How do researches avoid presentism?

What are the causes of this disease and how is it transmitted sickle cell anemia? What is an AED certification? Where you can have shingles? What type of variation is eye colour? How will Boeing's Flying Wing plane not cause claustrophobia? Why do you have both really dry ear wax that sticks to you ear like a scab but isn't and also wet wax at the same time that i can't get rid of becaouse i constantly have buildup of wax? What is glandular fever? What is functionally deaf? Which highly infectious disease were decleared in1979 to having completely eradicated in India? Can shingles or chickenpox be transferred by a third party? Which receives urine from the renal papilla the minor calyx or the minor calyx? What causes a sudden fainting in the shower? Where can you get paneer booti in Canada? What are some of the symptoms of a brain tumor? What is the human anatomy involved in Spina Bifida? What muscles extends and abducts the wrist? Did pilgrims on the mayflower experience cruel treatment poor sanitation conditions starvation disease and overcrowding and imprisonment? What happen if the patients having pulmonia is didn't get well.? What does the triceps do when you bend the elbow? Why would groin lymph nodes still be swollen after abscess if blood work is normal?

How do researches avoid presentism?