Chapter 11- sampling, Data Presentation and Interpretation (statistics) Flashcards
what is censuses sampling? what are its pros and cons?
census sampling is a survey of a whole population.
pros:
1) accurate representation
2) unbiased
cons
1)time, effort and money intensive
2) if members of a population are missed it could be biased
3) if the tested items are used up or damaged its impractical
what is a population?
the whole group of people is the population. its finite and countable
what is simple random sampling? what are is pros and cons?
simple random sampling is when every person has an equal chance of being chosen in the sample but each selection is independent of the others. often done using a random number generator
pros:
1) completely unbiased if everyone as an equal chance
cons:
1) can be inconvenient if the population is spread over a large area
what is systemic sampling? what are its pros and cons? how to dit?
systemic sampling is when every nth member of a population is selected. done by numbering the population from a full list. find a regualr interval. generate a random starting point as your first member of the sample. keep adding he interval to your sample.
pros:
1) can be used effectively in quality control
2 should be unbiased
cons:
1) if the number cosen lines up wit a pattern on the populus then it can be biased
what is stratified sampling? what are the pros and cons?how is it done? what’s the formula?
if a population is divided into categories, you can use stratified sampling where the same proportion of each category in the sample in the population is used. to do this divide a population into categories. use the formula to find how many needed for each category. randomly select the sample from each category.
(size of category in population / total population size) x total sample size
pros:
1) if there’s no overlap between them this is a representative sample
2) its useful when results vary depending on categories
cons:
1) can be expensive
what is quota sampling? what are the pros and cons? how is it done?
the interviewer is given a quota to fill and they fill it. to choose a quota sample divide a populous into categories. give each category a quota. collect data until quotas are met without using random sampling.
pros:
1) easy for interviewer
2) non response is less of a problem
cons:
1) can be biased. the interviewer may exclude some of the population
what is opportunity sampling? what are its pros and cons? how is it done?
opportunity sampling is when he sample is chosen from a section of the population that is most convenient for the sampler. chose members that are easiest to sample.
pros:
1) quick
2) cheap
3) easy
cons:
1) isn’t random
2) can be very biased
what is cluster sampling? pros and cons? how is it done?
cluster sampling is when the population is divided into distinct groups. the clusters should be groups you’d expect to give similar data.
to choose a custer sample:
divided the population into clusters covering the whole population, where no member belongs to multiple clusters. randomly select clusters. use either al the members or randomly sample.
pros:
1) practical( quicker and cheaper) for certain situations
2) adaptable as it can incorporate several sampling methods
cons:
1) less representative
2) not always possible to separate into clusters
what is self selection sampling? what are the pros and cons? how is it done?
self selection sampling is when people choose to be part of the sample.
how its done:
advertise or appeal to the whole population for participation. Then either use everyone who responds or take a sample of them.
pros:
1) quick and easy
2) non responders are less of a problem
3) it could be the only way to get people to respond
cons:
1) could be trends or strong opinions leading to bias
what are qualitative variables?
qualitative variables are non-numerical values
what are quantitative values?
quantitative values are values that are numerical
what’s the class width formula?
class width = upper class boundary - lower class boundary
what’s the class midpoint formula?
midpoint= (lower class boundary + upper class boundary) / 2
what’s the formula for frequency density?
frequency density = frequency / class width
what is a stem and leaf diagram?
stems leafs
1 137
2 45557
3 98
key:2 1 means 21
what’s the equation for standard variation?
