math

What is a discrete variable? A variable that is counted and takes distinct values.
What is a continuous variable? A variable that is measured and can take any value within a range.
How can you tell discrete from continuous? Counted = discrete; measured = continuous.
Reaction time rounded to the nearest 5 ms: which type? Continuous, because time is measured.
Number of bird calls: which type? Discrete, because calls are counted.
Volume of a bird call (dB): which type? Continuous, because volume is measured.
Number of defects per batch: which type? Discrete, because defects are counted.
Weight of defective items: which type? Continuous, because weight is measured.
What is stratified sampling? Divide the population into groups, then randomly sample from each group.
What is systematic sampling? Select people at fixed intervals, such as every 12th person.
What is convenience sampling? Choose people who are easiest to reach.
What is quota sampling? Select people until a set number from each group is reached, without requiring random selection.
What is the key difference between stratified and quota sampling? Stratified uses random selection; quota does not require random selection.
A researcher randomly selects students from each IB subject group. What method? Stratified sampling.
A theme park interviews every 12th visitor. What method? Systematic sampling.
A student surveys classmates they meet in the hallway. What method? Convenience sampling.
A company interviews 50 people in each age group until filled. What method? Quota sampling.
What is one disadvantage of convenience sampling? It may be biased and unrepresentative.
Why use stratified sampling? To ensure important population groups are represented.
What clue usually identifies systematic sampling? A fixed interval, such as every 5th or 12th person.