Exam Notes: Scientific Method & Data Analysis

Announcements and Reminders

  • Assignment 1 is due Friday at 11:59 PM.
  • Lab starts this week on Thursday or Friday, depending on your section.

Chapter 1: Scientific Method & Data Analysis

  • The Scientific Method:
    • Describes the procedures for developing and testing hypotheses.
    • Separates science from other disciplines.

Observation

  • Scientific studies begin with observations of natural phenomena.
  • Example: Toilets around the world look different.

Question

  • Observations give rise to questions that seek an explanation of the observed phenomenon.
  • Example Question: What’s the best way to poop? What is the most efficient and most comfortable pooping position?

Hypothesis

  • An answer to the question is proposed as a statement of cause and effect.
  • Example Hypothesis: If you poop in a specific position, then you will have the most efficient and comfortable bowel movement.
    • Independent Variable(s):
      • X-axis of results graph.
      • Predictor variable, potential “cause” of an effect.
      • Example: Specific position.
      • Other possibilities mentioned: Efficiency, comfort level, number of test subjects, type of food eaten.
    • Dependent Variable(s):
      • Y-axis of results graph.
      • Response variable, potential “effect” that we think depends on the independent variable.
      • Example: Efficiency, comfort level.
      • Other possibilities mentioned: Specific position, number of test subjects, type of food eaten.
  • Null Hypothesis:
    • States that there is no effect of the independent variable on the dependent variable.
    • Examples:
      • Pooping position has no effect on efficiency and comfort of bowel movement.
      • Pooping in a sitting position is the fastest and most comfortable position.
      • Pooping in a squatting position is the fastest and most comfortable position.

Prediction

  • Predictions that follow from the hypothesis must be identified and must be testable.
  • Example: If you poop in position X, then you will have the most efficient and comfortable bowel movement.

Hypothesis Testing

  • The predictions that follow from the hypothesis must be tested through observations and experiments (field and laboratory).
  • Data from these experiments must then be analyzed and interpreted to determine if they support or reject the hypothesis.

Study Example: Straining During Defecation in Three Positions

  • Study by Dov Sikirov, MD, published in Digestive Diseases and Sciences, Vol. 48, No. 7 (July 2003), pp. 1201-1205
  • Aim: Compare straining forces applied when sitting or squatting during defecation.
  • Methodology:
    • 28 healthy volunteers (ages 17-66 years) with normal bowel function.
    • Recorded time needed for sensation of satisfactory emptying in three positions:
      • Sitting on a standard-sized toilet seat (41-42 cm high).
      • Sitting on a lower toilet seat (31-32 cm high).
      • Squatting.
    • Recorded six consecutive bowel movements in each position.
    • Noted subjective impression of the intensity of the defecation effort.
  • Results:
    • Time needed for satisfactory bowel emptying and subjectively assessed straining were reduced sharply in the squatting position compared to both sitting positions (P < 0.0001).
  • Conclusion:
    • Sitting defecation posture necessitates excessive expulsive effort compared to squatting.

Characteristics of a Good Scientific Study

  • Healthy sample size (e.g., 28 volunteers).
  • Repeated samples (e.g., 6x per person).
  • Consistency across data collection.
    • Volunteers were supplied with a digital timer to record the time needed for sensation of satisfactory bowel emptying.
    • Used a predesigned form to record time.
    • Questionnaire for subjective assessment of any difficulties in defecation graded from very easy to very difficult.
  • No confounding variables.
    • Volunteers instructed not to change their usual diets and defecation habits.
  • Control group.

Data Representation (Graphs)

  • Independent variable goes on the X-axis.
  • Dependent variable goes on the Y-axis.
  • If the independent variable is categorical and the dependent variable is numerical, a bar graph is appropriate.
  • Example Results from Sikirov Study:
    • Time spent for bowel emptying according to position:
      • Squatting: Average time approximately 1 minute
      • Sitting, Height 31-32cm: Average time approximately 2 minutes
      • Sitting, Height 41-42cm: Average time approximately 3 minutes
    • Comfort level according to position (average assessment grade):
      • Squatting: Lowest difficulty score (best comfort)
      • Sitting, Height 31-32cm: Intermediate difficulty score
      • Sitting, Height 41-42cm: Highest difficulty score (least comfort)

Types of Experiments and Studies

  • Controlled Experiment:
    • Investigator manipulates independent variable and conditions of experiment.
    • Also called “Field Experiments” & “Laboratory Experiments”.
  • Comparative Experiment or Study:
    • Investigator studies naturally occurring variation in the independent variable.
    • Also called “Field Studies” or correlational study.

Using Models to Inform Predictions

  • Ecologists use mathematical & computer models.
  • Models: abstract, simplified representations of real systems.
    • Used to predict responses using a set of assumptions.
    • Predictions should be testable.