In order to understand this effect you need to know the story. I know that you had read it in your childhood day but I need you to read it one more time to understand it better.
Once upon a time, there was a beautiful girl named Cinderella. She lived with her wicked stepmother and two stepsisters. They treated Cinderella very badly. One day, they were invited for a grand ball in the king’s palace. But Cinderella’s stepmother would not let her go. Cinderella was made to sew new party gowns for her stepmother and stepsisters, and curl their hair. They then went to the ball, leaving Cinderella alone at home.
Cinderella felt very sad and began to cry. Suddenly, a fairy godmother appeared and said, “Don’t cry, Cinderella! I will send you to the ball!” But Cinderella was sad. She said, “I don’t have a gown to wear for the ball!” The fairy godmother waved her magic wand and changed Cinderella’s old clothes into a beautiful new gown! The fairy godmother then touched Cinderella’s feet with the magic wand. And lo! She had beautiful glass slippers! “How will I go to the grand ball?” asked Cinderella. The fairy godmother found six mice playing near a pumpkin, in the kitchen. She touched them with her magic wand and the mice became four shiny black horses and two coachmen and the pumpkin turned into a golden coach. Cinderella was overjoyed and set off for the ball in the coach drawn by the six black horses. Before leaving. The fairy godmother said, “Cinderella, this magic will only last until midnight! You must reach home by then!”
When Cinderella entered the palace, everybody was struck by her beauty. Nobody, not even Cinderella’s stepmother or stepsisters, knew who she really was in her pretty clothes and shoes. The handsome prince also saw her and fell in love with Cinderella. He went to her and asked, “Do you want to dance?” And Cinderella said, “Yes!” The prince danced with her all night and nobody recognized the beautiful dancer. Cinderella was so happy dancing with the prince that she almost forgot what the fairy godmother had said. At the last moment, Cinderella remembered her fairy godmother’s words and she rushed to go home. “Oh! I must go!” she cried and ran out of the palace. One of her glass slippers came off but Cinderella did not turn back for it. She reached home just as the clock struck twelve. Her coach turned back into a pumpkin, the horses into mice and her fine ball gown into rags. Her stepmother and stepsisters reached home shortly after that. They were talking about the beautiful lady who had been dancing with the prince.
The prince had fallen in love with Cinderella and wanted to find out who the beautiful girl was, but he did not even know her name. He found the glass slipper that had come off Cinderella’s foot as she ran home. The prince said, “I will find her. The lady whose foot fits this slipper will be the one I marry!” The next day, the prince and his servants took the glass slipper and went to all the houses in the kingdom. They wanted to find the lady whose feet would fit in the slipper. All the women in the kingdom tried the slipper but it would not fit any of them. Cinderella’s stepsisters also tried on the little glass slipper. They tried to squeeze their feet and push hard into the slipper, but the servant was afraid the slipper would break. Cinderella’s stepmother would not let her try the slipper on, but the prince saw her and said, “Let her also try on the slipper!” The slipper fit her perfectly. The prince recognized her from the ball. He married Cinderella and together they lived happily ever after.
So this was the story part. Now let’s talk some business.
In evolutionary psychology, the Cinderella effect is the alleged higher incidence of different forms of child-abuse and mistreatment by stepparents than by biological parents. Background
In the early 1970s, a theory arose on the connection between stepparents and child maltreatment. "In 1973, forensic psychiatrist P. D. Scott summarized information on a sample of "fatal battered-baby cases" perpetrated in anger (…) 15 of the 29 killers – 52% – were stepfathers.” Although initially there was no analysis of this raw data, empirical evidence has since been collected on what is now called the Cinderella effect through official records, reports, and census.
For over 30 years, data has been collected regarding the validity of the Cinderella effect, with a wealth of evidence indicating a direct relationship between step-relationships and abuse. This evidence of child abuse and homicide comes from a variety of sources including official reports of child abuse, clinical data, victim reports, and official homicide data. Studies have concluded that "stepchildren in Canada, Great Britain, and the United States indeed incur greatly elevated risk of child maltreatment of various sorts, especially lethal beatings". Studies have found that not biologically related parents are up to a hundred times more likely to kill a child than biological parents.
Powerful evidence in support of the Cinderella effect comes from the finding that when abusive parents have both step and genetic children, they generally spare their genetic children. In such families, stepchildren were exclusively targeted 9 out of 10 times in one study and in 19 of 22 in another. In addition to displaying higher rates of negative behaviors (e.g., abuse) toward stepchildren, stepparents display fewer positive behaviors toward stepchildren than do the genetic parents. For example, on average, stepparents invest less in education, play with stepchildren less, take stepchildren to the doctor less, etc. This discrimination against stepchildren is unusual compared with abuse statistics involving the overall population given "the following additional facts:
(1) when child abuse is detected, it is often found that all the children in the home have been victimized; and