designing a scientific investigation

Investigative Skills

  • Hypothesis: concise statement predicting relationship between independent & dependent variables; no explanations.

  • Aim: “To determine/​investigate if … (independent variable) affects … (dependent variable).”

  • Variables

    • Independent: factor you manipulate (input).

    • Dependent: outcome you measure (response).

    • Controlled: all other factors fixed to ensure a fair test; specify how each is kept constant.

  • Method Requirements

    • Numbered or bulleted; logical, easy to follow; max ≈12 steps.

    • Use a range of at least 33 values for the independent variable.

    • State what is measured & how (instrument + unit).

    • Detail quantities, apparatus, and actions (SQAD: Statement–Quantity–Apparatus–Direction).

    • Repeat each trial ≥33 times; average to improve reliability.

    • Include a control (identical setup minus independent variable) to ensure validity.

    • All listed equipment must appear in the procedure.

Evaluation of Procedures

  • Good experiments are Fair, Accurate, Valid, Reliable.

  • Incomplete/inconclusive results often arise from

    • insufficient range of independent-variable values,

    • no replication.

  • Choose appropriate measuring devices (e.g. balance to 0.1 g0.1\,\text{g}).

  • Identify & mitigate

    • safety hazards (Bunsen burners, acids, corrosives),

    • errors (cross-contamination, mis-measurement).

Experimental Design & Presentation

  • Hypothesis: factual prediction containing both variables (e.g. “No bubbles will form above 37∘C37^{\circ}C”).

  • Aim: prove/​test the prediction (e.g. “Show enzymes denature above 37∘C37^{\circ}C”).

  • Controlled variables examples: pH, enzyme volume, light exposure.

  • Method Formatting

    • Provide brief apparatus list first.

    • Steps start with the equipment used; include units/directions.

    • Ensure sequence yields measurable results.

    • Include how to record, interpret, tabulate results; state repeats for consistency.

    • Must extend, not copy, any prior (Part A) method.

  • Marking cues

    • L: neat, numbered layout.

    • E: correct, explicit equipment use.

    • V: steps logically achieve aim; only independent variable changes.

    • R: specify recorded data, meaning, repeats, tabulation.

    • O: originality – method must be unique.