Consider the following hypothesis: Happy people live longer than unhappy people. How could one operationally define the variable so that it could be studied either using correlational or experimental methodologies? Your operational definition should be precise and clear enough that other researchers could replicate your study exactly. (I.e., Do not say, "Ask them." Tell us WHAT, specifically, you would ask and what the potential answer choices would 

I just think of this,
A journal of how happy and sad you are from this day.

Step-by-step explanation

Hi there,

You need a clinical diagnosis from psychologists to determine whether the person is in denial based on asked questions, or experiencing a hard time expressing thoughts. 
This study is hard to conduct and monitored on a daily and even years. 

One thing for sure, the process of collecting data can acquire through series of questions, and the basis will just always fall into how great participants can recall their past life. 

So my idea is similar from the previous study about nuns who wrote journals and have promising result.

link: science.howstuffworks.com

Why not conduct an experiment where participants write in a piece of paper/journal, "good words and happy thoughts" that triggers them to smile, laugh or giggle, comfortably happy and for the other part of participants, write bad things that could make their self sad and alone. 

One thing, If your day was good/bad, or even you experience a happy or sad things on this week. I think recalling moments can affect your actual mood and perception of happiness whenever you write something.

In that way, participants will record and recall "things that made them happy at that day" and on that moment there will be a chance of making them smile again and to express happiness once again while recalling their happy experiences. Even if its bad they tend to find happiness from it because they are only need to write good, nothing but a happy thoughts. On the other hand, "things that made them sad" they will tend to recall sad times and might trigger them to be sad again for that moment they are also need to write bad, nothing but a sad thoughts.

To be specific: 

Follow these format: 

For Happy Category Participants

I am happy and it made me smile because of these activity/thoughts/experience ____________*.

I wonder how happy am I if I will experience  ______________* again someday.

Happy to have/acquire this/these _________ * from this day/ week.

I am happy for this person: __________*

For Sad Category Participants

I am sad and it made me have a sad face because of these activity/thoughts/experience ____________****.

I wonder how sad am I if I will experience  ______________**** again someday.

I am sad that I do not have/acquire this/these _________*** from this day/week.

I feel sad for this person: __________***

*Happy thoughts only

***Sad thoughts only

Following these, If you are strict and just focused on saying thoughts that made you happy or sad. Continuously reminding participants for their chosen categories, as everyday you live in this world you are just expressing a happy or sad attitude towards your day.  How it will affect your lifespan in particular. 

Data will show how these simple writings will affect your emotions, perception, career, health, relationship to family and friends and also how long will you live in this world.

Final Note: If the variables cannot be attained by writing a everyday journal, maybe it could've been adjusted to a weekly basis.

and would a mixture of the feeling (Happy or Sad) does affect this experiment. Why not try to have 3rd group of participants where there will be a mixture of the said questions and ideas to made. Just another thing to share.

Hope you get my point
I am really wanted to push this ideas and help you out.

Thank you very much for sharing these.

Regards,
CGR