Before doing research in old records, it is a good idea to become familiar with all the variants in letter formation. Many errors are made by people who are not familiar with the handwriting styles of the colonial and pioneer periods in our country. Since I can't give you samples of old handwriting via email, I would like to recommend that you get a book on the subject and study it. You'll be glad you did. Both the capital and lower case versions of these two letters look the same in the handwriting of some of our ancestors.
Vowels are often hard to distinguish too.
When looking for a name, let's say, in the census, if you can't find it, try exchanging the vowell for every other vowel. Thus, the name Melissa may look like Melifsa and, therefore, be misinterpreted. Another possible pitfall in looking for our ancestors is not being familiar all the various nicknames that might have been used for a particular given name. One of my ancestors was named Mary Brandon. It wasn't until I learned that Polly was a nickname for Mary that I finally found her on the 1850 census in her father's household as Polly Brandon.