Population Sampling

Population Sampling

Population Sampling

• 'Population' means the entire category

• 'Sample' means a portion of the population

Types of Statistics

• A census is the process of collecting data from every member of the population

• Population statistics use data collected by a census

• Sample statistics only use data from a sample

• Polls are used to collect data that can be used to calculate sample statistics

Uses of Sampling

^{The proportion of different categories in sample can be used to estimate the number of each category in a population.}

A sample of 300 fish is taken from a lake, tagged and released. Some time later, a second sample of 80 fish is taken and 8 of these have tags. What is the estimated fish population for the lake?

Fill in the Blank

A large black box is filled with 300 balls that are all of the same size. The balls are red, yellow and blue. A sample of 20 balls is taken and 9 are yellow, 7 are red and the rest are blue. What is the estimated total number of blue balls in the box?

Sampling bias

• The word bias means a distortion or problem with information, or a preference or belief that is not supported by evidence

• A sampling bias occurs when the sample was selected in a distorted or unfair way and therefore does not truly reflect the population

Multiple Choice

Which of the following methods will NOT result in a biased sample?

• You want to know the favourite sport of a city so you ask people at an AFL football match

• Every third student arriving at school through the front gate in the morning are asked if they like reading

• Randomly select people from the local phonebook and conduct a phone poll in order to do a survey on the use of parks in your suburb

Inappropriate methods of sampling

• Judgemental sampling occurs when a sample of people is selected because of their special knowledge.

• Convenience sampling is asking people who are easy to find.

• Both sampling methods are likely to be unreliable and biased

Multiple Select

Which of the following is an example of convenience sampling

• All of the members of a quilting group are asked what brand of sewing machine they prefer

• Asking Pokemon Go players which Pokemon is best

• Going on Tik Tok and commenting on other people to ask if they like the App

• Ask people who sits with you during lunch break whether they prefer cats or dogs.

Random Sampling

• The best way to collect unbiased data is to use random sampling

• This is where each member of the population has an equally likely chance of being chosen in the sample.

Multiple Choice

Which of the following is an example of random sampling?

• Measuring the height of students from one class of 7F1 to find the average height of the whole school

• Asking people as they enter the supermarket which is their favourite supermarket

• Assigning numbers to everyone and picking out random numbers to survey

• You want to find out he health issues in your community, so you question people who come into the local medical clinic

Bias in experiments

• Coins and dice are often used to collect data and calculate sample statistics

• Unbiased or fair coins and dice must be used

• This can be proven by running a large number of trials

Multiple Choice

A die is rolled 60 time and the result for each outcome is recorded. This experiment is repeated so that five sets of results are collected (as shown). Which die do you think is fair?

• Set 1

• Set 2

• Set 3

• Set 4

• Set 5

Practice Time!

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