high) [e.g. colors, yes/no]
Ordinal level of measurement
can be arranged in some order, but differences between data values either cannot be determined or are meaningless (used for relative comparisons e.g. grades, ranks)
Interval level of measurement
like the ordinal level, with the additional property that the difference between any two data values is meaningful. However, data at this level do not have a natural zero starting point (where none of the quantity is present) [e.g. temperatures, years]
Ratio level of measurement
the interval level with the additional property that there is also a natural zero starting point (where zero indicates that none of the quantity is present). For values at this level, differences and ratios are both meaningful. [e.g. weights, prices]
Voluntary response sample
one in which the respondents themselves decide whether to be included [e.g. internet polls]
Observational study
we observe and measure specific characteristics, but we don't attempt to "modify" the subjects being studied.
Experiment
we apply some "treatment" then proceed to observe its effects on the subjects (subjects in experiments are called experimental units)
Cross-sectional study
Data are observed, measured, and collected at one point in time
Retrospective study
data are collected from the past by going back in time through examination of records, interviews, and so on. [also called case-control study]
Prospective study
data are collected in the future from groups sharing common factors called cohorts [also called longitudinal or cohort study]
Confounding
occurs in an experiment when you are not able to distinguish among the effects of different factors
Placebo effect
experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which is assumed to be an active agent
Blinding
a technique in which the subject doesn't know whether he or she is receiving a treatment or a placebo
Double-blind
an experiment in which neither the subjects nor the experimenter knows whether a subject is a member of the experimental group or the control group