Population (151; also Ch. 13, 393)
group of individuals who have the same characteristics
 Target population (152) 
aka sampling frame: a group of individuals (or a group of organizations) with some common defining characteristic that the researcher can identify
Sample (152)
a subgroup of the target population that the researchers then select a sample for study
simple random samping (153)
the reseacher selects participants (or units, such as schools) for the sample so that any individual has an equal probability of being selectd from the populationmust have a Random Numbers Table
systematic sampling
you choose every nth individual or site in the population until you reach your desired sample size
stratifies sampling (154)
reseachers divide (stratify) the population on some specific characteristic (e.g. gender) and then using simple random sampling, sample from each subgroup (stratum) of the population (e.

g., females and males)

multistage cluster sampling (155)
the researcher chooses a sample in two or more stages because either the researchers cannot easily identify the population or the population is extremely large
nonprobability sampling (155)
the researcher selects individuals because they are available, convenient and represent some characteristics the investigator seeks to study
convenience sampling
resarcher selects participants bc they are willing and available to be studied
snowball sampling
the researcher asks participants to identify other to become members of the sample
sample error
the difference between the sample estimate and the true population score
instrument, (161)
a tool for measuring, observing or documenting quantitative data. Identified before the researchers collect datea, the instrument may be a test, questionnaire, tally sheet, log, observational checklist, inventory, or assessment instrument
choosing and modifying an instrument (167-169)
locating and existing instrument, obtaining permission to change it, and making changes in it to firt your requirmentsdeveloping steps: indentifying the purpose of the instrument, reviewing the literature, writing the questions, and testing the questions with individuals similar to those you plan to study (validating an instrument)
instrument reliability
score from the instrument are stable and consistent
validity (169, 172-74)
the individual’s socres from an instrument make sense, are meaningful and enable you, as the researcher to draw good conclusions from the sample you are studying to the population
nominal scales (categorical scales)
provide response options where participants check one or more categories that describe their traits, attributes or characteristicsgenderyes, no response list
semantic differential scale
bipolar adjectives that the participant uses to check his or her position (teenagers record their mood: alert vs. drowsy)
ordinal scales (ranking scales or categorical scales)
provide response options where participants rank from best or most important to worst or least important some trait, attribute or characteristic, information is categorical in a ranked order
interval scales (rating scales or continuous scales)
provide continuous response options to questions with assumed equal distances between options (ie Likert scale)
descriptive statistics (190)
indicate general tendencies in the data, spread the scores, or a comparison of how one score relates to all the others
measures of central tendancy
mean – averagemedian – middle of a set of scoresmode – the most frequently occurring score
measures of variability
range – the difference between the highest and lowest scores to items on an instrumentvariance – indicates the dispertion of scores around the meanstandard deviation – 66%