Chapter 11- Populations And Samples Flashcards
What is the goal of sampling in quant research
Make generalizations abt the pop from which the sample was drawn
Def population
A complete set of persons or objects that possess some common characteristic of interest to the researcher
What 2 groups is the population composed of
Target pop
Accessible pop
Def target pop
The entire group or objects to which the researcher wishes to generalize the findings of a study
T/f- the target pop meet the designated criteria of interest
True
When is an accessible pop used
When the researcher cannot obtain a list and obtains a sample from an available group
Def element
A single member of a pop
Def sampling frame
A listing of all elements of a pop
Name the 2 types of sampling methods
Probability
Non probability
Name the types of probability sampling (4)
Simple random sampling
Stratifies random sampling
Cluster random sampling
Systematic random sampling
Def probability sampling
The use of a random selection process to obtain a sample from members or elements of a population
What is the goal of probability sampling
Obtain representative elements of pop
Probability sampling FYI
- each pop element has a known chance or probability of being selected for the sample
- investigators bias does not interfere
Def simple random sampling
Ensures each element of the pop has an equal chance of being chosen
Simple random sampling includes _____. ______ _______
Table of numbers
Def table of random
- a group of numbers in nor order or sequence
- each number has an equal chance of being selected
Def stratified random sampling
Population is divided into 2 subgroups or strata according to some variable of importance.
- simple random sample is taken from each subgroup
Def proportional stratified sampling
Obtaining a sample from each stratum that is proportional to the size of the stratum in the total pop
Def disproportional stratified sampling
Selection of members from strata in which the number of members chosen from each stratum is not in proportion to the size of the stratum in the total pop
What should be considered when using disproportional stratified sampling
Weighting- an adjustment process
Def weighting
- an adjustment process that involves simple computations
- adjustments allow a better estimate if the actual pop values
When is cluster random sampling used
Large scale studies
Def cluster sampling
Large groups , or clusters become the sampling units
What is the draw back of using cluster random sampling and how can it be compensated
- sampling error incr with each stage of sampling
- compensate by using larger samples
Def systemic random sampling
Selects every kth element of pop
Steps of systematic random sampling
- obtain a list of total pop (N)
- determine size of sample (n)
- determine sample interval width = N/n
Def non probability sampling
Sample elements are chosen from the pop by no random methods
What is the draw back to using non probability sampling
More likely to produce a biased sample
Why would non probability sampling be used
Convenience
List the different methods of non probability sampling
Convenience
Quota
Purposive
Def convenience sampling
- aka accidental/ incidental
- choosing readily available ppl or objects for a study
Benefits of using convenience sampling
Saving time and money
Def snowball sampling/ network sampling
The assistance of study subjects to help obtain other potential subjects
Def quota sampling
- first step involves dividing the homogenous strata and selecting same elements from each of these strata
- obtain members through convenience samples
Def purposive sampling
Hand picking of subjects
Aka judge mental sampling
Subjects are chosen that the researcher believes represent the pop
- based on the assumption that the researcher/ chosen expert has enough knowledge abt the pop of interest to select specific subjects for the study
Which most often uses purposive sampling- quant or qual studies?
Qual
Def longitudinal study
Follows subjects over a period of time in the future
Def cross sectional study
Examines subjects at one point in time
Def cohort study
Focus is on a subgroup of a pop , frequently persons who are of a simian age group
T/f - quant studies use much smaller sample sizes than qual studies
False- qual use smaller sizes
When may large sample sizes be needed
- many uncontrolled variables
- small differences expected in members
- pop must be divided into subgroups
- drop out rate expected to be high
- statistical tests require minimum sample sizes
Def power analysis
A,procedure that can be used to determine the needed sample size
Def sampling error
The difference bx data obtained from a random sample and the data that would be obtained if an entire pop were measured
T/f- sampling error is controlled by the researcher
False- not under the researchers control
What is sampling error caused by
When a sample is chosen to represent a pop
Def sampling bias
Sampling errors and bias are caused by the researcher if samples are not carefully selected
Def volunteers
Subjects who approach the researcher asking to participate in the study
How is volunteer sample diffent from a convenience sample
Convenience sample participants are approached by the researcher
Draw backs of volunteer sample elements
- volunteers may take greater risks than non volunteers
- may be motivated by monetary or other types of rewards
Def random sampling
The selection of a sample from them pop
Def random assignment
The unbiased placement of the subjects to either the experimental or control groups Ina. Study
Which type of sampling is necessary for a true experimental design
Random assignment
