Question

Which experimental design decision would most likely produce invalid and unreliable results

Answer 1

There are plenty decisions that can invalid a experimental research:

1. Wrong design to wrong experiment.
2. Don't isolate variables of study.
3. Consider the wrong variables or wrong indicator of them.
4. To apply subjective analysis.

These are basic decisions that, normally, are taken.

Answer 2

Having more then one independent variable will give unreliable results. Hope this helps