Statistics - Chapter 1 Sampling and Data
Observational Study
a study in which the independent variable is not manipulated by the study
Sample
a subset of the population
Lurking Variable
a variable that has an effect on a study even though it is neither an explanatory variable nor a response variable
Explanatory Variable
a variable that we think explains or causes changes in the response variable
Population
all individuals, objects, or measurements whose properties are being studied
Placebo
an inactive treatment that has no real effect on the explanatory variable
Simple Random Sampling
every member of the population has an equal probability of being selected for the sample, usually by using a random digit table or random number generator
Representative Sample
A subset of a population that closely matches the overall characteristics of the population
Quantitative Discrete Data
All data that are the result of counting
Qualitative Data
Data that is based on observable characteristics of things or events that can be collected using the five senses.
Control Group
a group in a randomized experiment that receives an inactive treatment but is otherwise managed exactly the same as other treatment groups
Cluster Sampling
a method for selecting a random sample and dividing the population into groups; use simple random sampling to select a set of groups. Every individual in the chosen groups is included in the sample.
Stratified Sampling
a method for selecting a random sample used to ensure that subgroups of the population are represented adequately; divide the population into groups (strata). Use simple random sampling to identify a proportionate number of individuals from each stratum.
Systematic Sampling
a method for selecting a random sample; list the members of the population. Use simple random sampling to select a starting point in the population. Choose every nth individual in the list starting with the one that was randomly selected.
Convenience Sampling
a nonrandom method of selecting a sample; this method selects individuals that are easily accessible and may result in biased data.
Proportion
a number of successes divided by the total number in the sample
Parameter
a number that is used to represent a characteristic of the population. It generally cannot be determined easily.
Statistic
a numerical measurement describing some characteristic of a sample
Experimental Unit
a person, object, or some other well-defined item upon which a treatment is applied
Treatments
different values or components of the explanatory variable applied in an experiment
Quantitative Continuous Data
has measurable values which can fall anywhere between a finite or infinite range
Sampling Bias
not all members of the population are equally likely to be selected
Blinding
not telling participants which treatment a subject is receiving
Double Blinding
the act of blinding both the subjects of an experiment and the researchers who work with the subjects
Sampling Error
the natural variation that results from selecting a sample to represent larger populations
Response Variable
the variable that is measured for change at the end of an experiment
Categorical Variable
variables that take on values that are names or labels