Scientists can have confidence in their conclusions if the evidence gathered in the experiment is strong. Before confirming a link between variables, they will evaluate their experimental methods and measuring techniques, and review the data taken.
Here are some questions that you may need to consider when you evaluate your experiment.
Evaluation of method/experimental technique/improving accuracy.
Suggest improvements to method/measuring technique to improve confidence in the data and the conclusion.
Repeatability. How repeatable are your results? Did your results vary by large amounts? Did you have any off points on the graph, or anomalous readings in the table? How could you check these? Were enough repeat readings taken and a mean calculated? Is the sample size high enough?
Reproducibility. Did other groups following a similar method get the same graphs or patterns in their results, eg have you compared your graphs and data with other, different groups who followed the same method, to confirm the same conclusion has been reached? Was the range of the independent variable sufficient to show a pattern?