stats Flashcards
what does using midpoints assume
data normally distributed WITHIN classes
if air resistance improvement already used more improvements = ( on parachute)
parachutist does not fall vertically after chute opens; smooth changes in v; time for parachute to open; deceleration not constant
improvements to model ( air resistance not allowed)
rope being light; rope being inextensible; pulley being smooth; pulley being small; balls being particles
2 reasons stratified may be more suitable than simple random (2)
- observe relationships between subgroups
- rare or extreme cases represented proportionally
- stratified require larger sample size - lower variability within subgroups
2 reasons stratified sampling more suitable than quota sampling
- stratified is less biased
- cannot find sampling errors in quota
- stratified gives more accurate estimates as it’s a random process
explain what you understand by a random sample from a finite population (1)
(This is a sample where) every (possible) sample (of size n) has an equal chance of being chosen.
phrase to say at start of simple random sampling 3 marker
A ! list/register ! of all the students.
disadvantages quota
Not possible to estimate sampling errors
Process not random
what to say at end of quota
If a fish is caught and the species quota is full, then this is ignored.
what is stratified not suitable for
large populations
