Presentation on theme: "Writing Good Experimental Methods Grade 10 - ISP."— Presentation transcript:
Writing Good Experimental Methods Grade 10 - ISP
And ethics get involved… Milgram expt.
Review of terms Independent Variable Dependent Variable Controlled Variables Confounding Variables Control Group
Internal Validity Internal validity is a measure which ensures that a researcher’s experiment design closely follows the principle of cause and effect.Internal validity cause and effect
How to ensure you have Internal Validity? Are your variables controlled? Can you say that A causes B because you know that no other confounding variable has arisen? Are your measuring devices or tools actual measures of what you want? (e.g. survey questions actually get at behaviour you want)
External Validity The main criteria of external validity is the process of generalization, and whether results obtained from a small sample group, often in laboratory surroundings, can be extended to make predictions about the entire population.generalization results
How to ensure you have External Validity Representative sample size Adequate # of samples, specimens, or subjects in each experimental category Repeated, multiple trials Representative sample
Reliability The idea behind reliability is that any significant results must be more than a one-off finding and be inherently repeatable. (Experiment can be replicated by you and others)reliabilitysignificant resultsrepeatable Other researchers must be able to perform exactly the same experiment, under the same conditions and generate the same results. This will reinforce the findings and ensure that the wider scientific community will accept the hypothesis.experiment hypothesis
How to ensure you have reliability Specific method with all of the equipment and steps described in detail Measuring devices are calibrated correctly All variables are controlled in every trial. Repeat trials to see if consistent
Method Writing Characteristics of a good method –Specific language and descriptions –Number your steps –Written in past passive (avoid I) –Use “repeat steps # x to x” –Mention any controlled variables and how you dealt with them
A good method Using the sticky labels and the marker pen label the bags. Mark 5 bags as ‘A’, 5 as ‘B’ and 5 as ‘C’. You also need to label each set of bags 1 to 5. Cut the bread into 10 x 10 squares using the chopping board and knife. Inoculate the bread thoroughly with the mold solution. Try to coat each slice with a similar amount of the culture although this can be difficult. Put one slice of this bread into each bag and seal the bags tightly. Put the 5 ‘A’ bags into the freezer, the 5 ‘B’ bags into the refrigerator and the 5 ‘C’ bags somewhere safe in a warm room. Because the bags in the freezer and fridge will not be getting much light it is best to cover the ‘C’ bags to make sure that light is a constant. Every 24 hours, preferably at exactly the same time every day, using the plastic grid, count the number of square centimeters of mold on each slice of bread. If the mold covers more than half a square, count it as 1cm, if less than half a square, count as 0 cm. You must never open the bags. You should repeat these counting processes for 10 days or until there are significant measurable results.significant measurable results Keep a careful note of your results for each slice of bread for the entire duration of the experiment. You can even take pictures or draw the slices if you want to be really scientific! Average the results for sample types A, B and C. Once you have finished, throw out all of the bags without opening them.
Types of graphs Bar graphs compare different discrete factors (separate values only) Line graphs show continuous variables (all values are allowed)