Sampling Techniques, Types of Variables, Levels of Measurement

Sampling

a sample should have the same characteristics as the population it is representing

Sampling can be:

with replacement: a member of the population may be chosen more than once (picking the candy from the bowl)

without replacement: a member of the population may be chosen only once (lottery ticket)

Sampling methods can be:

random (each member of the population has an equal chance of

being selected)

nonrandom

The actual process of sampling causes ___. For example, the sample may not be large enough or representative of the population.

sampling errors

Factors not related to the sampling process cause ___.

nonsampling errors

A defective counting device can cause a ___.

nonsampling error

Random sampling methods

simple random sample

stratified sample

cluster sample

systematic sample

each sample of the same size has an equal chance of being selected

simple random sample

divide the population into groups called strata and then take a sample from each stratum

stratified sample

divide the population into strata and then randomly select some of the strata. All the members from these strata are in the cluster sample.

cluster sample

randomly select a starting point and take every n-th piece of data from a listing of the population

systematic sample

The collection of data that are relevant to the problem being studied is commonly the most difficult, expensive, and time-consuming part of the entire research project.

statistical data

___ are usually obtained by counting or measuring items.

Statistical data

Primary data are collected specifically for the analysis desired

Secondary data have already been compiled and are available for statistical analysis

___ is an item of interest that can take on many different numerical values.

variable

A ___ has a fixed numerical value.

constant

Statistical data are usually obtained by counting or measuring items. Most data can be put into the following categories:

Qualitative - data are measurements that each fail into one of several categories. (hair color, ethnic groups and other attributes of the population)

Quantitative- data are observations that are measured on a numerical scale (distance traveled to college, number of children in a family, etc.)

___ are generally described by words or letters. They are not as widely used as quantitative data because many numerical techniques do not apply to the qualitative data.

qualitative data

Qualitative data can be separated into two subgroups:

dichotomic (if it takes the form of a word with two options (sex - male or female)

polynomic (if it takes the form of a word with more than two options (education - primary school, secondary school and university).

___ are always numbers and are the result of counting or measuring attributes of a population.

quantitative data

Quantitative data can be separated into two subgroups:

discrete (if it is the result of counting (the number of students of a given ethnic group in a class, the number of books on a shelf, ...)

continuous (if it is the result of measuring (distance traveled, weight of luggage, …)

Numerical scale of measurement:

nominal

ordinal

interval

ratio

___ consist of categories in each of which the number of respective observations is recorded. The categories are in no logical order and have no particular relationship. The categories are said to be ___ since an individual, object, or measurement can be included in only one of them.

nominal, mutually exclusive

___ contain more information. Consists of distinct categories in which order is implied. Values in one category are larger or smaller than values in other categories (e.g. rating-excelent, good, fair, poor)

ordinal

___ is a set of numerical measurements in which the distance between numbers is of a known, sonstant size.

interval

___ consists of numerical measurements where the distance between numbers is of a known, constant size, in addition, there is a nonarbitrary zero point.

ratio