Statistics (sampling)

define population

define population

everyone in an investigation

define ‘sample’

representative of the population

define ‘census’

a survey of the entire population

define ‘Sampling frame’

a list of all members of the population

give an example of sampling frame

school register

define sampling unit

a distinct element of the population that can be picked to form a sample

list the 3 ways you can do random sampling

-hat method

- random number generator

-random number table

what is stratified sampling

the size of each group in the sample is in proportion to the sizes of the group in the population

what is the method for stratified sampling

split the population into groups and use the formula (stratified sample =strata divided by total X sample size) to calculate the sample size for each group and use random sampling to select members from each group

give 2 advantages of stratified sampling

sample is in proportion to population, so sample represents the population fairly

best used for populations with groups of unequal sizes

give a disadvantage of stratified sampling

time consuming

what is systematic sampling

choosing items in the population at regular intervals

what is cluster sampling

Population is divided into natural groups, groups are chosen randomly and every member of the group is sampled

give an example of when you’d use cluster sampling

when surveying lots of different towns in a country.

what is quota sampling

population is grouped by characteristics and a fixed amount is sampled from each group

what is oppurtunity sampling used for

using the people/items available at the time, e.g.": interviewing the first 10 ppl you see

what is judgement sampling

when the reasercher uses their own judgement to select a sample that they think represents a population.

what is the petersen capture recapture

used to estimate the size of large/moving populations where it’d be impossible to count the entire population

what is the equation for the petersen capture recapture

M/N = m/n —> first capture/total (N) = tagged/second capture

explain the method used for the petresen capture recapture

1- take a sample of the population

2- mark each item

3- put items back into the population and ensure theyre thouroughly mixed

4- take a second sample and count how many of your sample are marked

5- the proportion of marked items in your new sample should be the same as the proportion of marked items from the population in your first sample

what are Experiments

used when a researcher in how changes in one variable affect another.

what is a Explanatory (Independent) Variable

– The variable that is changed.

what is a Response (dependent) variable

The variable that is measured.

what is a Extraneous Variable

Variables you are not interested in but that could affect the result of

your experiment.

what are Laboratory Experiments –

Researcher has full control over variables. Conducted in a lab or similar

environment.

o Example of experiments - measuring reaction times of people of different ages.

list what the 3 types of variables would be

▪ Explanatory variable - age

▪ Response variable - reaction time.

▪ Extraneous variables - gender, health condition, fitness level etc.

what are Field Experiments

Carried out in the everyday environment. Researcher has some control over the variables. They set up the situation and controls the explanatory variable but has less control over extraneous variables.

o Example of field experiments – Testing new methods of revision.

list what the 3 types of variables would be

▪ Explanatory variable – method of revision

▪ Response variable – results in exam

▪ Extraneous variables – amount of revision pupils does, ability of pupils.

what are natural experiments

Carried out in the everyday environment. Researcher has no/very little control over the variables. Explanatory variables are not changed but instead researchers look at something that already exists in the world and how it affects other things.

o Example of natural sampling – the effect of education on level of income

list what the 3 types of variables would be

▪ Explanatory variable – level of education

▪ Response variable – income

▪ Extraneous variables – IQ, other skills people may have, personal circumstances

what is simulation

Simulation – A way to model random events using random numbers and previously collected data. These could be used to help you predict what could actually happen in real life.Easier and cheaper than actually collecting the data.

test protocol for simulation

1. Choose a suitable method for getting random numbers – dice, calculator, random number tables.

2. Assign numbers to the data.

3. Generate the random numbers.

4. Match the random numbers to your outcomes.