Individual, Group & Mass Extension Teaching Methods, Audio-Visual Aids (Edgar Dale's Cone of Experience) - Agricultural Extension Education | Agrigyan

• Controlling Extraneous Variables in Experimental Research:
• In experimental design, extraneous confounding variables that threaten internal validity can be controlled through:

• Eliminating the variable as a variable: Holding the variable constant across all conditions (e.g., selecting only one gender or one soil type).
• Matching subjects: Pairing subjects with identical extraneous characteristics across experimental and control groups.
• Randomization: The most powerful tool for distributing unknown variables equally.
  • Conclusion: Both (1) and (2) are established experimental control approaches, making Option 4 correct.

• Systematic Sampling:
• Systematic Sampling is a probability sampling method where sample units are selected from a comprehensive ordered sampling frame at regular fixed intervals:

• random starting point between $1$ and $k$ is chosen, and every $k$-th case thereafter is systematically drawn until the desired sample size $n$ is reached.
• Distractors: Stratified sampling divides the population into strata; quota sampling is non-random; convenience sampling selects easily accessible units.

Correct option: (2) Systematic sampling