Chapter #4b - 09/25/24 Flashcards
how to get a good sample
define a “unit” :
is a single individual or object to be measured
define the “population” :
is the entire collection of units about which we would like information or the entire collection of measurements we would have if we could measure the whole population
what is another word for “the population” ?
universe
define “sample” :
the sample is the collection of units we actually measure or the collection of measurements we actually obtain
define “the sampling frame” :
is a list of units from which the sample is chosen. (ideally it includes the whole population ; ex. list of students enrolled at UWO, list of subscribers of a magazine, list of taxpayers)
define “sample survey” :
when measurements are taken on a subset, or sample, of units from the population
define “census” :
is a survey in which the entire population is measured
an opinion poll calls 5000 randomly chosen residential telephone numbers in lonfon and asks to speak with an adult member of the household. the interview asks “how many movies have you watched in a movie theater in the past 12 months?”. in all, 575 people responded. the sample in this survey is …
a) all adults living in london
b) the 5000 residental phone numbers called
c) the 575 people who respondents
c) the 575 people who respondents
what is a unit ?
An individual element or person from which data is collected in a study
what is a population ?
The entire group of individuals or items that you want to study or gather information about
what is a sample ?
smaller group selected from the population, used to represent the entire population in a study
what is a sample survey ?
A method of collecting data from a sample of the population to make inferences about the entire population
what is a sample frame ?
A list or database of all the units in the population from which the sample is drawn.
what is a census ?
A survey where data is collected from every unit in the entire population, rather than just a sample
define the “rate of nonresponse” :
is the percentage of people in a survey who don’t answer the questions
FILL IN THE BLANK
with proper sampling methods, based on a sample of 1500 adults, we can almost certainly estimate to within ___%, the percentage of the entire population who have a certain trait or opinion
3%
a polling firm sends an online questionnaire to 3000 employees at a tech company, asking, “do you work remotely more than 3 days a week?”. 450 employees complete the survey. the population in this surveu is :
a) all employees at the tech company
b) the 3000 employees invited to participate
c) the 450 employees who respondents
a) all employees at the tech company
what can a high nonresponse rate lead to ?
can lead to biased results because it may mean that certain groups are not represented
define “margin of error” :
is a measure of how much the results of a survey could differ from the true values in the population. It shows the range within which the actual value likely falls, usually expressed as a percentage
how do you calculate the margin of error ?
1 / √n
what does “n” represent ?
number
in early september 2003, california’s governor gray davis approved a controversial law allowing people who were not legal residents to obtain a California state driver’s license. that week the California field poll released a survey showing that 59% of registered voters opposed the law and 34% supported it. this part of the survey was based on a random sample of just over 300 people.
what is the approximate margin of error for the field poll results ?
a) 3.33%
b) 5.77%
c) 59%
d) 34%
b) 5.77%
how do you calculate the margin of error in the field poll study question ?
1 / √300 = 0.577 = 5.77%
when calculating the margin of error how many decimal places do u move and in what direction ?
two spots to the right
what is faster to collect? a smaple or a census ?
a sample is faster to collect than a census if the population is large
what is a census ?
when you collect data form every single person or item in a population, not just a sample
between a census and a sample, which includes everyone in order ot get a complete and accurate pictyre of the population ?
census
define “probability sampling plans” :
everyone in the population has a specific chance of making it into the sample
define “simple random sample”:
every conceivable group of people of the required size has the same chance of being the selected sample
what are the two things you need in simple random sampling ?
1) list of units in the population
2) source of random numbers (technology or table of random numbers)
is sampling the first 100 students of a list ordered alphabetically an example of a simple random sample?
NO
not an example of a simple random smaple
when calculating the margin of error is “n” represented by the population or the sample ?
sample
what are some sampling methods ?
- stratified random
sampling - cluster sampling
- systematic sampling
- random digit dialing
- multistage sampling
what is stratified random sampling ?
when you divide population in groups (strata) and take a simple random sample from each
what is the term used for when you divide a population into groups with similar traits (like age, gender, etc) and then randomly select samples from each group to ensure a fair representation ?
stratified sample
what is a “strata” ?
plural for “stratum”, meaning multiple subgroups within a population, each sharing a common characteristic
what is a stratum ?
subgroup or category within a population that shared a common characteristic (age, gender, etc.)
TRUE OR FALSE
in stratified sampling, the population is divided into these strata before selecting samples from each one
TRUE
what is cluster sampling ?
divide population into groups (clusters), take a random sample of clusters and measure all the units of selected clusters
what is systematic sampling ?
divide population into as many consecutive segments as you need, randomly choose a starting point in the first segment, then sample at that same point in each segment
what is an advantage to cluster sampling ?
need only a list of clusters, not a list of all individual units
