
Experiment
A treatment is applied to part of a population and responses are observed. Another part of the population may be used as a control group, in which no treatment is applied. In many cases, subjects in the control group are given a placebo, which is a harmless, unmedicated treatment, that is made to look like the real treatment. The responses of the treatment group and control group can then be compared and studied. For instance, an experiment was performed in which diabetics took cinnamon extract daily while a control group took none. After 40 days, the diabetics who took the cinnamon reduced their risk of heart disease while the control group experienced no change.

Observational Study
A researcher observes and measures characteristics of interest of part of a population but does not change existing conditions. For instance, an observational study was performed in which researchers observed and recorded the mouthing behavior on nonfood objects of children up to three years old.

Ration level of measurement
Data at this level are similar to data at the interval level, with the added property that a zero entry is an inherent zero. A ratio of two data values can be formed so that one data value can be meaningfully expressed as a multiple of another.

Interval level of measurement
Data at this level can be ordered, and you can calculate meaningful differences between data entries. At the interval level, a zero entry simply represents a position on a scale, the entry is not an inherent zero.

Ordinal level of measurement
Data at this level is qualitative or quantitative. Data at this level can be arranged in order, or ranked, but differences between data entries are not meaningful.

Nominal level of measurement
Data at this level is qualitative only. Data at this level are categorized using names, labels, or qualities. No mathematical computations can be made at this level.

Quantitative Data
Consist of numerical measurements or counts.

Qualitative Data
Consist of attributes, labels, or nonnumerical entries.

Inferential Statistics
Is the branch of statistics that involves using a sample to draw a conclusions about a population. A basic tool in the study of inferential statistics is probability.

Descriptive Statistics
Is the branch of statistics that involves the organization, summarization, and display of data.

Statistic
Is a numerical description of a sample characteristic.

Parameter
is a numerical description of a population characteristic.

Sample
Is a subset of a population.

Population
Is the collection of all outcomes, responses, measurements, or counts that are of interest.

Statistics
Is the science of collecting, organizing, analyzing, and interpreting data in order to make decisions.

Data
Consists of information coming from observations, counts, measurements, or responses.

