Statistical investigations, simulation and probability decisions
School-entry workflows that construct displays, inspect fitted models, develop simulation evidence and justify probability-based decisions. Original synthetic practice is labeled; public artifacts and written reports require review and do not certify mastery.
Open any lesson. Completion records participation; automatic practice checks and human judgment of written arguments are separate. This unit retains its own versioned requirements.
Readiness and preparation
Check your starting point
Try these short questions on paper, then compare your reasoning. They are optional self-checks, not a placement score or a navigation requirement. Use a targeted review when useful and return with your browser’s Back control.
Why can two groups have the same mean but different shapes?
A single summary cannot replace a display of the observations.
Compare reasoning and find a refresher
The groups 0,5,10 and 4,5,6 both average 5 but have different spread. Inspect the values and their context before choosing a summary.
Comparing models requires a consistent sign and scale.
Compare reasoning and find a refresher
Residual means observed y minus predicted y for the same x. A positive residual is an observation above its prediction; a patterned residual plot can reveal a model mismatch.
How do random sampling and random assignment differ?
The two simulation workflows answer different questions.
Compare reasoning and find a refresher
Sampling selects who is observed from a population. Assignment chooses who receives which treatment among participants. Random assignment alone does not make participants representative of a population.